Adhesive Anchors

Adhesive systems tend to be the most expensive concrete anchors, but they have advantages that make them ideal for some applications. They can be spaced closer to each other and to the edge of a slab than comparable mechanical anchors, so when the foundation sub leaves out or misplaces an anchor bolt, adhesive fasteners may be the only alternative. Adhesive systems also tend to be more resilient than comparable mechanical anchors, so they perform better against impact and vibration loads. Adhesive systems are available in two forms — dispensing systems and glass capsules. Dispensing systems use a gun (similar to a caulk gun) to premix the adhesive and inject it into the hole. This system tends to be the most economical, but not the most convenient. Obviously, you have to use up an open cartridge fairly quickly, and you have to pay close attention to the "nozzle time" — how quickly the adhesive sets up in the gun nozzle. Also, non-acrylic adhesives can be tough to inject in below-freezing temperatures, not so much because the bond reaction is affected, but because the adhesive becomes so stiff. Glass capsules come in two types, spin-in (such as Hilti HVA, Powers/Rawl Chem-Stud, and Ramset/Redhead Maxim), and hammer-in (Powers/Rawl Hammer Capsule and Ramset/Redhead Impact). Spin-in systems require a specialized chuck to drive the anchor in and mix the chemicals. With a hammer-in-capsule, all you need is a small sledgehammer. The chemicals mix when you pound a rebar dowel or threaded anchor into a hole containing a capsule. Typically sold in boxes of ten, capsules have a long shelf life, so you can keep them on the truck for use when needed.

Glass capsules.The simplest, but most expensive adhesive anchors come in glass capsules. Two types are available — spin-in capsules, which require a special chuck for a hammer drill to drive in the anchor and mix the chemicals, and hammer-ins, which only require a hammer to drive in a rebar dowel or threaded anchor.

 Adhesive anchors are generally available in three formulations — epoxies, vinylesters/polyesters, and acrylics. Epoxy-based adhesives cure strong and aren’t effected by water, so they can be used in damp or water-filled holes. (Redhead’s Ceramic 6 is even recommended for use under water.) But the mixing and proportions must be exact, so you usually find true epoxies only in dispenser systems with high-quality (and more expensive) mixing guns.

Dispensing adhesives.True epoxy-based adhesives are unaffected by water, making them a good choice for damp locations, such as foundation pins in water-bearing granite.

Vinylesters and polyesters cure by a chain reaction, so they don’t need thorough mixing, which is why most of the glass capsules use this formulation. The drawback is that these adhesives shrink more than other formulations when cured. Acrylics have the fastest curing times with little shrinkage. They also perform better in cold weather (for example, Ramset/Redhead’s Epcon 7 stays workable and bonds down to 0°F). With all adhesive systems, you need to be careful to clear the hole of dust or slurry to ensure a good bond to the base material. This involves using compressed air (a squeeze bulb will work if a compressor is not available), and a wire brush to roughen the sides of the hole.

Information Resources

Between the World Wide Web and a vast network of local contractor suppliers, the answer to your specific fastening needs is out there. Literature. One of the best resources available is the Powers/Rawl Fastening Systems Design Manual. This is the concrete-fastener equivalent of USG’s Drywall Handbook or the Simpson Strong-Tie catalogs. Once you’ve plowed through this one, the performance specs in other references will make a whole lot more sense. CD-ROM. ITW Ramset/Redhead offers an interesting CD — Concrete Fastening Solutions — complete with performance data and animated installation instructions. Web. Several manufacturers, including Ankr-Tite, Ramset/Redhead, Star Fasteners, and Simpson Strong-Tie, have Web sites with product listings and performance data. More useful, however, are a few sites that offer an extensive listing of distributors by state for a wide range of concrete fasteners (as well as other construction products): Construction Net:

www.constructionnet.net Blue Book of Construction:

www.thebluebook.com Grainger:

www.grainger.com