I recently participated in an advisory committee meeting to discuss moisture problems in concrete. There I heard a concrete engineer say, “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. They assume the mere presence of water in the adhesive is what leads to moisture problems. This simply is not true. Unfortunately, this misperception also persists in the minds of people outside the flooring industry as well. Let me explain.
To better understand the history of adhesives, let’s go back 75 years. Installation recommendations from 1938 list two adhesives for linoleum installation: a linoleum paste and an alcohol-resin adhesive. The paste was dark gray, water-soluble, and 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.)
In 1954, the 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 cure completely (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.
Yet if today’s adhesives are as effective as ever, what has changed? Why is this still a big problem for the flooring industry?
This is easily the No. 1 issue because no matter how hard you try – and people are trying really, really hard – you can only dry concrete so fast. Attempts to accelerate the process only create headaches like cracking and curling, of which we see far too much in the flooring industry.
The Lack of Good Building Sites.Like Will Rogers said, real estate is the only thing they’re not making more of. So if the really good building sites have been taken, what must developers do? They break ground on secondary sites that present a host of problems not seen in 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 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 degrade when exposed to ultraviolet light or oxidation. The mix water should be released in about 30 to 45 days after proper application.
Although they are supposed to be applied at a thickness of one to two mils, I have seen instances where the curing compound 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 still degrade properly in the 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 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 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 Materials.
When asbestos was eliminated as a backing material, manufacturers moved to other types of fibers, some man-made and some natural that would wick moisture and not degrade. 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 unfortunately seldom match the performance.
Moisture Testing, Or Lack Thereof.
Testing a slab for moisture does not happen nearly enough. And when it is performed, it is often done incorrectly.
It wasn’t always that way. Moisture dampness testing was first recommended by Armstrong in 1941. While today’s testing procedure is much easier, it is still often not performed properly. As a result, the emphasis is shifting from this type of testing toward internal relative-humidity test probes.
As you can see, the blame-the-adhesive excuse really does a disservice to water-based products. The adhesives we use today are in most cases greatly superior to the solvent adhesives we once used. Unfortunately, due to a lack of good and/or accurate information, people outside the industry often miss that point.