Get Set

Hole preparation key to proper chemical anchor installation

As you struggled through high school chemistry, did you ever wonder how the topics at hand would ever affect your daily life?

For many of us, it’s fortunate that we only need to know how to install something instead of knowing how or why something works. That’s definitely the case with epoxy or acrylic chemical-based anchors.

These liquid-turn-solid formulas provide the locking mechanism between the threads on an anchor and the rough internal sides of a hole in concrete. Although you may not understand the chemical reaction that takes place when the two compounds combine in the mixing chamber, you must understand the importance of using the right product and installing it correctly for a strong, reliable bond.

“When the resin and hardener are mixed, a chemical reaction causes the compounds to attach to one another at the molecular level. This is called polymerization, which results in an extremely strong solid. The anchor’s performance comes from the adhesive's mechanical interlock with the inserted threaded rod or rebar and the concrete and the bonding of the adhesive with the concrete,” says, Jason Liebreich, marketing manager at Simpson Strong-Tie Anchor Systems.

Skipping or sidestepping any part of the process can lead to poor anchor performance, affecting building safety and overall project life. Experts suggest the following tips for top anchor performance.

Follow specifier directions
The first step is to make sure the chemical anchor in your hand matches the specification set out by the design engineer, says Liebreich. ”Not all adhesives are created equal, so use what the engineer specifies or submit substitutes for approval.  It is also important to use products that have an ICC (formerly ICBO) Evaluation Report. This third-party review ensures that technical data is accurate and reliable and that testing was done correctly,” says Liebreich.

Dick Gonzalez, vice president at Kelken Construction Systems, concurs. “There are many types of two-part adhesives for anchoring. They may be epoxy-, polyester-, polystyrene- or ceramic-based. The costs are much the same, but tensile strength of the cured material varies greatly between products.  The chemical must have the ability to develop the tensile strength of the steel rod installed in concrete.

“Depending on the formulation, some materials are less viscose and are more suitable for anchoring in sidewalls and overhead,” he says. Other can be poured directly in the hole for faster production.

Proper hole preparation vital
There is much more to placing a chemical anchor than drilling a hole. How it’s drilled and cleaned can greatly affect the chemical’s bonding performance.

“The most common problems with installation failures are improper drilling and preparation of the anchor hole,” says Gonzalez.

“Drilling the hole with an air rock drill works best because it creates a roughness in the hole so there is a keying action between the hole sidewall and adhesive when it cures. 

“Cleaning the hole is most important because dust will impair the keying action of the chemical with the wall of the hole. It is best to blow the hole out with compressed air. Start from the bottom up, then isolate the clean hole from the next one to be blown out so the dust does not make its way back into a cleaned hole,” Gonzalez says.

Once the hole is clean, the next challenge is to assure proper mixing and curing. It’s an important step in the anchor installation process.

Use new compounds
Age affects chemical anchor composition, says Gonzalez. “Most chemical anchor products tend to break down over time, so fresher product should be always used.

“Installers often do not store the material on the jobsite at proper temperatures. They should be stored at or below room temperature,” Gonzalez says.

When dispensing, mixing is key to product performance. “It’s imperative that epoxies get mixed well. Otherwise, the chemical reaction needed to harden the chemical won’t fully occur,” says Liebreich.

“Mixing is usually not a problem if the instructions on the cartridge are followed because most come in twin tubes with a static nozzle that mixes the compounds as they are dispensed. It’s a good idea to squeeze a small amount out of the tubes and discard the material when opening a tube to assure complete mixing in the nozzle,” he adds.

“In cold weather, epoxy cartridges should be conditioned to 65 to 80 F for easy dispensing. A tube of epoxy that has been left in an unheated storage container on a cold night will be thick and very hard to dispense through a static mixing nozzle. 

Dispensing problems are often caused by the location of the holes to be filled, which can lead to wasted product because they are hard to reach or fill. Also, workers may waste material by putting too much in the hole before inserting the anchors.

Taking on too big of a project with the wrong tools can also impair the results. “Some users try to tackle larger projects with manual dispensing tools. This takes longer and increases worker fatigue. In order to save time and effort, look at pneumatic or battery-powered dispensing tools that automatically dispense the compound,” says Liebreich.

Curing the final step
Temperature plays a major role in the time needed to cure these compounds before they can bear weight.

“Problems encountered with curing are usually temperature-related. Most two-part adhesives tend to cure faster in warmer weather and installers try to rush the cure when it is cooler,” says Gonzalez.

“The two most popular compounds used in chemical anchors are epoxies and acrylics. Chemically, the epoxies are a combination of two compounds joined by a chemical reaction, which results in a solid. Acrylics are basically one compound that, when exposed to an initiator, reacts and turns into a solid,” says Liebreich.

“The big difference is performance in cold temperatures. Acrylics will dispense and cure in cold temperatures – some down to 0 F. This allows anchors to be installed and work to continue even in the cold of winter. Acrylics also maintain a more constant viscosity in colder weather, allowing them to dispense easily without the need to warm the cartridge.

“Most epoxies typically do not cure below 40 F,” says Liebreich. “If the concrete temperature dips below that temperature, the product will stop curing and pick up again once the concrete warms up.  Sometimes we get calls from contractors who are worried that the product is taking a little longer to cure. Many times, it’s temperature-related, but it may also be related to a mixing problem.” he says.

Published in the November/December 2005 issue of Contractor Tools and Supplies magazine.

back to top