Kim Skinner's Posts (79)

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Plaster Finishes Should Last 20 Years

All pool plaster finishes should last 20 years or more. However, some last only 5 to 7 years, and some less than a year before the plaster surface deteriorates, discolors, and looks terrible.

Why the difference? Very often, plaster quality. As we have pointed out previously, studies on pool plaster and cement/concrete flatwork have shown that poor workmanship practices have the greatest effect on durability, deterioration and discolorations. Various studies also confirm that water chemistry plays only a minor role.

Fortunately, there are a lot of quality plasterers that understand the importance of proper plastering, and generally take an extra hour or two to properly plaster pools with good materials and good workmanship practices. Their pools usually last 20+ years.

However, there are some poor-quality plasterers that are in a hurry and use inferior and “short-cut” practices and/or materials to plaster quickly. Doing so allows them to underbid the quality plastering companies. Their pools usually last less than 5 years, and sometimes less than a year before the plaster problems begin. And when the plaster finish starts looking bad, they simply blame the water chemistry instead of their own sloppy workmanship. Sadly, they are enabled to do that by the NPC and APSP.

A “Pretend” Plastering Standard

A few years ago, the NPC and APSP got together to write an ANSI plaster standard. Unfortunately, they refused to mention and include important and critical workmanship requirements (well known by the cement and concrete industry) that would produce quality, durable, and discoloration-free plaster/cement finishes. No limits or standards at all!

Furthermore, the APSP/NPC standard doesn’t mention the defects, deteriorations, or discolorations that can result due to improper and inferior workmanship. That means there is no accountability for plasterers that do poor work. Sounds like a “protection” standard. Pool builders and State Contractor License Boards have little recourse to help pool owners.

What about Water Chemistry Standards?

On the other hand, APSP and NPC have very strict and narrow standards for pool water maintenance. Beyond that, their literature (incorrectly) suggests that if pool water is not maintained within their suggested water parameters, that plaster problems will result. No, in reality plaster studies show that slightly aggressive LSI water does not cause the defects or discolorations at issue.

The NPC and APSP should not be exaggerating and misusing the importance of proper water balance which leads to service techs and pool owners being incorrectly blamed for many different plaster problems.

Obviously, poor water chemical maintenance can result in uniform etching and/or scaling. Even some types of metal staining can be traced to chemical mismanagement. However, when plasterers attempt to associate spotting, streaking, mottling, discoloration of the paste, calcium nodules, spalling, etc. to water chemistry causes, you know there is no basis for that. They are factually known to be caused by improper materials, application or curing failures.

The Bottom Line

APSP and NPC should rewrite the ANSI Plaster standard and adopt applicable workmanship standards (similar to ACI and PCA standards) to promote durable and discoloration-free plaster finishes for pool owners. That would serve the industry much better and help prevent plaster problems occurring in the first place.

However, this ongoing travesty probably won’t change until the entire pool industry becomes informed of these issues, rejects the false claims that water balance is what causes the above plaster problems, and demands that the NPC and APSP make things right.


When a plaster finish develops discoloration or defects, the following questions should be asked.

What does adding too much water, or too much calcium chloride (hardening accelerator), or performing too much water troweling, or overly late and excessive hard troweling do to plaster finishes? 

And wouldn’t “tenting” pools (to overcome harsh weather conditions) and taking an extra hour help to produce a higher-quality plaster finish?

Those are the important issues that are missing from the APSP/NPC/ANSI Plaster Standard.

The following links provide additional details regarding these issues.


Comments and questions are welcomed.

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Is Pool Water Balance Always the Problem?

For 50 years, the pool industry has considered pool water within an LSI of -0.3 and +0.5 to be acceptable and balanced. But recently, and without providing any supporting science or research, the NPC is trying to convince the industry that any negative LSI (-0.1 to -0.3) is unacceptable and immediately detrimental to pool plaster. Their theory also suggests that an alkalinity below 80 ppm, or a low calcium level (below 200 ppm) independently as being automatically aggressive even if the LSI is positive.

It is also being claimed that those water conditions cause gray mottling (of white plaster), craze cracking, variable white blotchiness and streaking of colored plaster, random calcium nodules, and plaster flaking (spalling) to occur in just a few weeks or months. That is all nonsense.

Contradictions to Those Claims

Let’s consider that plaster consultants recommend adding 8 to 10 gallons of acid to a 20,000-gallon pool for one week to improve the aesthetic appearance of new plaster finishes, including quartz and pebble. That acid treatment (or acid start-ups, now disingenuously referred to as “hot start-ups” by plasterers) lowers the pH to about 3.5, the alkalinity to a negative number (below zero), and the LSI to -4.0. That water is about 5,000 times more aggressive than an LSI of -0.3. If that type of water doesn’t cause the above plaster issues, how then could water that is 5,000 times less aggressive do that?

Plaster experiments show that those acid treatments dissolve and etch up to 30 pounds of calcium material from the plaster surface and, assuming the surface is relatively of consistent quality, do so uniformly without causing discoloration. (btw, the total weight of plaster material in a 20,000-gallon pool is about 4000 pounds).

In comparison, maintaining an LSI of -0.3 for six months may dissolve about 1.5 pounds of calcium material. In other words, it takes at least 10 years of consistently maintaining an LSI of -0.3 to equal the same uniform etching effect of adding 10 gallons of acid for one week. Note: It is very difficult to constantly maintain a negative LSI because aggressive water seeks to balance itself as it liberates calcium from the plaster surface, and the pH generally rises.

More Contradictions

The NPC/Cal Poly (NPIRC) plaster study was used to mislead the industry regarding aggressive water chemistry. Reviews by two Ph.D. chemists indicated that the (fabricated) conclusions don’t match the results and data. Those studies actually demonstrated that deterioration and spotted discoloration occurred in balanced (non-aggressive) water and in only four months. That implicates poor workmanship or materials as the problem, not aggressive water.

The Portland Cement Association and the American Concrete Institute do not blame rain (aggressive water) for causing rapid discolorations and defects on cement/concrete surfaces. Instead, they have identified improper workmanship and material issues as causes. Rain is about 1,000 times more aggressive than an LSI of -0.3 (which occurs often in pools), and yet, does not cause similar defects or discolorations (as mentioned above) on cement sidewalks and driveways, even after several years.

For many years, thousands of pools across the country have been intentionally (and unintentionally) maintained with slightly aggressive water to prevent calcium scaling, and they do not develop plaster discolorations or defects.

There are petrographic (forensic) plaster studies showing that improper and “short-cut” practices cause plaster discoloration and deterioration problems, some of which only become visible after pools are filled, and sometimes even after months. See this link:

The Bottom Line

Maintaining slightly aggressive water (LSI -0.1 to -0.3) is acceptable. It does not cause rapid plaster deterioration and discolorations problems on quality applied pool plaster. The plaster problems mentioned above are prevented by following good workmanship standards. Right now, there are none. Good standards would provide accountability, slow down the plastering process, and give pool owners a quality and beautiful plaster finish that lasts 20 years.


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Are All Color Pigments Good for Pool Plaster

There are two important issues involved when trying to achieve quality colored pool plaster that will remain durable, attractive, and the proper shade for many years.

The first issue is to utilize superior workmanship practices to achieve good color, with minimal mottling, and no blotchiness, white streaking or soft spotting, which our previous email update addressed. (Note: Some pool owners prefer the slight mottling variation that is normal for colored plaster).

The second issue is using quality color pigments (added to plaster mixes) that will hold up well for years and not lose its’ color in a swimming pool environment, which is the topic of this update. One would think that all color pigments used in pools are colorfast, meaning that the color doesn’t fade or become bleached in chlorinated water or in sunlight.  Sadly, that is not the case.

What has been learned?

The onBalance team has conducted many experiments with various pool plaster products, such as pebble and quartz exposed aggregate products that contain color pigments.

It appears the plaster products that contain “organic” pigments become bleached (loss of color) over time when subjected to chlorine (an oxidizer). But products with “inorganic” pigments generally do not become bleached. Additionally, experiments which subjected both organic and inorganic pigments to LSI aggressive water showed that neither type of pigment lost their color from etching.

When an organic pigment, phthalo blue for example, is bleached and loses its color over time in chlorinated water, the plaster surface becomes “whitish” because it is made with white Portland cement.

However, it was also observed that when two (or more) color pigments are added to a plaster product mix to obtain a unique and special color, and the blue organic pigment became bleached and faded, the other color pigment(s), if inorganic and colorfast (often a gray or brown pigment), remains unaffected, intact, and becomes the dominate color.

Obviously, only pigments that are colorfast are appropriate for swimming pool finishes.

Question: Why would material manufacturers and plasterers sell and use non-colorfast pigments that will not keep their color? One reason may be that organic (non-colorfast) pigments are usually much cheaper than the superior (colorfast) inorganic pigments. Of course, that allows some companies to underbid the quality-oriented companies.

