One of the current hot topics in the industry is the seeming incompatibility between concrete curing and sealing compounds and new generation, water-based resilient flooring adhesives. Over the past few years, reports of resilient flooring delamination have increased. This issue is more than just problematic; it has also become expensive. Each side is trying to push the expense of new floor preparation onto the other trade. Now, with each side squaring off, it would seem to be a proper time to analyze the problem and offer some suggestions.

The Background
It is widely believed that the origin of this conflict coincides with the 1999 issuance of the national VOC (Volatile Organic Compounds) regulations by the EPA. These nationwide directives required that the solvent content (VOC) of many architectural building products, curing compounds and resilient flooring adhesives included, be reduced significantly. (See related article on VOC in Concrete News, September 2000). In order to meet the requirements of these regulations, many of the solvent-containing curing compounds, as well as flooring adhesives, underwent mandated formulation changes, with many companies developing low solvent or water-based products.

Most concrete chemical manufacturers had high solids (typically 30%), solvent-based products on the shelf that already complied with these new solvent reduced regulations. However, as part of the new EPA/VOC guidelines, it was necessary that all low solids, solvent-based curing and sealing compounds be reformulated to a higher non-volatile solids level minimum of 25%, referencing the relatively new, ASTM C 1315, "Standard Specification for Liquid Membrane-forming Compounds having special properties for Curing and Sealing Concrete."

Common thinking
When reports of bond failures of resilient flooring and carpeting adhesives began to increase, the common thinking was that we were experiencing an adhesion failure and that the cause was the reduction or complete removal of the solvent component from VOC compliant flooring adhesives. With less solvent the adhesive was believed to no longer have the solvency power to melt into the cure/sealer film. This line of thought would seem reasonable in that hardened thermoplastic polymer resins used in curing and sealing compounds will re-melt when brought in contact with aromatic solvent, while remaining well bonded to the concrete floor. Once the solvent evaporates, the cure/sealer film will harden and reform again, this time with the adhesive firmly attached.

However, after some investigation, the thought process has gone to analyzing the difference between adhesion and cohesion failures. For the sake of review, an adhesion failure occurs when the adhesive cannot stick to a sound surface with the failure occurring at the bond plane. Cohesion failure occurs when the adhesive adheres properly to a surface, but a failure occurs within the glue mass itself. In other words, the adhesive pulls apart.

It is widely believed that many water-based adhesives do not have the cohesive power once possessed by their solvent-based predecessors. Cohesive failure further confirms that the cure/sealer is providing a bondable surface for the adhesive, and that the failure is typically occurring within the glue phase of the bonding system. Therefore, with this information it is our belief that the cause of the failure will be found in the adhesive.

What's changed?
The position that the problem lies with the low solvent adhesives is supported by reports from some cure / sealer manufacturers that the high solids, solvent-based cure/sealers, ones that have been used successfully for decades with the older solvent based adhesives, are now having difficulties with the low solvent / water based adhesives.

We submit that the concrete has not changed, and neither have the basic formulas of curing and sealing compounds. What has changed significantly is the adhesive formula itself and this is where the problem lies.

What contractors and specifying professionals need to know about it?
While the debate goes on, there are some practical things that the specifier and contractor must be aware of that may affect the cost of the project. One of the requirements of ASTM C 1315 is that there be a positive bond between adhesives and the curing/sealing membrane. The more commonly referenced curing specification, ASTM C 309, does not have this requirement. Some curing compounds meeting ASTM C 309 contain waxes and other incompatible resins, and while meeting the curing requirement of ASTM C 309, they will prove to be problematic when used with flooring adhesives.

It should be noted that curing compounds that meet ASTM C 1315 also meet ASTM C 309, but not vice versa. Caution should be exercised when applying a curing compound that meets only ASTM C 309 over concrete that is to receive resilient flooring. Only thermoplastic curing compounds should be specified or used. Choosing a material that complies with ASTM C 1315 will eliminate the guesswork.

The contractor should also be aware of projects which reference CRI 104 of The Carpet and Rug Institute. CRI 104 requires that all coatings, curing membranes and contaminants be removed from the concrete surface prior to application of adhesives. It also requires a moisture emission rate of less than 3 lbs/1000 square feet/24 hours. This is very low. Complying with these requirements, in most cases, will add additional costs to the project.

Furthermore, most water-based adhesives are very sensitive to high pH surfaces. Many adhesives now require a nearly neutral concrete surface (pH range from 5-9) to bond to. The problem is that all concretes are naturally highly alkaline (pH range from 11-13). The potential compatibility problem is readily apparent.

