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Adhesive Anchors  
 
Adhesive-anchor setting recommendations

by Duane Raleigh
 

No matter which glue-in system you use you need to follow strict placement recommendations to insure a strong glue-to-rock bond.

1. Drill the hole to the dimensions specified by the manufacturer. (With glue-in bolts you always drill the hole larger than the bolt rod.) If you drill the hole too small or too large you'll wind up with either too little or too much glue in the hole. In either case, the anchor is weakened.

2. Clean the hole thoroughly. Glue bonds with whatever it contacts first. If this is dust or water, than you are in trouble. Blow the hole out first with a blow tube, and then scour the hole with nylon brush made for this use. Don't use a wire brush, which will polish the inside of the hole (glue doesn't stick to smooth surfaces as well). Finally, blow the hole out again with the blow tube; if dust keeps coming out, keep cleaning.

3. When using cartridge glue fill the hole about half full, run a bead of glue down the rod, and then hand twist the rod into the hole. Some glue should flow out of the hole as the rod goes in - if it doesn't you don't have enough glue in the hole and will have to pull the rod out and squirt in more.

4. With capsule glue make sure you set the threaded rod with a power drill set in the hammer mode. You can't twist threaded rod by hand and pushing the rod in manually won't properly mix the glue and the hardener. Hammer eyebolts into the capsule and then spin the bolt at least 25 times by hand - a cursory twist or two isn't nearly enough to mix the glue components.

5. Once you activate the glue, place the anchor as quickly as possible and then leave it alone. Don't jiggle the anchor during the first eight hours of drying - disturbing the anchor during this time will break the glue bond

6. Let the glue dry for at least 24 hours before loading the anchor. In our tests, bolts cured overnight were twice as strong as those that we let dry for only eight hours.

7. Glue, especially capsules, has a short shelf life. Check the expiration date of any glue before using it, and don't use a capsule if the glue inside doesn't flow.

8. Use the threaded rod supplied by the manufacturer for the glue system you're using - similar-looking rod from the hardware store is much weaker. It's especially important that you don't use blunt-ended cartridge rods to mix glue capsules, which must be mixed with a pointed or chisel-end rod. (It's OK, however, to use the pointed capsule rods with cartridge glue.)

9. Align eyebolts so the eye sets vertically. Placing the eye horizontally increases your chances of accidentally coming unclipped, and lowers the bolts shear strength.

Gluing mechanical bolts
We recommended in part one of this article that you not use externally threaded sleeve bolts. Still, the Hilti 1/2-inch Sleeve Anchor (you can't use the HSL and Rawl Bolt with glue, as it will clog their threads) used in conjunction with the Hilti C-100 adhesive, is a popular bolt at several soft rhyolite climbing areas in New Mexico.

To test this set-up we placed five, 1/2-inch Hilti Sleeve Anchors in our softest concrete block, then set an equal number in the same block but filled the bolt hole half full with C-100. One day later, after the glue had time to cure, we pulled all 10 bolts to failure and found the glued-in bolts had pull-out strengths of about 3000 pounds compared to the non glued bolts' 1800 pounds.

Although this jury-rigged system sounds strong, you are still better off using a real glue-in bolt, which is over twice as strong as a glued-in Hilti Sleeve Anchor. Furthermore, if you let the glue harden slightly (this can happen in a matter of minutes) or gum up the bolt threads with the glue, then the expansion sleeve won't spread, and you'll have an anchor that is weaker than if you never used glue in the first place.

If you insist on employing this risky method, make sure you use Hilti C-100 glue (other glues don't stick to the bolt as well), and the Hilti 1/2-inch Sleeve Anchor, which is the only one we found with large enough cut outs in the sleeve to let the glue bond to the inside of the bolt. (Again, don't use glue with the Rawl Bolt, or the Hilti HSL, or with any other non-glue-in bolt including the wedge bolts - the glue will prevent these anchors from expanding, and will cause them to fail at below-normal loads.)

Reprinted from Climbing Magazine.