Who Takes Responsibility or Not

The NPC has a Technical Bulletin addressing common color pigment problems. Amazingly, their bulletin does not mention anything regarding colorfastness and that (organic) color pigments can be bleached by chlorine or other oxidizers. Plus, no acknowledgement that excessive water troweling can cause white streaking, soft spotting, or blotchiness to slowly develop over time. And no mention that calcium chloride (hardening accelerator additive) should not be used with colored pigments as manufacturers WARN against, as it also contributes to severe blotchiness.

Instead, the NPC suggests that “aggressive water” causes color fading or whitening of colored plaster (along with causing many other plaster defects and discolorations), all of which is false. Of course, calcium scaling can mask the color, but that can be easily determined and rectified.

The plaster industry has misled the industry that water chemistry has the most significant and negative effect on the durability and color of plaster. To the contrary, there are various plaster/cement studies that have shown that poor workmanship and materials have a greater effect.

Think about this: Plasterers and material manufacturers generally recommend performing extremely aggressive “acid bath” or “hot start” treatments on new plaster and exposed aggregate finishes to accentuate the color or to remedy some discolorations. If those acid treatments aren’t causing plaster defects or discolorations, then on what basis do they claim that slightly aggressive water during Start-ups or afterwards causes all unsightly plaster problems?

Bottom Line: Using quality materials, including colorfast pigments, and superior workmanship will best ensure a durable and attractive pool finish for 20 years or more. That is what my father’s plastering company provided for their customers.

For photos of bleached pigmented plaster and more detailed information, click on these two links:


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The Art of Good Pool Plaster Color

The Art of Good Pool Plaster Color

An attractive plaster color (other than white) is often preferred by pool owners. However, it is very difficult for plasterers to produce a uniform and consistent color. The reality is that there will always be some minor shading (mottling) and variation in the color and can never be uniform looking like paint or fiberglass.

One of the primary reasons for non-uniformity is that pool plaster a hand-finished product. It is plastered by multiple finishers and subjected to a variable environment during curing. Most pools are also plastered using multiple batches of material which will never match precisely.

Pool owners need to accept that reality. In fact, the National Plasterers Council (NPC) appropriately recommends that a “Disclaimer or Waiver” be provided to pool owners to explain that there may be slight differences in the color shading.

Fortunately, quality-oriented plaster companies know how to produce a relatively good-looking color finish that will satisfy most pool owners. Along with other good practices, such as tenting pools to control temperature and humidity, they use colorfast pigments, a low and consistent water/cement ratio in all batches of material, they do not add any calcium chloride and do not add water to the surface during the troweling process. Lastly, they achieve a smooth finish with a properly-timed final troweling before the plaster becomes too stiff.

When the Color goes Bad

Obviously, poor chemical maintenance can either etch or scale any surface, including colored surfaces, but those are known and accepted phenomena. There are two non-chemical reasons for color problems developing with new plaster finishes, including quartz and pebble finishes. They are workmanship and materials.

When a pool is plastered too fast, due to adding too much calcium chloride set accelerant, the plaster surface can display severe and irregular mottling, color fading, or white blotchiness, streaking, and spotting. Also, if other quality workmanship practices, such as proper troweling, trowel pass timing, water/cement ratio, refraining from wet troweling or propane torching, etc. are not followed, increased negative effects may plague the surface aesthetics. And understand that those ugly discoloration problems generally take a few months to worsen and become increasingly visible.

Of course, a “Disclaimer or Waiver” document should be not used as an excuse by plasterers to avoid taking responsibility for their work quality.

The above discoloration issues are not caused by aggressive water. If it did, then colored cement driveways and walls (on buildings) would have similar results when rained upon (which is aggressive water). Yet, they do not because they are usually applied properly.

On other hand, overly positive LSI pool water can cause calcium scaling and can mask the colored plaster with a whitish deposit. When that happens, acid (aggressive water) treatments are often performed to remove the white discoloration and darken the plaster color again. Also, many quartz and pebble companies recommend maintaining the pool water slightly (LSI) aggressive to prevent the general whitening process from occurring altogether.

Therefore, aggressive water cannot be the cause when it removes the “white discoloration” and darkens the plaster color. And there are no plaster studies showing that slightly (LSI) aggressive pool water causes irregular white blotchiness, splotches, or streaking in colored (or white) plaster pools to appear in just a few months.

Evidence from plaster/cement petrographic “forensics” studies show the cause and effect relationships between color surface failure and improper workmanship practices. See this link for reports on this topic.

The Bottom Line

Good workmanship standards are needed for the pool plastering trade.


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The LSI is Reliable


We at onBalance have conducted several LSI experiments and have determined that maintaining a balanced LSI (-0.3 to +0.5) helps prevents scaling and prevent the etching of plaster finishes.

However, one plaster industry leader suggests that even when pool water is LSI balanced, if the alkalinity level is below 80 ppm (the industry’s Ideal minimum, not Operating minimum, which is 60), the pool water is aggressive and can discolor or damage pool plaster. Not so.

Anyone that is experienced in calculating the LSI knows that a low alkalinity can be offset by raising the calcium level and/or raising pH to keep the water balanced. To demonstrate and confirm that, we conducted several plaster experiments.

For example, two quality pool plaster coupons were made and cured in balanced water for 30 days.  At that point, one coupon was placed into water that had a low Total Alkalinity of 40 ppm, well below the minimum standard. The Calcium level was set at 350 ppm and the pH was maintained from 7.8 to 8.0, which off-set the low alkalinity and achieved a balanced LSI of about -0.1 to +0.1.

The other plaster coupon was placed into water with a low Total Calcium level of 90 ppm. The alkalinity was maintained at 130 ppm and the pH from 7.8 to 8.2, which together off-set the low calcium level and achieved a balanced LSI of about -0.1 to +0.3.

After six months in the water, the plaster coupons were removed from the water containers, and the water was tested for the calcium content to determine if any dissolution and etching of plaster surface material occurred. (An increase in calcium from the water’s starting point would indicate that calcium had been dissolved from the plaster coupon, which contains the only available source of calcium in this experimental set-up).

The result? There was zero increase calcium in either water container.

The results of this experiment are totally consistent with the concept of calcium carbonate saturation as published in the municipal water supply, as well as the swimming pool chemistry industries. The results demonstrate that even when the alkalinity or calcium level is low – below the APSP’s minimum standard – but the LSI calculation shows that the water is balanced, then the water IS balanced, and therefore, not aggressive. But understand, we aren’t recommending that maintaining low alkalinity or calcium hardness levels is the preferred way. This is just information to help pool builders and service techs confront false claims about water chemistry and various plaster problems.

The False Claim Regarding Aggressive Water

It is very unfortunate when new pool plaster surfaces sometime develop either gray mottling, white spotting and streaking discoloration, flaking (spalling), craze cracks, calcium nodules (from delamination), or other such defects, all of which are attributable to poor plastering workmanship, and yet, instead of advising the plastering company that improper plastering practices occurred, one NPC inspector (incorrectly) tells pool builders, service techs, and pool owners that aggressive water causes the above problems.

As mentioned above, the blame is often directed at low alkalinity or calcium hardness levels even though the actual LSI was balanced! But more importantly, the above listed plaster problems are NOT caused by aggressive water. Cement literature, empirical evidence, and even the NPC/Cal Poly/NPIRC study results demonstrate that.

Even when pool water IS aggressive, and etches plaster, it etches it uniformly, not in a mottled, spotted, or streaked pattern unless the plaster is non-uniformly defective as well.

It is our hope that pool builders, service techs, and pool owners will not be fooled by such non-sense. But it is happening far too often. Members of the onBalance team are often contacted regarding plaster problems, and we try our best to help them avoid being a victim of false claims.


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Pool Start-up Alternative for Plaster Pools

Orenda Technologies has recently unveiled a new start-up program that prevents the formation of plaster dust by adding calcium (calcium chloride) to low calcium tap water while filling brand-new plaster pools. We have received communications asking us if this calcium program is compatible with, or a viable alternative to the Bicarbonate Start-up Method that also prevents plaster dust.

The Orenda start-up program can, in certain situations, be an effective alternative to the Bicarb Start-up program which the onBalance team has been promoting for many years. It follows closely the principle of adjusting “aggressive” fill or tap water to a positive LSI number, preferably to about +0.5 for the filling of new plaster pools.

It is known that aggressive fill water is detrimental to new and vulnerable plaster finishes, including quartz and pebble, and can lead to plaster discoloration and deterioration problems developing afterwards.

