I recently participated in an advisory committee meeting in Houston to discuss concrete moisture problems. A concrete engineer made the statement, “The problem with the flooring industry is they use water-based adhesives.” I had to object. In the eyes of the concrete and construction industry, it seems the entire flooring industry is to blame for the prevalence of water-based adhesives. The presence of water in the adhesive, they assume, is what leads to moisture problems. This simply is not true. Unfortunately, it is a misnomer that persists in the minds of people outside the flooring industry. Let me explain. 

To better understand the history of adhesives, I looked back 70 years. Installation recommendations from 1938 listed two adhesives for linoleum installation: a linoleum paste and an alcohol resin adhesive. The paste was dark gray and water soluble, and was recommended for jobs on or above grade. The alcohol resin, a yellowish-brown material made using denatured alcohol and oil-based adhesive, was recommended for below-grade installations. (Alcohol resin adhesives, when subjected to an alkaline condition, would crystallize and lose bond.)

When I started in the flooring industry, installers were still using two versions of these two adhesives; a linoleum paste and a white linoleum paste along with an alcohol resin and a white alcohol resin, known as white waterproof.

In 1954, Armstrong Cork Company patented a water-based adhesive that could be used at all grade levels. They called it Armstrong S-235 Multi Purpose Adhesive. While it has gone through numerous changes over the years, S-235 is still around today. Why? Because it works. A water-based product that has been dried and cured is very resistant to moisture—assuming you are not working with a slab that contains high moisture. If you are, the moisture vapor emissions can compromise the adhesive before it can totally cure (usually three to five days). Typically, the moisture from the slab will manifest during the first 48 hours thus preventing the adhesive from drying. So, if the floor fails it is not because of the adhesive, it is due to the conditions in which the adhesive was used. (I would also note that there is currently a water-based vinyl composition tile adhesive that will outperform asphalt “cutback” tile adhesive.)

Yet if today’s adhesives are as effective as ever, what has changed? Why is this still a big problem for the flooring industry? Here are some answers:

Fast-Track Construction.  This is easily the No. 1 issue because you can only dry concrete so fast. Attempts to accelerate the process only create headaches like cracking and curling, which we see too much of in the flooring industry.

The Lack of Good Building Sites. It has been said that real estate is the only thing they can’t make any more of. So if the really good building sites have been taken, what do developers do? They break ground on secondary sites that present a host of problems not seen with the A-list sites.

Concrete Mixed Wrong. Too often the water content of the concrete is too high. ASTM F-710 recommends a water-to-cement ratio of 0.40 to 0.45 and the flooring industry says a water/cement ratio should not exceed 0.50. Still, the average water/cement ratio in North America is 0.58. That may not sound like much, but in some geographic areas you will never be able to get the concrete slab dry enough to install a highly moisture sensitive flooring material. At the very least you will need a moisture mitigation treatment.

Curing and/or Sealing Compounds. When applied to the concrete’s surface, these products are designed to retain the mix water in the slab for curing and hydration purposes. This topical treatment is formulated to degradate when exposed to ultraviolet light or oxidation. The mix water should be released in about 30 to 45 days after the proper application. Although they are supposed to be applied at a thickness of between one or two mils, I have seen instances where the cure and/or sealer was three to four times that thickness. Does anyone think that a coating twice as thick as it is supposed to be will degradate in that allotted time? The trend is gradually evolving back to the old method of wet curing. Once wet curing is stopped the slab starts to dry.

Cheap Vapor Retarders. The construction industry is forever “value-engineering” things. Why use a plastic membrane of proper thickness that is specifically designed to serve as a vapor retarder when a thin piece of recycled plastic is available at a fraction of the cost? Worse yet, some skip the vapor retarder altogether. For those who take shortcuts here, the question is not if moisture is going to be a problem, but when.

Changes in Resilient Sheet Material. Today’s products are not as permeable as those seen in years past. That’s because manufacturers have worked to supply end users with flooring that is easier to maintain as a way to help trim maintenance costs. That’s a great selling point but it also invites more moisture issues. Unfortunately, the more permeable the surface the harder it is to maintain.

Changes in Backing Material. Once asbestos was (with good reason) eliminated as a backing material, manufacturers moved to man-made and natural material that would wick moisture and not degradate. These replacement materials are also designed to remain dimensionally stable and help prevent the growth of microbial contaminants. While they may be far superior to asbestos from a health (and legal) standpoint, these replacement materials seldom match the performance.

Moisture Testing? What Moisture Testing? Testing a slab for moisture does not happen nearly enough. When it is performed, it is often done improperly. It wasn’t always that way. Moisture dampness testing (calcium chloride) was recommended by Armstrong in 1941. While the test today is much easier it is still often done incorrectly.  As a result, the emphasis is shifting from this type of testing toward internal relativity humidity test probes.

As you can see the blame-the-adhesive excuse is really a misnomer about water-based products. The adhesives we use in the flooring industry today are almost always greatly superior to the solvent adhesives once used. Unfortunately, people outside the flooring business often miss that point.