Installers putting down vinyl composition tile with a latex-modifed asphalt emulsion adhesive. Photo courtesy MAPEI


Moisture problems have been plaguing our industry for the last two decades, costing up to $2 million per week. If you talk to flooring people they blame the concrete people, and if you talk to the concrete people they blame adhesives, materials and the flooring people. So who is right and who is wrong? Take a look at some of the issues below.

Adhesives: The statement I hear the most is, “The problem was caused by the water-based adhesives.” If you look at the evolution of adhesives, there were once only a few solvent-based adhesives available to the flooring industry. The first adhesives were for linoleum and were water-soluble, then came alcohol-resin adhesives, which were recommended for below-grade slabs.

Next on the scene were the vinyl products and the first of the water-based adhesives. The first multi-purpose adhesive, S-235, was invented by Dr. Carlson at Armstrong Cork Co. in 1954 and while now different in formula, it is still used today. The reality is today’s adhesives are far superior to the adhesives of the old days. The problem is getting the adhesives to cure. An adhesive can take several days to totally cure. If there is a moisture condition, it will start to appear in about 48 hours - before the adhesive gets a chance to cure. Once cured, the adhesive has a tremendous resistance to slab moisture. In a 400-day moisture study conducted about three years ago, a solvent-based adhesive for VCT finished third among the five adhesives tested.   

Materials: There have been a lot of changes to resilient sheet products, especially in the backings. The backings went from jute to rag felt to asbestos to mineral felt to vinyl backed. And with linoleum, we still have jute backing. Of all of these backings, the asbestos back products (which are no longer available) were the most resistant to moisture, because they were dimensionally stable, would not rot or decay, and worked as an excellent blotter.

There is no doubt the materials available today have less permeability than materials of old. This is due to the surface finishes on the materials which are added for ease of maintenance.

Value engineering: The “low bid, spend anything to fix it mentality” happens constantly in all phases of the construction industry. These types of contractors buy the cheap vapor retarders, lower grades of concrete and follow the path of least cost in its placement.

Vapor retarders should be a minimum of 10-mils thick, yet we see 4-mil, 6-mil, and 8-mil products used every day. Vapor retarders should be a poly-olefin rather than polyethylene. Polyethylene exposed to UV light will start to decay after 48 hours, and the decaying process does not stop after it is covered. I have observed the condition of a vapor retarder after a slab has been removed and it looked like large flakes of plastic. In some areas of the country, especially the desert Southwest, some contractors do not feel the need to use a vapor retarder. However, the arid climate is the worst area for moisture vapor issues.

Concrete mix designs: Concrete is available in a wide range of mix designs in two-grades: gap-graded and well-graded. A well-graded mix design is more costly, but helps solve some of the slab curl and cracking issues, provided it is cured properly. The flooring industry recommends a water-to-cement ratio of less than 0.50. ASTM F-710 recommends a water-to-cement of 0.40 to 0.45. Yet, the average water-to-cement ratio used for on-grade slabs is 0.58; that high of a water-to-cement ratio weakens the concrete and takes longer to dry. The ultimate reason a higher water-to-cement ratio is used is because the concrete is easier to place and finish.

Concrete curing: Curing, sealing and parting compounds need to be removed before flooring is installed. Curing and/or sealing compounds are designed to hold moisture in the slab for curing; unfortunately it also delays slab drying.

Communication gap between Division 3 & 9: The people specifying the concrete mix design (Division 3) often have no idea of what type floor covering, if any, is going to be specified (Division 9). I have seen concrete specifications for warehouse floors that were to receive moisture sensitive flooring. They failed.  

Fast track construction: This is the number one problem. In the past decade, construction schedules have been compressed 30 percent. And guess who is on the receiving end of the drying of the concrete? The fact remains you can only dry concrete so fast; once you cross that line and accelerate the drying, all kinds of problems start to occur, namely curling and cracking.

Disregard for the specifications: Flooring contractors allow themselves to be coerced into starting the job regardless of the job conditions. Remember, if you start the installation and accept the slab, it is your problem. Lighting, heating or cooling all need to be up and operational. Even more important is the slab needs to be stabilized.  Finally, and most important, the slab needs to be tested accurately for moisture.   

Moisture mitigation treatments: There are a lot of moisture mitigation treatments on the market. They are basically coatings and penetrants. Along with these products are a lot of claims about product quality and how they will work wonders. Don’t be fooled, there is a lot of snake oil out there.

Research the product that is either already down or is going to be installed. If necessary, make sure the contractors are responsible for the product they are placing. I have seen too many instances where the flooring installer gets the blame for a failed moisture treatment.

It does not matter what flooring material or what adhesive you are using; if the conditions are right you will have a successful installation. If you look at the number of installations that are completed every day successfully, there are thankfully still a lot of flooring contractors who are following the rules.