Adding either calcium chloride or sodium bicarbonate to soft fill water will increase the LSI and will help prevent plaster dust and damage to new and (slightly) unhardened pool plaster. Under magnification, the plaster surface remains smooth, dense and hard, without etching caused by aggressive fill water. That in turn, will help plaster surfaces last and look good for 20 years or more instead of just 5 to 10 years before they start looking worn, deteriorated, and stained.

Both the Bicarb and Orenda “calcium addition” start-ups work by achieving a combined calcium and alkalinity content of at least 400 ppm (minimum) and up to 500 ppm of the fill water, and an LSI of +0.5. It is also important for the pH to be maintained below 8.4.

Orenda also claims that adding their chelating product SC-1000 during the start-up process helps prevent potential calcium scaling issues.

The immediate visible evidence that these start-up programs are superior to the Traditional start-up is by observing that there isn’t any plaster dust developing once the pool is full of water as is sometimes seen, even with quartz and pebble finishes. The Traditional start-up program as advocated by the NPC doesn’t require balancing the fill water until a day to two after the pool is full of water. That is too late. The damage has already occurred.

Click on the following video links to see the positive results of the Orenda start-up program:

As with most things, there are always variables to consider. If you are in an area where the calcium hardness level does not generally increase in your pools, then the Calcium addition start-up program would be a viable program to follow. However, if you are in an area where the calcium level does increase, and you want to avoid increasing it with chemical additions, then in our opinion, using the Bicarb start-up is preferred.

Click here to see the onBalance Bicarbonate Start-up page:

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How to Obtain a Quality Pool Plaster Finish

For pool builders, remodeling companies, and pool plasterers that want the best chance to obtain a quality and discoloration-free pool plaster finish (including white, color, and quartz aggregate pools), the link below is to an article in WaterShapes (a pool industry publication) that explains the preparations, workmanship, and practices to follow. 
Consider performing personal supervision on the entire process to ensure good results.

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Beginning in 2004, a series of plaster research studies were released by the National Plasterers Council (NPC), which they instigated and financially supported, and which were undertaken by the California Polytechnic State University in San Louis Obispo. In these studies, the researchers concluded that aggressive water conditions were the cause of “spot etching” and other plaster surface defects. The conclusions, and the quality of the research, have long been contested within the industry, yet the studies are still referred to by NPC plaster consultants as authoritative, at times to the detriment of innocent pool owners and service technicians.

In 2015, inorganic chemist Dr. Marcelle Dibrell peer reviewed Phase II of the Cal Poly research. She determined that the conclusions drawn by Cal Poly were not supported by their research, and that they did not prove what the researchers said they proved about plaster spotting.

This year Dr. Stan Pickens, also a prominent chemist and consultant in the swimming pool industry, independently reviewed Phase I of the Cal Poly research. Dr. Pickens was a member of the APSP Recreational Water Quality Committee for two decades, and served as its Chairman from 2014-2016.

Addressing the Phase I report, Dr. Pickens concluded: “While it is apparent that the study was a major undertaking, there are many problems with design study imbalance, flawed sample preparation, failure to control critical variables, and apparent lack of understanding of chemical principles relevant to water balance and sample preparation. These deficits call nearly all of the results and conclusions into question.”

Dr. Pickens also reviewed Dr. Dibrell’s critique of Phase II. In his review he states, “Dibrell’s conclusion that the experiment provided no reasonable explanation for the cause of ’spot etching’ is a reasonable one, since the reported etching did not correlate with the calculated LSI, and since general etching is not the same as spot alteration.” He adds “The occurrence of ‘spot etching’ in pools that – according to the data – were generally either balanced or scaling does call aggressive water into question as a cause. It appears that the Cal Poly researchers were predisposed to find aggressive water as the primary cause of spot etching, regardless of what the data showed.” He also includes the fact that Dr. Dibrell could have pointed out many additional deficiencies in the Cal Poly Phase II report, but notes that “perhaps [she] was too polite to point out the glaring deficiencies in the Cal Poly data.”

Dr. Pickens reviewed another interesting publication.  Apparently at the same time Dr. Kachlakev of Cal Poly was telling the pool industry that they had proven the cause of “spot etching,” he and Dr. Pal (the project’s chemist) and Dr. Rothstein (the project’s petrographer) went to the International Cement Microscopy Association (ICMA) annual conference and presented their material to their petrography peers. But in that setting, they admitted that they did not nail down the cause of “spot alteration.” 

The onBalance group is calling upon the NPC and Cal Poly to retract these invalidated studies in light of Dr. Dibrell’s previous review and these current critiques from Dr. Pickens.

In addition, onBalance is calling upon the NPC to acknowledge that the million-dollar Cal Poly study (and other NPC-associated studies) have not only failed to prove aggressive water is the cause for plaster spotting, but also failed to show that aggressive water chemistry causes gray mottling discoloration, calcium nodules, craze cracking, and spalling/flaking as has been suggested by plaster consultants. They have failed to do so because it simply isn’t true.

Dr. Pickens’ peer reviews may be viewed at

Note: This winter, onBalance is constructing their own plaster demonstration pools. They will be investigating parameters including aggressive vs. balanced water chemistry, various levels of calcium chloride set accelerant in pool plaster, and the effects of low-level chlorination vs. regular super-chlorination on organic vs. inorganic color pigments. They assure the industry that this type of testing can be done without the failures found in the Cal Poly process.


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The Future for pH and Chlorine Standards

It appears that the pool industry’s long-time recommended parameters for chlorine and pH levels will be changing in the near future.

The current range of 1 to 4 ppm for chlorine will likely be raised when pool water contains cyanuric acid (CYA), and the pH range will be broadened beyond the current limited range of 7.2 to 7.8. The reason for this change is due to a new understanding of the science of stabilized pool water.

Some years ago, Richard Falk (known as Chemgeek on pool forums) wrote about the relationship between CYA, Chlorine, and pH, and communicated that information to the Council for the Model Aquatic Health Code (CMAHC) that adopts standards for public and commercial pools. As a result, two years ago the CMAHC formed an Ad-Hoc committee with Ph.D. chemists, micro biologists, and other knowledgeable industry members to study that topic.

At the recent World Aquatic Health Conference in October, Richard Falk, representing the CMAHC Ad-Hoc committee, presented scientific data regarding the benefits of CYA and on the chlorine/CYA/pH equilibrium relationships, including bacterial kill rates, and other factors affecting pool sanitizing by chlorine when CYA is present.

To summarize, the CMAHC is tentatively suggesting higher minimum amounts of Free Chlorine should be maintain and proportionately based on the amount of CYA present in pool water. For example, at 40 ppm of CYA, the minimum Free Chlorine level should be at least 2 ppm, and at a CYA level of 90 ppm, the minimum chlorine level should be 4.5 ppm.

It should be noted that the CMAHC is aware of the EPA’s chlorine regulation minimum of 1 ppm and maximum of 4 ppm. However, the CMAHC believes that higher Free Chlorine levels are necessary to achieve safer and healthier pool water. Also mentioned was that a higher pH (above 7.8) does not significantly affect chlorine efficacy (killing power) when CYA is present.

It was clear from statements made by various CMAHC and CDC representatives that standards should be adjusted or changed as science becomes better understood. They also emphasized that flexibility in standards are needed (when scientifically supported) to allow more effective water maintenance.

At some point, the CMAHC and CDC will probably present this science to the EPA in hopes that higher chlorine levels will be adopted when CYA is present. And a broader pH range (due to applicable science) may be forthcoming also.
For more information and a simplified explanation of the science regarding Chlorine/pH Efficacy when CYA is present in pool water, see this link:

Dr. Stan Pickens (Ph.D. and water chemistry consultant) has also written a very detailed and scientific paper on “Relative Effects of Chlorine and pH on Disinfection” which will also be available to read.

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Announcement of Pool Plaster Study

The research and consulting group onBalance has decided to conduct new plaster research studies to generate additional evidence regarding the cause of unsightly plaster discolorations and defects. The plaster issues of concern are gray mottling discoloration of white plaster, white spotting of both colored and white plaster, calcium nodules, spalling, flaking, and craze-cracking.

One aspect of the study will be to construct two demonstration pools, each with sections of various plaster formulations (color and white) and subject them both to aggressive and balanced water. The entire plastering process will be video-taped, and the ongoing water maintenance and monitoring will improve upon previous studies performed Cal Poly (NPIRC).

Although forensic studies and other evidence have already documented the above plaster/cement problems are caused by various improper material and workmanship issues (and not aggressive water), the onBalance group will move forward with this project because the National Plasterers Council (NPC) leaders won’t acknowledge that this science and evidence exists.

To date, onBalance has had failed white spotted (on both white and color) pool plaster analyzed by various professional cement petrographers a dozen times. In all cases, improper materials and finishing practices were identified as contributors to causing extremely porous and soft white spots (aka “spot etching”). Not a single study implicated LSI aggressive water chemistry as the cause. The consensus was that white spotting is not etching.

