
Adhesive Bolts  
Adhesive Bolts
Sticky Business

by Duane Raleigh
You've finally mended after decking out when your flimsy bolt failed. Your accident, made famous when the last issue of Climbing used it to exemplify careless bolting, has people jeering you from Pig Rock to Kaymoor. Eager to redeem yourself, you seek out a new crag. You find one, too. Way overhanging and just minutes from the road, "your" cliff has all the trappings of a fashionable sport crag.

Only one problem: the rock is a little soft.

"No biggie," you say, "I've got glue-ins."

But what are glue-ins? And are they safe?

As you might guess glue-in bolts are glued into the rock. And as you can surmise, not just any glue and bolt will do - use the wrong ones and you'll likely wind up on the crutches again. To determine which adhesive anchors are applicable to climbing, we set a batch of every promising type we could find and then tore them out of specially made testing blocks just as we did with mechanical bolts in part one of this article. Here's what we found.

Adhesive bolts work because the glue used with them penetrates the rock where it forms a chemical coupling. With right glue, this molecular linkage can be as strong as the rock itself, meaning that a chunk of the cliff has to break loose for the bolt to pull out. Further, the glue reinforces loosely layered or fractured rock, giving adhesive bolts a decided edge over mechanical anchors. And glue-in bolts age better, too. Mechanical bolts loosen and weaken under the stress of repeated loadings and temperature changes. But in tests conducted by the fastener company Emhart/molly, 20-year-old adhesive bolts were as strong as new. And since the glue completely seals the hole, the anchor is practically impervious to the elements.

Glue-in bolts have inherent problems, however, that will keep most climbers using them in hard and medium rock, where mechanical bolts work fine. The biggest strike against adhesive anchors is their cost: the least-expensive rig is about $6 for the bolt, glue, and hanger, and some will set you back twice that much. Even if you have limitless greenbacks, glue-in bolts are difficult and tricky to set, virtually mandate using a power drill, and take full day to cure to strength, a fact that precludes placing them on lead. Still, in soft rock, the high strength and reliability of adhesive bolts far outweigh their flaws.

(Note: the glue systems we tested are specifically designed for heavy-duty bolting. Do not experiment with the numerous two-part adhesives you can find at hardware stores - these glues appear similar to the ones in this review, but they are very different and are made for lightweight tasks, like patching broken coffee mugs, and will not sustain the loads associated with climbing.)

The Glue
Glue systems come in two styles: cartridge and capsule. Cartridge glue dispenses like toothpaste, via a caulking gun. To use this glue you drill the hole, fill it half full with glue, run a bead of glue down the bolt shaft, and then twist in the bolt.

Cartridge Glues
Like all bolt glues, cartridge glue consists of two parts: one of the actual glue, and another of a hardener. Separately, the two components will hold about as well as syrup, but mix them together and the resultant chemical reaction turns them into a powerful adhesive.

The worst cartridge glue is the Rawl Chem-Fast, which forces you to mix all of the glue at once (the smallest cartridge holds enough glue for eight, 1/2 inch bolts). Activated glue hardens in mere minutes, so unless you can set bolts at lightning speed, you're bound to waste more Chem-fast than you'll use.

Hilti C-100 and Ramset/Red Head Epcon Ceramic 6 cartridge glues are more practical. These systems use special dispensing nozzles that let the glue mix outside the cartridge as you need it, so there's far less waste.

Used in conjunction with Hilti 1/2-inch by 5-inch all-thread rods in medium and hard rock, both glues are stronger than any bolt hanger. Ceramic 6 claims a higher pull-out strength than C-100 but in our tests in soft, 1000 psi concrete both glues failed around 4000 pounds in pull-out when the rock "gave" way.

Disadvantages to C-100 and Ceramic 6 include the special caulking guns required, and the fact that you're sure to cover yourself and your gear with glue, which invariably dribbles out of the dispenser. And you're still bound to lose several bolts' worth of glue and ruin a couple of nozzles with every tube, as some glue will always harden in the nozzle before you can inject it into the hole. (You can cut your losses by pre-drilling all your holes and getting an efficient installation system down.)

Do not administer C-100 in damp rock - some of the glue will bond to the water molecules instead of the rock, reducing the anchor's holding power. Conversely, Ceramic 6 and the capsule glues (discussed later) are, according to the manufacturers, scarcely affected by moisture. If you've ever snapped off a hold climbing on damp limestone or sandstone, however, you know these rocks weaken when they get wet, which also reduces the holding power of any bolt.

The Ceramic 6 and C-100 glues cost roughly the same: around $2 for glue enough for a 1/2-inch bolt. We liked the C-100 because we couldn't stand the putrid smell of the Ceramic 6, which stays on your hands for days. In favor of Ceramic 6, Ramset/Red Head says their product has a longer shelf life than C-100 and sticks to dusty holes better, so you're less likely to get a bad placement. Both glues have their pros and cons, but the caulking guns cinched our choice. The cheesy plastic one from Ramset/ Red Head gummed up, cracked, and then quit working after only 6 bolts. The sturdy metal gun from Hilti never broke down, although it too can gum up with leaked glue, necessitating a good cleaning.

Capsule Glues
Like the cartridge glues, capsule systems use a two-part glue which activates when you mix the components. Unlike cartridge glues, though, capsules encase the glue and hardener in a single glass vial, which you insert into the bolt hole, suppository style. (On overhanging walls wrap a small piece of cloth tape around the end of the capsule to prevent it form falling out of the hole.) Shoving the bolt in the hole and then spinning it breaks the vial and mixes the two glue components.

