All adhesives equal

By JoeLazzaro Hardwood Flooring Product Mgr. Bostik

(2) Bond strength determines how difficult it will be to remove a piece of wood once it's cured. Typically, urethane adhesives are known for their tenacious bond. However, manufacturers are cutting back on bond strength to make products more user friendly if a repair needs to be made.

EIOR SEVERAL Years. hardwood

I-' flooring installers have slowly been switching to urethane adhesives in order to comply with the Clean Air Act banning the manufacture of l-1, I Trichloroethane.

As a result, urethane adhesives have steadily gained in popularity to become one of the top selling hardwood adhesives. Now, more than a dozen urethane adhesives are on the market, retailing from $80 to $200 per 5-gallon container.

Back when chlorinated solvent adhesives ruled the market, there wasn't much difference between any particular product. Chlorinated solvent-based adhesives were basically made of rubber, clay, tackifier and solvent, and could not be modified to suit

Direct your flooring

installer customers to the proper product., a particular job. The physical properties were very similar, so it didn't matter which solvent-based adhesive was chosen. Urethanes, though, are made of polymers that can easily be modified by a chemist, thus changing the physical properties of the adhesive according to the type of installation.

Note the following physical properties to direct your flooring installer customers to the proper product:

(l) Elongation is how much a product will stretch before it breaks. Wood expands and contracts depending on temperature and humidity swings, ultimately affecting the dimensional stability of the wood. If the adhesive is too brittle (low elongation) it will not be able to stretch with the wood and the adhesive bond will fail.

If temperature or humidity changes throughout the year are foreseen, choose a urethane with a higher elongation percentage. If humidity and temperature swings are not a factor, choose an adhesive with lower elongation and lower price.

It's also important to consider the type of wood being used-solid or engineered. Solid wood expands and contracts much more than engineered wood, so a high elongation percentage (no less than 807o) would be important. Engineered wood performs well with a lower elongation percentage.

Adhesives now offer as much as 1,000 psi of bond strength to as low as 140 psi. If the floor will never be removed, won't require repairs, or is a commercial installation intended for heavy traffic, use a urethane adhesive with a high bond strength. If you anticipate potential damage from flooding, extreme weather conditions or are working with a type of wood that often requires repair, use an adhesive with a lower bond strength.

(3) Water vapor permeability deter' mines the amount of water that is transferred from the slab, through the adhesive. into the wood. Hardwood adhesives have vapor retarding characteristics, but are not vapor retarders. Water vapor permeability is measured in grams/meter-24 hours-mmHg. When comparing adhesives, just look at the first number. If one is 4.5 x l0'' g/m and another is 9.0 x l0-' g/m. the adhesive that is 4.5 has double the moisture protection, because 4.5 is two times lower than 9.

If you have moisture-related concerns, choose an adhesive with a lower value. However, never install wood flooring if the moisture level exceeds the manufacturer's recommendations.

(4) Set time determines how quickly the product adheres to the slab. By manipulating the polymer, you can get a product that sets quicker or slower based on the environmental conditions. In low humidity, some products won't set for at least 16 hours. Others will cure in only eight hours.

Generally, with high temperatures and high humidity, urethanes cure fast; in low temperatures and low humidity, they cure slower.

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