There is also an abundant amount of cement science and studies that has documented that graying, cracking, spalling, spotting, and efflorescence of cement surfaces involve poor materials, poor mixing, or poor workmanship practices; not by external water. If aggressive water caused the above problems, then all cement sidewalks should soon result with all those abnormalities when rained upon.

But to be clear, it is well-known that aggressive pool water will uniformly etch a plaster surface, and that overly saturated or hard water will deposit calcium scale onto a plaster surface which eventually discolors.  Etching or scaling are not a plaster defect.

For their part, it is unfortunate that the NPC has published “fake news” regarding the Cal Poly (NPIRC) test pool results, and some plasterers claim that aggressive water causes all the plaster problems mentioned above.

NPC leaders have been very silent after an independent 2015 review by a chemist (Dr. Marcelle Dibrell of Service Industry News) exposed that the NPIRC results DID NOT prove that water chemistry caused white spotting or spot etching. When honestly evaluated, the Cal Poly research actually serves to exonerate aggressive water chemistry as causing white spotting, gray mottling discoloration, calcium nodules, spalling, flaking, and craze cracking.

The NPC has also been silent regarding a published admission (2005) by the Cal Poly professors and a professional cement petrographer that the NPIRC Phase I study did not prove any specific causations (whether from chemistry or construction practices).

It is not surprising that NPC leaders won’t meet with the onBalance group to review and analyze the NPIRC study reports and forensic studies and analysis.

The bottom line is that NPC leaders are perfectly willing to remain silent about the science and keep everything unresolved. Why? Because they often win with that situation. Their plaster inspectors can inspect plaster problems, and easily convince unsuspecting and innocent pool owners and/or service techs (with false information) that aggressive water causes all those plaster problems. Even pool builders and material companies can be intimidated by them.

And in regards to onBalance’s new plaster study projects; there will be a written “study protocol” provided to the industry for comments and suggestions before the demonstration pool project is started.

Donations are needed to help fund this project.  IPSSA Region 7 Table Top committee has pledged up to $10,000 of matching funds for this ongoing project, and many service techs are contributing.  Plaster materials and various pool equipment has also been pledged from various companies to help fund this project.

The onBalance group is confident that this project will soon provide important and additional evidence in understanding the plaster problems identified above. 

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The Reality of Pool Chemical Treatment

For at least 40 years, many pool service companies have been successfully maintaining their residential pools on a once-a-week visitation basis. Empirical evidence has shown that pool water can be kept safe and properly sanitized without harmful bacteria and algae developing with weekly treatment programs.

Also, pool service companies provide a great service by keeping hazardous chemicals out of the hands of pool owners and their children.

One reason that pools can be kept properly sanitized with weekly visits is due to the use of various feed or auto-systems which usually use either bleach, Cal hypo, Salt, Trichlor, or bromine for sanitizing.  And of course, the use of Ozone and UV systems also keep pool water safe without daily treatments.

The use of cyanuric acid, which slows down chlorine loss, also helps to provide the ability for less frequent chemical treatments.  In fact, there are no reports or studies that suggest that professional once-per-week treatments automatically result in unsafe, cloudy, or algae pool water conditions.

Another important aspect of maintaining a good chemical and sanitizing program for residential pools is maintaining the pH within a proper range.  One thing that worries some service techs is when pH drifts higher in the days between service visits.

In that regard, some service techs and others in our industry seem to believe that a pH of 8.0 to 8.4 makes chlorine in pool water completely ineffective and unable to properly sanitize and kill bacteria and algae. It is also incorrectly taught that eye and skin irritation develops at these pH levels.  Both of those concepts are not true.

It is well known that CYA reduces the amount of “active” hypochlorous acid (HOCl) in the water.  But what is not well-known is that when the pH rises slightly in pools containing CYA, the amount of HOCl almost remains the same, and therefore, has nearly the same sanitizing efficacy and bacteria killing power.

In 1974, a report written by J. E. O’Brien indicated that when the pH rises from 7.5 to 7.8, the reduction in HOCl only drops by about 10%, and when the pH rises from 7.8 to 8.2, the reduction in HOCl only drops by 10% also.

But is that the end of the story?  What about that lower amount of active chlorine? Is the water unsafe? While a 10% lower amount of HOCl wouldn’t make a lot of difference in sanitizing, the lower amount of HOCl can be easily compensated for and overcome by simply maintaining the chlorine 10% higher.

For example, pool water with 2 ppm of chlorine, with 50 ppm of CYA, and at a pH of 7.8 is considered acceptable by industry standards.  All one needs to do to obtain the same killing power and chlorine efficacy when the pH is maintained at 8.2, is to raise the chlorine level by 10% or to 2.2 ppm.  Obviously, that isn’t very much additional chlorine in a 15,000-gallon residential pool.  Only about 3.2 ounces of pool bleach.

Let’s also understand that if the chlorine is at 3 ppm in the above example with a pH of 8.2, it means that there is more sanitizing (killing) efficacy than having the chlorine at 2 ppm with a pH of 7.5, or even at a pH of 7.2.  This example shows that pool water can be better sanitized at a pH of 8.2 (due to higher chlorine levels), and a higher pH does not automatically render chlorine incapable of killing bacteria and algae.

Plus maintaining the chlorine level a little higher results in a higher reservoir of OCl- ready to convert into the more active HOCl.

Finally, studies have shown that a pH of 8.0 to 8.4 alone does not cause eye and skin irritation. So service techs can stop fretting about a pH rising above 7.8 between visits. In fact, many pool service companies have been successfully maintaining the pH from 7.8 to 8.2 for many years.

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What Alkalinity is Best for Pools?

It is amazing how incorrect information gets started, and gains traction despite being wrong, and not based on science. For example, contrary to some pool literature and manuals, it has been shown that a pH of 8.0 to 8.4 is workable, and sometimes is best for some pools.

Another misconception regarding pool water maintenance involves the recommended “Ideal” alkalinity range of 80 to 120 ppm. While that may be a good range for some pool situations, it is not necessarily the best when using alkaline or pH increasing sanitizers.

It is unfortunate that pool manuals suggest that maintaining a high alkalinity range of 80 to 120 ppm is needed to keep the pH “stable.” That statement leads to a misunderstanding.

No, the pH is not stable at 7.4 or even 7.6. Instead, for many pools, depending on the sanitizer being used, the pH generally “wants” to rise to 8.2 - 8.4 when the carbonate alkalinity is 80 to 120 ppm. That is where the pH is “stable” at.

The part that is true about higher alkalinity ranges is that when adding small amounts of acid, the pH doesn’t lower significantly. Every service tech knows that when the alkalinity is high, it requires a lot more acid to lower the pH.

At these higher alkalinity levels, once acid is added to a pool and the pH is lowered to 7.2, the pH will immediately begin to rise back up rapidly due to carbon dioxide off-gassing. In fact, with an alkalinity of 100 ppm (carbonate), it is not uncommon that the 7.2 pH can typically rise to 7.6 within 24 to 36 hours depending on various factors.

As the pH rises, the speed of the rebound slows down. With 100 pm of alkalinity, a pH of 7.6 typically takes about 3 to 4 days to rise to 8.0, and up to 8.2 and perhaps 8.4 in the days following. Again, the speed of pH rise depends on various conditions.

(There are exceptions to the above situations of the pH rising quickly, and one is when using an acidic sanitizer, such as Trichlor tabs. And we will address that issue later).

Now let’s address an interesting fact about adding acid to lower the pH from 8.0 to 7.2. It only requires half as much acid to lower pH from 8.0 to 7.6 as it takes to lower the pH from 7.6 to 7.2. For example, at 100 ppm of (carbonate) alkalinity in a 20,000-gallon pool, it requires about 20 ounces of acid to lower the pH from 8.0 to 7.6. But it will require double the acid (about 40 ounces) to continue lowering the pH from 7.6 to 7.2, for a total of 60 ounces.

When adding the extra 40 ounces of acid to lower the pH from 7.6 to 7.2, about 8 ppm of additional alkalinity is consumed, and the pH only remains below 7.6 for about a day or so. Also, about 2.2 pounds of sodium bicarbonate will be needed to restore the extra lost alkalinity.

Therefore, service techs are faced with a choice. Do they add more acid to lower the pH to 7.2, or not? Other than when you are intentionally lowering a high alkalinity level, does it make sense to add the extra acid just to lower the pH past 7.6 and to 7.2 when it will be 7.6 again within a day or two? 

Of course, some will say that it is a good idea to always lower the pH to 7.2. Although for some situations it is a good idea, we suggest that it is not always a worthwhile thing to do.

Fortunately, one of the greatest developments by test kit manufacturers was producing the “Acid Demand” test feature. No longer do service techs need to guess how much acid can be added, or needs to be added, in order to lower the pH exactly to where they want it. Additionally, having that capability allows for maintaining a lower alkalinity (than the recommended Ideal parameters) without over-dosing with acid and causing the pH to go too low.