For climbing, we found that the capsule glues we tested - the Hilti HEA and the Rawl Chem-Stud - have several advantages over the cartridge glues. Primarily, they make stronger anchors. Also, the glue for each bolt is self-contained, so there's zero waste, no dispenser to mess with, and you can drill and set the bolts at your leisure.

The disadvantages to capsule glues is that you're supposed to spin the bolt with a power drill to insure a glue and hardener mix. With threaded rods this isn't a big deal as you can buy a special chuck attachment that converts your Hilti or Bosch into a setting tool. You can't, however, set eyebolts, like the Petzl Ring, with a power drill. You have to instead hammer an eyebolt into the capsule and then manually turn the bolt (spin it about 25 times) to mix the glues - a practice both Hilti and Bosch warn against. Indeed, capsule-glue hand-set ring bolts did prove weaker in our tests than threaded rods spun with a power drill. The threaded rods we tested, however, were about twice as long as the eyebolts, and this fact certainly contributes to the difference in strength.

The Bolts
You have two choices of bolts for adhesive anchors: threaded rod and eyebolts. For soft rock, which is likely the only place you'll ever use glue-ins, threaded rods are stronger because their extra length gives them more contact area. In medium and hard rock either bolt will suffice, making the cost per anchor the deciding factor for most climbers.

Threaded Rod
You can get threaded rod made for use with glue in 1/2-inch and 3/8-inch stock from Hilti, Rawl, and Ramset/Red Head. The rod usually comes in 5 1/2-inch lengths, but it can be longer. If rod is longer than your drill bit you'll need to cut it down so it doesn't stick too far out of the rock. So you don't bugger the threads that the nut goes on, trim the excess length off the end of the rod that will go into the hole. If you are using capsule glue be sure you regrind the end to a sharp point so it can slice through the glass vial with minimal resistance, insuring a thorough glue mix.

Do not use a 3/8-inch threaded rod in soft rock - the small bolt diameter doesn't supply a large enough bonding area between the glue and the rock. (In hard rock 3/8-inch Rawl Bolts and Hilti HSL bolts are stronger and less expensive than 3/8-inch glue-ins, which also suffer from work fatigue due to their external threads.) If the rock is the least bit questionable, 1/2-inch threaded rod (which requires a 9/16-inch hole) is your best bet.

You can get 1/2-inch rod in three materials: regular carbon steel, high-strength steel, or stainless steel. In dry climates, carbon steel rods or high-strength steel rods work fine. Stainless-steel rods are suitable for corrosive environments, like sea cliffs and swampy or industrialized (acid rain) areas, but are more expensive.

The only bolt hanger that works with 1/2-inch threaded rod is the Petzl Coeur P38150. Other hangers, like the Metolius SS. and the Petzl P34050, can be drilled out to fit 1/2-inch rod, but this is a laborious process that can potentially ruin the hanger.

These let you thread the rope directly through them so you can retreat without leaving slings and carabiners behind. That feature alone makes them worthwhile, especially at belay/rappel stations. Another advantage of eyebolts is that since they are made from one piece of steel, they aren't susceptible to galvanic corrosion as are threaded rods and hangers.

The stainless-steel Petzl Collinox and the zinc-plated Ring are the only climbing-specific eyebolts we tested. DMM and Trango have similar products, but these were unavailable for inclusion in this review.

The Petzl eyebolts we tested are too short to trust in soft rock - they have a 2 1/2-inch-long shaft (most 1/2-inch threaded rods have a 5-inch-long shaft). In medium and hard rock - where you're unlikely to use them - both Petzl glue-ins are bomber, although you still have to be very careful when you place them, as their short length allows little room for placement error.

The Collinox's less obtrusive appearance gives it points over the unsightly Ring. Strength wise you will never break either bolt, and their pull out capacity depends on the glue you use. In out tests the Collinox and the Ring pulled out of soft rock at about half the load of a 1/2 inch threaded rod when all the anchors were set with capsule glue, which is what Petzl recommends.

The Petzl Ring and the Collinox are metric, but you can use cheaper, easier-to-find standard drill bits rather than metric ones. Petzl suggests substituting a 15/32-inch bit for the 12mm one needed for the Collinox, and a 11/16-inch bit for the Ring's 16mm one. (Note: glue-in bolts are the only ones you can substitute standard for metric bit with - you must use the manufacturer's specified metric bit with a metric mechanical bolt.)

As an alternative to the Petzl ring anchors you can round up your own threaded, forged eyebolts from a bolt-specialty store. The industrial eyebolts we tested were 1/2 by 3 1/4 inches. The bolts we purchased were galvanized, but they are also available in stainless steel for about twice the price. These eyebolts, also tested with capsule glue, held a little more than the Petzl ones in soft rock, but because they are also short, they still weren't as strong in pull-out as the longer threaded rods.

If you use industrial eyebolts be careful to get forged, not the much weaker cast eyebolts, and check the manufacturers listed strength, which, by convention, is usually only about 25 percent of the actual breaking strength. Out eyebolts listed a 2500-pound working load, which, in theory, means 10,000 pounds ultimate strength. To be safe, get eyebolts at least this strong. Don't get welded or unwelded eyebolts either. You never know how good the weld is - and the unwelded ones can straighten under body weight. Only use the forged eyebolts with threads extending at least halfway up the shaft; smother shanks won't let the glue stick to them.

Half-inch forged eyebolts require a 9/16-inch diameter hole. To let the eye recess slightly into the rock, drill two vertically aligned grooves on the outside of the hole.

Reprinted from Climbing Magazine.