Sticky business

The laws of chemistry and physics drive how chemical anchors bond to concrete. When installed properly, these anchors can offer thousands of pounds of hanging or anchoring capacity.

But sometimes, the chemicals just don’t set up right or the anchor pulls from the hole once it’s put to work. Why? Because contractors act more like Red Green than Martha Stewart when it comes to installation. They start with the wrong adhesive, then follow with shoddy hole preparation and chemical mixing practices. Then they seal their fate by applying the load before the adhesive fully cures.

It doesn’t have to be this way, say chemical anchor experts. “We’ve seen tremendous improvements in chemical anchor chemistry and delivery systems in the last 10 years,” says Steve Shade, vice president of adhesive products and technical services at U.S. Anchor Corporation. “When there is a problem, it’s related to using the wrong adhesive or not following proper installation procedures.”

Duh, read the directions
Almost all anchor installation problems can be eliminated with a little reading on the front end.

“Contractors run into problems when they assume the installation procedure with one adhesive will be successful with another,” says Ray Williamson, director of engineering at Powers Fasteners.

Variations in the adhesive compounds can affect the success of the job. That’s especially important when the adhesives are of different chemistries.

Check your tool
Shade says worn, misaligned or damaged dispensing tools can affect performance. “If the unit is misaligned, or screws and nuts that hold the tool in proper alignment are loose, you will get incorrect mixing of the adhesive compounds. That can lead to reduced anchor performance.

“The dispensing tools havegotten better, but they still wear over time. We now put thread-lock on critical nuts and screws so they can’t loosen and cause misalignment. But if a tool is not maintained, it can cause the chemical to blow back inside the cartridge. When this occurs, you will not get the right mix needed and anchor performance will be greatly reduced. Solve the problem before continuing,” Shade says.

Shade says users shouldn’t try to increase dispensing speed by taking out any of the mixing elements inside the mixing nozzle. “The nozzle assures complete mixing before chemicals are dispensed into a hole. Short-circuiting that mixing will affect performance,” he says.

Test it first
Williamson recommends you do a mock installation to assure the adhesive works in the application, then show other installers how to do it correctly.

Drill the hole correctly
Williamson says the hole only needs to be slightly larger than the anchor. The directions will help you select the hole size.

“Usually, it takes a hole that is only 1/8" larger than the anchor. That’s a tremendous advantage over cementitious grouted anchors that require a hole as large as 2" for a 3/4" anchor. This results in tremendous labor savings,” Williamson says.

Blow, brush, blow
Poor hole cleaning is a common mistake. Following a blow-brush-blow sequence can assure anchoring success.

“Everyone in the industry agrees that compressed air is the way to go to clean dust out of holes,” says Williamson.

But don’t stop there, says Shade. “It only takes a second or two to brush the hole, then blow it out again before installing the adhesive and the anchor. If you blow, brush, then blow the hole again, you will guarantee the success of the chemical anchor,” Shade says.

Adhesive application
When starting with a new cartridge and mixing nozzle, Shade suggests you first run a bead of adhesive. “Run a 2" or 3" bead of material into a disposable container or onto a piece of cardboard before filling a hole with adhesive. It puts everything into balance,” he says.

Williamson suggests that in solid-base material such as concrete, fill the hole approximately halfway with adhesive, starting from the bottom or back of the anchor hole. Slowly withdraw the mixing nozzle as the hole fills to help avoid creating air pockets.

Anchor insertion
This is the easiest part of the job; just insert the anchor into the adhesive-filled hole. “Twist it clockwise until it reaches the bottom of the hole. The twisting action helps release air pockets and assures good adhesive coverage along the wall and anchor surfaces,” says Shade.

Curing time
Williamson says you must match the adhesive to the working temperature. Adhesive suppliers offer a variety of formulations for different temperature ranges.

Shade says each adhesive’s instructions have charts that show average cure times at various temperatures. “That can help you select the right product for the time of year,” he says.

Applying the load
Williamson says putting the chemical anchor under load before it fully cures is a common cause of anchor failure. “You’ll see lower performance from a chemical anchor that hasn’t quite cured,” he says.

Finally, Williamson says there’s no need to over-tighten the hanger’s fastener, especially if it’s a nut on a threaded-rod anchor.

“There is no need to bear down on the nut. This is not like an expansion anchor where greater tightening means more force is applied to the anchor walls. Applying too much torque can break the bond as the load pulls against the rod,” he says.

Published in the November/December 2001 issue of Contractor Tools and Supplies magazine.

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