An Alternative Program

Pool manuals and literature also (incorrectly) state that an alkalinity of 60 ppm causes the pH to be unstable and erratic than when the alkalinity is higher. Again, that is incomplete and misleading. When no acid or very little acid is being added, the pH can be very stable, even at pH levels lower than 8.2 - 8.4 which occurs at higher alkalinity levels.

That can be very beneficial, and the Acid Demand testing feature can help service techs avoid over-treating with acid.
Here are some interesting facts about alkalinity. If pool water contains only 20 ppm of (carbonate) alkalinity and no additional chemicals are added (and if there are no other mitigating influences), the pH will slowly and eventually rise to a pH of about 7.8, given enough time. To have the pH stable at 7.5, the alkalinity would have to be just 10 ppm. Isn’t that amazing!

Of course, 10 ppm and 20 ppm of alkalinity is far too low and risky for swimming pools, especially if acidic sanitizers are being used. But let’s understand that the lower the TA, the slower the pH will rise, and the lower the level the pH will rise up to.

Now let’s get practical, and apply some of this chemistry. Consider maintaining an alternative alkalinity level or range for certain pools. Instead of keeping the alkalinity at 90 to 120 ppm, let’s consider lowering it to 60 to 70 ppm for pools that use bleach, calcium hypochlorite, or salt generator systems as the primary sanitizer. Those three chlorine sources also generally cause a slight increase in the pH, in addition to the natural pH rise due to carbon dioxide off-gassing.

With 60 ppm of carbonate alkalinity, the pH doesn’t want to climb to 8.4, but only to about 8.0 to 8.2 instead. Additionally, the speed of the pH rising with 60 to 70 ppm of alkalinity is slower in comparison to maintaining an alkalinity of 90 to 120 ppm. It will take about 2 to 3 days for the pH to go from 7.2 to 7.6. And then it will take about another 5 to 7 days to rise to 8.0. That is several days longer than what occurs when the alkalinity is around 100 ppm. (Again, there are additional variables and situations that affect the speed of the pH rising).

Another benefit is that at 60 ppm of alkalinity, it requires less acid (about 12 ounces) to lower the pH from 8.0 to 7.6, than with 100 ppm of alkalinity (about 20 ounces of acid). That also means that less sodium bicarbonate will be needed to restore the consumed alkalinity if needed.

Many service techs consider this pool water balancing program to be more manageable, reasonable, and productive with once-a-week chemical treatments. They also know they should keep the water LSI balanced (-0.3 to +0.5) at all times. According to the LSI, maintaining a slightly higher pH allows for maintaining a slightly lower alkalinity level. Pool water can still be LSI balanced with those adjustments.

As mentioned before, the Acid Demand test feature provides the mechanism and ability to closely monitor and adjust the pH with smaller amounts of acid, and at a lower alkalinity level.

Different Pool Conditions Benefit with Different Chemistry Programs

The effectiveness of some sanitizers, such as Ozone, UV, Bromine, and PHMB isn’t hindered by a slightly higher pH. For those sanitizers, the alternative program of maintaining a lower alkalinity of 60 to 70 ppm and a higher pH of 7.8 to 8.4 can be easier to manage. At that alkalinity and pH range, the pH can be fairly stable within that range, and that means that less acid/bicarb treatments are needed.

And as was stated in a prior email update, maintaining a higher chlorine level (2 ppm and above) allows for maintaining a higher pH of 7.8 to 8.4 with completely adequate sanitizing efficacy.

There will be some who would object to a suggested “Ideal” alkalinity range of 60 to 80 ppm. Yet, 40 years ago, the chemists at Olin Chemical stated that the “optimum” alkalinity range is 50 ppm to 100 ppm. That is a lower range than the current recommended ideal alkalinity range of 80 ppm to 120 ppm.

So why does the pool industry recommend a higher alkalinity range? Maybe it has something to do with the increased popularity of Trichlor in the 1970s-1980s. Since it is an acidic sanitizer (as opposed to previously more popular base sanitizers such as bleach and Cal hypo…), when using Trichlor, a higher alkalinity should indeed be maintained in order to buffer the pH of the water better. A benefit of trichlor is that it lowers the pH and counters the natural pH rise. A negative is that it increases the CYA and slows down the kill time of the chlorine.

In fact, in some situations a higher alkalinity than even 120 ppm may be needed to prevent the pH dropping below 7.2 when adding acidic products. This includes some non-plaster pools, such as vinyl and fiberglass surfaces, some areas of the country where a lot of “acid rain” falls in a short period of time, or even some pools that have pool covers installed.

But as has been shown for some other pool situations, a lower alkalinity level can be more effective to manage and stabilize the pH. Therefore, depending on various situations, some pools might have the pH from 7.2 to 7.6, and other pools do better with a higher pH of 7.8 to 8.2.

Also, according to the LSI, maintaining a slightly higher pH allows for maintaining a slightly lower alkalinity level. Pool water can still be in perfect balance (-0.3 to +0.5) with those changes.


Due to the above variables and situations involving all swimming pools, we suggest that the “Ideal” recommended levels be dropped, the LSI be emphasized, and allow our knowledgeable service techs to adjust the water chemistry parameters in their pools that can result in a more effective balanced and sanitized water.

Currently, the APSP is developing a new water chemistry standard for residential pools. Now is the time to modernize and correct the old material that is in need of an update. Service technicians have much to contribute to the process, rather than relying on old and occasionally incorrect information. Now is the time to create standards that can withstand scientific and reasonable scrutiny – and allow for us to work smarter rather than merely “the way it has always been done…”

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What pH is Best for Pools?

Experienced service techs know that the pH in many of their pools generally rises above 7.8 within four to seven days following chemical treatments.  It is a chemistry reality that when water contains 80 ppm to 120 ppm of carbonate alkalinity, and is left alone and untreated by additional chemicals, the pH will rise to 8.0, and sometimes as high as 8.4 and stay there until chemically treated again. 

What does this mean?  It means that thousands upon thousands of residential pools are not kept within the (APSP-recommended) pH range of 7.2 to 7.8 on a constant basis. This has been true ever since pools starting getting built in residential backyards many years ago.  Yet, there is no indication that unsafe conditions or other problems have resulted from that fact. 

However, for the past 50 years our industry’s chemists, class instructors, and trade associations have been advocating to service techs that a pH above 7.8 is wrong, unsafe, automatically unbalanced, and causes various problems. Is that true, or not?

How Standards Got Started 

Let’s consider what happened 50 to 60 years ago that probably influenced our industry to adopt the restrictive pH range of 7.2 to 7.8 as our standard.

At that time, calcium hypochlorite (Cal-hypo) and sodium hypochlorite (bleach) were the primary sanitizers for residential pools.  It was observed that adding Cal hypo or bleach to pool water with a pH of 8.0 to 8.2 would sometimes cause cloudiness.  It was also observed that maintaining a pH of 7.2 to 7.8 and a lower alkalinity helped reduce cloudiness when those sanitizers were added.

So it makes sense that some in our industry promoted the concept of keeping the pH at a lower range of 7.2 to 7.8 and the alkalinity below 180 ppm to avoid making pool water cloudy. 

However, for some reason, what started out as a reasonable standard for bleach and Cal-hypo pools a half-century ago got out-of-hand, and our pool industry has ever since been (incorrectly) taught that a pH above 7.8 automatically causes cloudy water and scaling conditions, causes eye and skin irritation, and that pool water at higher pH levels cannot not be properly sanitized with chlorine no matter what.  And those same false claims were also applied to alkalinity levels above 180 ppm.

In all fairness, those recommended levels may be a good standard when using those alkaline sanitizers and in hot weather areas – but not necessarily for all other pool products and other pool conditions.

The fact is that the pH of pool water can be easily maintained at 8.0 to 8.4 without either cloudiness or scale. At the time the standard was introduced the Saturation Index was not commonly used in the industry, but now it is regularly used and understood.  Simply maintaining the water within a balanced LSI range is all that is required to avoid cloudiness or deposits from calcium precipitation.

Also, there are studies that show that eye irritation does not develop until the pH rises above 9.0 or is below 7.0. This is consistent with the EPA drinking water standard, with high pH eye drops for soothing irritated eyes, and in fact higher pH levels even lead to less irritation from chloramines when they are present.  Yet current APSP literature still contains the listing of incorrect consequences of high pH and alkalinity.

With the availability of other chemicals and new technologies, including acidic or near-neutral chlorine sanitizers such as Trichlor and Dichlor, our current industry’s chemists, associations, and those who are writing our standards should consider modernizing the chemistry parameters for all pool situations and conditions.


