Beginning a wood floor installation over urethane-primed concrete.
In the beginning, the dominant adhesives were the solvent-rubbers. They were the mechanic’s choice for installing vinyl asbestos tile; ceramic tile; wood flooring; and rubber- and foam-backed carpet. Indeed, solvent-rubber adhesives had great characteristics: non-freezing; rapid set-up in both cold and humid conditions; better wetting-out when concrete slabs were dusty; inherent resistance to moisture and alkali; and they did not cause wood flooring to swell and cup, unlike many of their water-containing counterparts.

Of course, there were some disadvantages to solvent-rubber adhesives as well. Flammability (many a wood-flooring job went up in smoke), inhalation of harmful vapors, and cleanup difficulty, due to the additional (and costly) solvents necessary, all detracted from the benefits of using solvent-rubber adhesives. Additionally, a specific solvent in the adhesives used in the wood flooring industry was declared harmful to the ozone layer and banned by the Environmental Protection Agency.

Moisture test after priming

Latex Moves In

As research and technology advanced, latex-based adhesives started to become more prevalent in the industry. With costs playing an important role in development, styrene butadiene rubber latexes, or SBRs, became the kings of the hill. For a long period of time, SBRs were the leader in ceramic mastics.

Acrylic latex adhesives first started advancing in popularity when they began to be developed for ceramic mastics. The primary benefits were the adhesive’s white coloration and superior shear strengths. The acrylics exceeded the ANSI requirement by 2-3 times, while the white coloration aided grout color maintenance.

Acrylics began replacing the alcohol-resin adhesives that were used for cove base installation. Alcohol-resins required solvent removers in order to clean them up effectively, and these presented a real problem when some inadvertently found its way onto the carpet. The latex adhesives could be removed using water.

The acrylics continued to expand their position in the marketplace, especially during the era of asbestos removal from sheet vinyl, with the newer vinyls becoming more susceptible to discoloration. Nearly all the existing SBRs in the marketplace had the potential to noticeably discolor certain grades of sheet vinyl, creating a light-brown coloration in the embossed areas of the sheet goods.

Next Up: Urethanes

Urethane adhesives come in both one- and two-part solutions. One of the features that make urethane adhesives so popular for glue-down wood floor installations is the absence, or low content, of water. Water in the adhesive can cause expansion and cupping in a wood floor installation. The EPA-banning of ozone-depleting solvents has helped promote urethanes to a level far beyond existing water-based adhesives, even though the cost of urethane adhesives is higher.

Urethanes add another dimension to the installation in that they have vapor-retardant characteristics that can help alleviate problems created by water-vapor transmission through concrete slabs. There have been instances, especially in the large residential sector, where urethanes are first skim-coated over the slab prior to installing more moisture-sensitive wood species.

To date, the most common complaint associated with urethane adhesives is the extreme difficulty that installers experience in replacing individual pieces of wood. The high bond strength of urethane adhesives makes the replacement process both time- and patience-consuming.

The vapor-resistant characteristics of urethane adhesives are of great interest to the carpet industry as a possible means to reduce mold/mildew/odor complaints. There are urethane carpet adhesives already on the market. Research in urethanes, by both the adhesive industry and flooring manufacturers, has accelerated recently, as the basic cost of urethane adhesive production continues to decline.