Many costly procedures are currently being recommended by the flooring industry to correct the conditions mentioned above. We question the wisdom of some of them. We have heard of instances where a concrete surface was required to be stripped of all curing and sealing compounds, and was then treated with an diluted acid wash, all in an attempt to lower the pH of the concrete floor surface to a level that would be more compatible with the adhesive. It is the obvious fear of adhesive manufacturers that all curing compounds, including high solids curing and sealing compounds, may interfere with their products' ability to perform. Nothing could be further from the truth.

Rather than develop adhesives that perform under normal job site conditions with normal products, they choose to exclude all options, including ones that may help their case. We submit that the pH neutral nature of polymer curing and sealing compounds can go a long way in solving the apparent incompatibility between bonding adhesives and an untreated concrete surface.

The mysterious gum-shoe case
You're walking down the street minding your own business and suddenly out of nowhere, a glob of Juicy-Fruit jumps out to block you. Since you have no intentions of changing direction ('cuz that's the kind of guy you are) you can only hope for one of two things.
  1. Adhesive Failure: The gum won't stick to your shoe. It's not part of the shoe and has no intentions of messing with, commingling with, making friends with or ever becoming attached to this foreign object.
  2. Cohesive Failure: The gum, panicked at the very thought of attaching itself decides to split. Part of the gum stays with the pavement, part with your shoe, headed for places unknown. This gum isn't as tough as it thought it was and now, battered and broken says goodbye to its other half.

1: Adhesive failure:
Won't stick to other stuff

1: Cohesive failure:
Won't stick to itself
One concrete, two very different objectives:
The objectives and concerns of the flooring industry are best stated as found in a position statement coming from one of their largest manufacturers. Curing compounds are "applied to retard the escape of water during the curing process. After the concrete is cured, the contractor needs to ensure that it dries properly.

"The elimination of free water is essential for the formation of bond between the adhesives, the flooring materials and the concrete. In the presence of free water, water based adhesives will not set up and solvent-based adhesives will not adhere. In the case of adhesives already bonded to the concrete, the water based adhesive will be displaced by water if the availability of water is sustained." If I may restate, moisture in concrete is problematic for adhesives.

The objectives of curing and sealing compounds are very clear-to hold as much moisture in concrete for as long as possible (See related article on curing by Ken Hover in this issue of Concrete News). Concrete will continue to gain strength and increase in durability as long as moisture and unhydrated cement are present. We in the cure/sealer industry, with some pride I might add, accept being guilty as charged.

What's needed now:
We support the increasing use of ASTM C 1315. We feel it is needed in the industry in that it provides the highest level of curing performance from a curing compound. Where we differ is that ASTM C 1315 should not be used by the resilient flooring industry to escape responsibility of product bonding failures that are the result of their inadequate adhesive product development. It is a little known fact that there is no one standard adhesive to determine a cure / sealers performance when under test in ASTM C 1315. A cure / sealer may pass with one adhesive and not with another. While the cure / sealer is being held to a standard, the adhesive is not.

In this matter there are clear areas of responsibility. It is the responsibility of the manufacturers of curing and sealing compounds to produce products that adequately and appropriately do just that, cure and seal the concrete. Conversely, it is the responsibility of the flooring industry to produce resilient flooring adhesives that are compatible. Some suggest that there should be an ASTM specification for adhesives used with cure/sealers for concrete. We agree, but NOT in the curing and sealing specification. The rationale for this line of thinking is that ASTM does not require concrete to meet the compatibility requirements set by the adhesive industry. Neither should this be required of cure/sealers. This debate should be held on the adhesives side of the aisle and that is where the specification should be written.

In the meantime, until a solution is found the specifying design professional and the installing contractor should be aware of these hard to fit pieces of the construction puzzle... and that it may be a costly process. It is our opinion that the cost for preparation of a structurally sound surface for a subsequent treatment should be borne by the trade that is applying that subsequent treatment. It should be the flooring contractor who should bear the cost and required liability for preparing the floor for his product. But the larger responsibility lies on the shoulders of the adhesives manufacturers, and that is to develop more user-friendly formulations of their products, ones that are not as sensitive to moisture and concrete surface alkalinity and are compatible with curing and sealing compounds. If they're smart they'll work with us, not against us.

L&M manufactures many types of curing and sealing compounds complying with ASTM C 1315. They include our popular DRESS & SEAL, and our non-yellowing, high gloss LUMISEAL PLUS. For more information regarding ASTM C 1315 compliant products visit our website at or contact your local L&M representative.

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© 2002 L&M Construction Chemicals, Inc. | ConcreteNews Summer 2002.

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