How to Achieve Good Chlorine Efficacy

In addition to water balance, let’s examine the most important aspect of pool water treatment, which is keeping pool water properly sanitized and safe for swimmers.  This topic has also been misunderstood. 

Again, for fifty years, many seminar instructors have stated something like “high pH makes chlorine less effective, or at high pH, chlorine is not powerful enough to get the job done.”

Many who hear that incomplete statement end up believing that no matter what, high pH prevents effective sanitizing by chlorine, and that there is nothing that can be done to overcome this “fact.”  But that would be the wrong conclusion. 

The following question should be asked: is it possible to achieve sufficient and effective sanitation with a pH above 7.8?  The answer is yes.  All one has to do is to increase the chlorine level slightly higher to achieve the same amount of chlorine efficacy and effectiveness. How easy is that?

For example, let’s start with pool water that has a pH of 7.8, and contains 1.0 ppm of chlorine, which is an “acceptable” amount of chlorine efficacy according to industry standards.

If the pH of pool water is 8.2 (which often happens in many pools), all that is needed to achieve the same chlorine efficacy is to increase the chlorine level to 2 ppm.  That’s it; just add an extra 1ppm of chlorine.  That would match the chlorine efficacy of 1.0 ppm at pH 7.8. 

This means that there is the same amount of hypochlorous acid (HOCl) at a pH of 8.2 with 2 ppm of total chlorine as there is at pH of 7.8 with 1 ppm of total chlorine.  And of course, maintaining the chlorine residual above 2 ppm provides a greater amount of chlorine efficacy, including more in reserve for long-term sanitizing.

Let’s also understand that as the more active chlorine (hypochlorous acid) gets used up by killing bacteria and algae, the less-powerful hypochlorite ion will start converting over to hypochlorous acid very quickly, and therefore, soon becomes the more powerful type (hypochlorous acid).  The hypochlorite ion does not remain as hypochlorite forever, which is sometimes misunderstood. 

Interestingly, sanitizers such as ozone, UV, and PHMB (biguanide) are not affected by a high or low pH.  Bromine efficacy is still considered effective at a pH of 8.4.  So why is there a restrictive pH range of 7.2 to 7.8 for those products?

So can there be adequate sanitizing efficacy and a good margin of safety when maintaining a pH of 8.2 or even 8.4?  Absolutely.  The science shows that and so does empirical evidence.  So why limit the available options of providing properly sanitized swimming pool water for our consumers?


Flexibility is Needed

While we are on the subject of allowing higher pH levels for swimming pools, it is interesting to note that there are water municipalities that provide tap water with a pH in the range of 8.8 to 9.3 to millions of residents.  Yes, that is correct, and they add about 2.0 ppm of chloramines for sanitizing. That water is safe, and does not adversely affect people who ingest or bathe in it.

Even the PhD chemists at Olin Chemicals 40 years ago wrote that a pH of 7.2 to 8.4 was non-irritating to the eyes, and was more of a concern when the pH is below 7.2.

Another point is that many service techs (and even self-maintenance pool owners) have been following the Jock Hamilton Index, which recommends maintaining the pH at 7.8 to 8.2, and they have been successful at doing this for many years without problems.

Since the pH of pool water generally wants to rise to 8.0 and often up to 8.4 (assuming a moderate alkalinity), and since that pool water can be properly balanced and sanitized, without eye or skin irritation, and without cloudiness, why not allow service techs to maintain pool water at a pH of 8.0, 8.2, or even 8.4 when they are using a non-alkaline sanitizer?

Why are restrictive standards being imposed that may make maintaining pool water more difficult, cumbersome, and complicated in certain conditions?  There can be easier and more effective ways to maintain pools, and not only is that possible, it is the way many experienced service techs and pool companies are maintaining their pools today, and have been for over 40 years.

This is not the first time that service technicians have pointed out that chemical experts could use a little advice or even correction. Service professionals demonstrated that the “Acid Column” technique was a myth, and it was service professionals who corrected the industry’s dosage charts for acid and baking soda.


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What is the NPC up to?

Some plasterers are occasionally finishing pools so fast that it detrimentally affects the quality and durability of plaster surfaces, and are not even aware of the consequences. And the NPC is enabling for this to happen. This needs to stop. Improper practices can speed up the finishing process, but they also lead to a short life-span for plaster, lasting only five-ten years instead of twenty. They are not doing the consuming public right by condoning, and by omission endorsing, those improper practices.

Even worse, combining improper practices to the point of being excessive can lead to plaster defects, deteriorations, and discolorations showing up on plaster surfaces (including quartz and pebble) within a couple of weeks to one year of time.

Last year, NPC board members assisted in writing and approving an ANSI Plaster Standard that did not include specifications, limits, or warnings about the amount of water being added, calcium chloride content, excessive wet troweling or late hard troweling. That is irresponsible. Are there no such things as improper workmanship practices that cause early deteriorations? Is it the purpose of this document to protect plasterers from being held responsible for causing defects and discolorations?

Yet, back in 1998, NPC acknowledged (in their Technical manual) that improper practices cause calcium nodules, spalling (flaking), severe craze cracking, and hydration (graying) of white plaster.

But that changed in 2002 when new NPC leadership took over wrote a new Technical manual. The correct information on the causes of the above plaster defects were removed, and now NPC literature and consultants suggest that “aggressive water” causes those defects.

Essentially it is being suggested that if pool water has an alkalinity of 70 ppm or an LSI of just -0.1, then that is deemed as “out-of-balance” or “aggressive water” and causes plaster defects. That would be wrong, and there is no factual basis to claim that; but blaming service techs and pool owners for these problems happens often.

Let’s note that the American Concrete Institute (ACI) and Portland Cement Association (PCA) do not blame rain water (which is significantly aggressive) for causing the above defects on cement surfaces. Instead, they cite improper workmanship and/or material additives as the causes.

In 2003, IPSSA and others wrote to the NPC requesting the supporting documentation for the changed positions on those plaster problems. The NPC responded that they would not provide any evidence for the new Tech Manual changes, and that there would be no further discussion or debate.

The NPC then decided to conduct test pool studies at Cal Poly/NPIRC to try and prove their theories. But just like their similar studies conducted during the 1990’s, the results didn’t turn out the way they had hoped.

The 2004-2007 test pool studies showed that aggressive water did not cause the above plaster defects, including ”spot etching” (white soft spotting), which indicated improper practices was the likely culprit. But the NPC did not acknowledge that and misled our industry on what happened at Cal Poly. Now the NPC wants to do even more test pools instead of admitting to and abiding by those documented results.

It is readily apparent why the NPC refuses to sit down with anyone and discuss the Cal Poly results, and no longer sell the four full (100+ page) reports (Phases 1, 2, 3, & 4) from Cal Poly/NPIRC.

The NPC should be acknowledging what has been proven by their own Cal Poly/NPIRC studies (and documented by an independent peer-review), and the science and findings by professional cement authorities (who are experts in forensic analysis) that have identified improper practices that lead to early deterioration, discoloration, and plaster/cement defects.

The NPC should be promoting quality workmanship and start teaching their members the correct information about proper and improper plastering practices at their yearly conferences and in their Technical Manual. Until then, poor workmanship will result and be empowered, and uninformed service techs and pool owners will continue to be misled and victimized when plaster problems occur.

Sadly, our industry is letting (and in some cases, helping) the NPC get away with this agenda.

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Pool Service Techs: Don't Get Hoodwinked

Imagine, service techs: from day one, you maintain the pool water in perfect balance, yet get blamed for causing various plaster discolorations or defects. That is not a pleasant thing to deal with, especially if you are being told to pay thousands of dollars to re-plaster the pool.

Yes, some plastered pools (including quartz and pebble finishes) may develop either white spotting and streaking, calcium nodules, gray mottling discoloration, spalling (flaking), severe craze (check) cracking, or early deterioration within a few months after being plastered, and service techs or pool owners (or whoever maintains the water) have been incorrectly blamed for those plaster problems.

Generally, it will be claimed that the pool water has been “aggressive” at some point in time, even if the water has never been aggressive.  But more importantly, the above plaster problems are not caused by aggressive water.  Cement and plaster studies have identified improper workmanship practices as leading to those problems developing.

So why are these unfair accusations happening?  One main reason is because the National Plasterers Council (NPC) doesn’t do anything to stop it, and in some ways, enables it to happen.

Let’s examine this issue.  The NPC and some plaster inspectors define “balanced” pool water within very narrow parameters, but without any supporting science to back it up. The NPC states that all water parameters (pH, TA, CH) must be maintained within the APSP’s “Ideal” ranges to be considered balanced, and disregard the APSP’s “minimum and maximum” standards. On what basis do they require that?

For example, NPC literature essentially suggests that pool water with an alkalinity of 70 ppm is considered to be out of balance and aggressive, even though the APSP has established 60 ppm as the minimum alkalinity standard.  Even if the other water parameters make the LSI balanced, the NPC still considers that water “aggressive” and able to cause plaster problems.

Yet, contrary to that, the NPC says it is okay to use “acid treatments” on new plaster surfaces to remove stains and discolorations as a remedy.  Yet, acid treatments are 10,000 times more aggressive (-4.5 LSI) than pool water with an LSI of -0.2 which the NPC claims is too aggressive.

And it doesn’t stop there. There are plaster reports that falsely blame high CYA, high TDS (salt pools), Trichlor, high chlorine, carbonation, or ionizers for the some of the above plaster problems.  Again, the NPC has no science or study that supports such claims.  Even rebar (rust) staining has been claimed to be caused by “imbalanced” water chemistry.

So if you as a service tech are being blamed for causing one of the above plaster problems, and a NPC inspector or plasterer gives you a copy of the NPC Technical Manual, a report by Arch Chemical or Cal Poly (NPIRC), or any other literature, and suggests that it proves whatever it is they are claiming; don’t be hoodwinked or intimidated.  Those reports don’t prove that out-of-balanced water causes those problems. In fact, they mostly prove the opposite.

Also, if your chemical start-up process is questioned by the plasterer because the tap (or fill) water was aggressive, we suggest that it is the plasterer’s responsibility to see that the tap water is balanced before it used to fill the pool. Let's understand that the vast majority of the damage (uniform etching) that is caused by aggressive tap water occurs while the pool is filling; and before you show up at poolside (after it is full) to balance the water.  

So while the NPC leaders seemed to be focused on blaming water chemistry (outside very narrow parameters) for various plaster problems, they are also refusing to adopt simple and general workmanship standards and limits on plastering practices to ensure quality, discoloration-free, defect-free, and long-lasting pool plaster.  Very important issues such as water/cement ratio, wet troweling, late hard troweling, and calcium chloride limits, are not even mentioned in their new ANSI Plaster Standard.

Sadly, some plasterers currently advertise that plaster only lasts 5 to 10 years. But not long ago, plaster used to be promoted as lasting 20 years.  In reality, it still can and does last 20 years when quality workmanship is performed.  It’s not difficult to figure out who benefits and who is harmed when plaster finishes don’t last very long.

It is unfortunate that poor quality plasterers are being aided to avoid being held responsible for bad plastering work and results. That needs to change for the betterment of the swimming pool industry.

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Plaster Spotting Exposed Again

The swimming pool publication, Service Industry News and its’ PhD chemist, recently peer reviewed the NPC/Cal Poly (NPIRC) Phase 2 pool plaster study report and concluded that white spotting (soft spots, spot etching, and spot alteration) of their plaster pools was not caused by aggressive water, and that the claims (by the NPC) regarding that study are false. In fact, every plaster study of the past twenty-five years has exposed that the NPC is wrong, and that aggressive pool water does not cause spotting.

Back in 1991, some plasterers thought they had proven their theory with the NPC Arizona test pool and published that in a Pool & Spa News article. But later, after they were shown contradictory evidence, and that the Pasadena test pool (in partnership with IPSSA) showed completely opposite results, the NPC people would not concede the matter or answer any questions regarding those two test pools. The NPC then proceeded with more test pools.

When those test pools didn’t prove what the NPC had hoped for, they decided to do a plaster “coupon and alkalinity” study in partnership with us (onBalance) in 1999. Again, to the disappointment to the NPC, that experiment also showed that aggressive water had nothing to do with causing spotting. The NPC promptly disavowed that study.

At the NPC conference in 2000, we (onBalance) presented forensic evidence and findings by a prominent cement lab that plaster spotting (on actual failed plaster pools) was the result of improper plastering practices. The NPC did not comment or address those findings, but some members chose to criticize us (the messengers) personally.

The NPC then decided to retain Cal Poly University to conduct plaster studies starting in 2003. The NPC announced that this would be the final and end-all study, and promised that they would abide by the results. A year later, the NPC began claiming that their NPIRC study had proven that aggressive water caused spotting. But as it turns out, they were ignoring the serious problems with their conclusions.

In 2011-2012, three prominent cement labs studied plaster spotting, was peer reviewed by a fourth lab, and it was again confirmed that improper plastering was the cause. And as mentioned above, Service Industry News recently determined that the NPIRC study did not prove what the NPC claimed it did. So it is not surprising that the NPC has not been willing to meet with industry members to discuss (or debate) the NPIRC study results and the lab findings.

It appears that once the plasterers (incorrectly) publicized that the Arizona test pool study had proven their “aggressive water theory,” there was no turning back. One misrepresentation led to another. No one wants to admit to their peers that they were wrong in the first place.

Will the NPC ever acknowledge what the past plaster studies have determined? Will they abide by the past test pool results? Apparently not. Instead, they desperately want to do more test pool studies, and have even tried to drag us into it again. And amazingly, the water and plaster conditions proposed for the new joint study has already been done at the NPIRC, and they know what the results were!

The Pool Industry is tired of this three-decade controversy.  Isn't it time that the NPC end this charade?


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NPC & Color Plaster

If NPC leaders would just acknowledge what improper plastering practices do to pool plaster, there would not be a controversy within the industry - and there would be fewer plaster defects and discolorations occurring.

Case in point: Adding calcium chloride (hardening accelerator) to plaster and water troweling enables pools to be plastered faster and easier. But adding calcium chloride (CC) to a color pigmented plaster can also lead to blotchiness and mottling, which pigment manufacturers and the Portland Cement Association (PCA) warn about.


Even the Cal Poly/NPIRC test pool studies on color pigments provided confirming results. Test pools that had only one percent CC added to the colored plaster sections had significant discoloration. How can the NPC leaders ignore and not acknowledge this information to their own members?

The PCA also warns that adding water to the plaster surface while troweling also contributes to streaking, blotchiness, shrinkage cracks, and early surface deterioration.

Amazingly, the NPC/APSP writing committee refused requests to warn against the use of CC with color plaster in the new Plaster Standard, and stated that “the issue is simply one of aesthetics, and not durability.” So plaster discolorations don’t matter and are acceptable? And it does negatively affect durability also.

The NPC has been known to promote the use of a “Color Plaster Waiver” agreement (between plasterers and pool owners) which states that blotchiness, streaking, and hairline cracks are normal and issues that plasterers have no control over.

Isn’t that amazing? NPC leaders are aware that excessive CC and water troweling can cause unsightly discolorations, surface cracking, and other weaknesses, yet (falsely) state that plasterers have no control over those issues, and that they are normal. Yet, when the pool owner complains of a discolored plaster surface, the plasterer often blames the service tech or pool owner for not maintaining the pool water properly – and they can use NPC literature as support.

(The above discoloration problems should not be confused with calcium scaling which is caused by out-of-balance water and usually results in a white deposit that later turns gray/brown due to dirt and minerals adhering to the scale).

Do plasterers have to use CC? No; they could use “non-calcium chloride” accelerators instead, or none at all. Do plasterers have to add excessive amounts of water to the surface and trowel that water into the surface? No, they don’t.

One has to wonder if the NPC leadership realizes that allowing inferior practices helps and benefits the poor quality plasterers by not holding them accountable. Quality plasterers know that adding CC causes problems, so they don’t use it (or very little), and make the effort and take time to finish pools properly.

Years ago, the NPC set a maximum limit of 2% CC to the weight of cement. Yet, the NPC now refuses to set any limit for CC additions and water content for white or color plaster in their new Plaster Standard. Apparently for pool plastering and discolorations; the new NPC motto is…… anything goes.

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Kudos to Service Industry News

Instead of writing a “he said, she said” article about the plaster spotting controversy, Service Industry News (SIN) thought it would better serve the pool industry by conducting their own investigation to determine what information is true, and false. They started on that goal by analyzing the Cal Poly test pool studies. In their July 31, 2015 issue, SIN presented credible evidence (from the Cal Poly Phase 2 report) that the white spotting of the plaster test pools was not caused by aggressive water.

That conclusion directly refutes the NPC’s claim that the Cal Poly study proved that white spotting is caused by aggressive water. The SIN article pointed out that when the test pool’s plaster surfaces spotted or deteriorated in balanced water, the cause obviously has to be something else.

The article contains a thorough analysis and helps readers understand the Cal Poly report and what actually happened. This was a bold and courageous move by SIN. It was also a “right” thing to do, and they seem uniquely qualified since one of their editors (Marcelle Dibrell) has a PhD in chemistry, and is capable of scientific analysis.

A second article in that issue addresses the fact that the recently written NPC Plaster Standard lacked specifications, limits, and other valuable information on very important durability issues such as; water-to-cement ratios, calcium chloride content, mixing, water troweling, and other finishing techniques.

What is baffling is that the NPC is always touting that they promote and establish quality workmanship standards. But when the NPC received requests by industry members to acknowledge that there are limits on the amount of water and calcium chloride content, the NPC reply was that since they don’t know at what level to set the limits, they won’t set any limits at all. What was the purpose of spending more than a million dollars of industry money to study pool plaster issues at Cal Poly? As the other article illustrates, Cal Poly never was about studying plaster, it was about finger-pointing.

Former NPC Chairman Alan Smith is quoted as saying that the Plaster Standard should only contain “general” specifications, and that the Plaster Standard is a living document which can be added to later. But where are the general specifications? One could say that the NPC’s Plaster Standard contains no standards. In other words…..anything goes; at least in regards to workmanship.

And is it realistic to think that the NPC will allow changes in the future if the NPC is steadfastly refusing to establish specifications and limits up front - with all of the known cement science available? Why does this industry need to wait (5 more years!) for good standards to be adopted, and why should the plasterers get away with no standards now? One has to wonder if the NPC leaders realize that allowing inferior practices helps the poor quality plasterers, while hurting the good quality plasterers.

It appears that if the plaster spotting and discoloration controversy is ever going to end, PR rhetoric needs to be confronted and corrected with the truth so that the industry is aware. Kudos to Service Industry News for doing just that.

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The NPC has drafted a plastering standard which has been submitted to ANSI for approval.  But the NPC did not include and address many proper and improper workmanship practices, such as, limiting water content (water-to-cement ratio), calcium chloride additions, and wet (water) troweling. These are all very important issues for the making of quality pool plaster.

And unfortunately, an article by Pool & Spa News about the new proposed plaster standard does not tell the whole story and misrepresents several facts.

For example, the article (incorrectly) states that “onBalance’s concerns (regarding improper plaster workmanship issues) are based on research not pertaining to immersed (pool) plaster.”  That is false.

For 15 years, onBalance has provided the industry with many studies conducted by forensic cement scientists – specifically on actual failed pool plaster that identified improper workmanship practices (including calcium chloride additions) as being the cause of certain defects and discolorations, such as white soft spotting (spot etching) and gray mottling/blotchy discolorations. (And they also determined that pool water chemistry was not involved.) The above findings are also similar to PCA and ACI findings for certain cement/concrete flatwork defects and discolorations.

The NPC’s own Cal Poly (NPIRC) study showed that adding calcium chloride in colored plaster resulted in discolored (blotchy) plaster, and that a high water/cement ratio resulted in early deterioration in balanced water.  Yet, the NPC won’t address that in their standard and won’t adopt a good water to cement ratio standard that was used at Cal Poly that resulted in good looking plaster even though the water was occasionally aggressive. Why not?

The article also says that it is onBalance that the NPC disagrees with.  No, it is the prominent cement scientists’ findings on pool plaster that the NPC has problems with and cannot refute.  And since the NPC has no science or evidence to support their self-serving positions, they make excuses and suggest that everything has already been “hotly debated,” and cannot reach a consensus. 

How does this industry reach consensus when the NPC won’t admit to those test pool results and realities, and all of the other documented plaster/cement studies?  What do they really want?

So is it okay with the industry (including some in the trade press) that the plasterers don’t set good workmanship standards that would provide a quality and durable plaster finish that will not deteriorate and discolor once submerged in water?  Is it okay that service techs and water chemistry are blamed for what are actually plaster defects and discolorations?

The NPC's proposed standard should include and be adopting good guidelines that are based on known science, and not allow poor practices that make it easier and faster to plaster pools, which can have negative effects on plaster.

It is time the pool industry is told the truth, and then we need to make this standard right for our customers.  They deserve good workmanship and a durable swimming pool plaster finish.

Here is the link to the article, and please be sure to read the comments following that article.

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Understanding Pool Water Balance

Decades ago, people in the pool industry started becoming aware that there was more to pool maintenance than just adding sanitizers to the water (to kill algae and bacteria) and filtering it (to help keep it crystal clear).  Gradually, we learned that even properly sanitized and filtered pool water could become unbalanced.


We figured out that unbalanced water could be either scale-forming, in which case a layer of calcium scale would form everywhere – or aggressive, where uniform etching (dissolution) of quality pool plaster/cement surfaces would occur.


As an industry, we needed a way to determine whether the water in our pools was potentially scale-forming or aggressive – and found it in what is known as the Langelier Saturation Index (SI).  That Index has been improved in recent years to produce better accuracy.


In his research, Langelier found that there were five key parameters involved in a body of water’s status – that is, pH, calcium hardness, alkalinity, water temperature and total dissolved solids (TDS) – and that various relationships among these factors determined whether a pool’s water would be balanced, scale-forming, or aggressive to cement surfaces.  (Note that a sanitizer residual plays no role in these calculations.)


The SI is applicable to calcium carbonate only which pool plaster contains.  Calcium hydroxide, another key plaster component (about 20%), is somewhat soluble and can be dissolved by balanced water.  (More on that issue in a future post.)


The pH value of the water is perhaps the most important factor affecting the Saturation Index (SI), with alkalinity and calcium hardness following close behind. As the pH lowers, the more aggressive water becomes, and as the pH rises, the more scale forming water potentially becomes.  The same follows for alkalinity and calcium hardness, the lower they are, the more aggressive the water becomes, and the higher they are, the more scale forming.


Water temperature follows a similar pattern:  The higher the temperature, the more scale-forming the water; the colder the water, the more aggressive it becomes.  With TDS, however, it’s just the opposite:  The higher the TDS, the more aggressive it makes the water, which makes it more of a concern in salt pools.  But TDS is a minor player overall.


The key point to master here is that all of these individual water parameters or values can be offset by the other water parameters - that’s why referring to the water’s balance is so appropriate.  A low calcium hardness of 100 parts per million, for example, would by itself tend to make the water more aggressive, but it can be offset and neutralized by a high (or higher) pH, a higher alkalinity, or a higher water temperature.  Similarly, a high calcium level can be compensated for by a slightly lower level of pH and/or (carbonate) alkalinity.


The Association of Pool & Spa Professionals set limits to the SI range:  For water to be considered balanced, the value derived using the SI should be between -0.3 to +0.5.  Let’s look at a few examples to show what that means and help us all see the sort of wiggle room that comes into play.


Let’s start with all-around “good” water values:  If the water has a pH of 7.6, alkalinity at 90 ppm, CH at 300 ppm, TDS at 1,000 ppm, a temperature of 82 degrees Fahrenheit, and a cyanurate (stabilizer) level of 50 ppm, the SI of this water will be 0.0 and is balanced.


Let’s look at what happens when the pH is on the low side, but which can be offset by a higher alkalinity and calcium level:  With a low pH at 7.2, the alkalinity at 120 ppm, the CH at 500 ppm, the TDS at 1,000 ppm, the water temperature at 82 degrees, and the cyanurate level at 30 ppm, the SI is still 0.0 and the water is in balance.


Again, look at how these figures offset one another:  If the pH is high at 7.9, it can be offset by a lower alkalinity of 60 ppm, a CH of 500 ppm, a lower water temperature of 55 degrees, the TDS at 3,000 ppm, and the cyanurate level at 30 ppm, the SI is still 0.0.


Note that there is a sixth factor in the equation:  When pool water contains cyanuric acid as a chlorine stabilizer, one-third of the cyanurate content needs to be subtracted from the total alkalinity amount before any SI calculation is made.


It also might be helpful to look at swimming pool water as dynamic and often changing.  If a pool’s water is either aggressive or scale-forming right now, it may not stay that way for very long:  When pool water has high calcium hardness and total alkalinity levels, this causes calcium to precipitate out as calcium carbonate scale, and the resulting loss of calcium carbonate from solution will cause the calcium hardness and alkalinity of the pool water to lower, thereby making the water more balanced and less likely to continue scaling.


By the same token, if aggressive water etches, dissolves and solubilizes some of the plaster surface (in the form of calcium carbonate), the calcium hardness and alkalinity of the pool water will increase – thereby edging the water toward balance – and it will stop being as aggressive as it once was.  Therefore, aggressive water can correct itself and become balanced, but also at the expense of dissolving some of the plaster surface.


However, let’s also consider that the pH in most pools rises during the hours and days after a pool has been chemically treated and adjusted by a technician on a visitation basis.  In these cases, that rise in pH will make the water less aggressive or more potentially scale-forming as time passes.  Those who maintain the pool water should take the above information into consideration for proper water balancing and understand what can occur between chemical treatments. 


The good news is that research has shown that the water can move off 0.0 in that range (cited above) of -0.3 to +0.5 without causing damage to a pool’s plaster, quartz, or pebble finish.


At onBalance, we’ve developed an SI calculator that’s available on our website.  For information, go to  The calculator is also available as a mobile-phone app.  For details, visit


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