A close look at substrate and subfloor issues

By Lew Migliore

Substrates or subfloors are the surfaces on which floorcovering materials are applied. They can be wood, concrete, plywood, stone or metal. Regardless of the material, there are specific preparation considerations that must be adhered to so that the installation of the flooring material will not be compromised. Of primary importance is the flooring material’s ability to adhere to the surface onto which it is being applied. For stretch-in installation of carpets, this is much easier, since what’s most critical is a substrate that is level, and any other factors that will affect carpet glued to the floor have virtually no bearing on a pad and tackless installation.

First and foremost, the substrate must be clean and dry. It must be free of oil, grease, parting compounds, dust, dirt, grit, chemical contaminants, sealing and curing agents, paint, drywall compound, old adhesives such as cutback, solvents, and loose or broken patching agents. The substrate must also be free of cracks wide enough to telegraph through the flooring material.

ISSUES WITH WOOD
Wood subfloors can have moisture issues, especially particleboard or OSB (oriented strand board). Wood is very absorbent and it can be dusty, so it would be necessary to apply a sealer to the surface. This can be as simple as latex milk or a sealer made by the manufacturer of whatever adhesive is going to be used or mandated (specified by the flooring manufacturer).

Wood also contains chemicals, binders or resins, especially particleboard and OSB, but plywood and luan can as well. Most adhesives contain water, which can cause a reaction with the agents in the wood, resulting in the adhesive drying out and crystallizing. This will cause loss of bond and ultimately an installation failure. Writing on wood flooring can also come through vinyl flooring as can bark chips in OSB, which will cause areas of discoloration in sheet vinyl.

Wood is treated with bug spray on occasion, which will cause anything applied to it to lose its bond. In older historic buildings once used for manufacturing, you can count on oil having impregnated the wood floors, which are waiting to attack things stuck on top of it. Furthermore, applying a cementitious agent over a wood substrate can result in the cementitious material breaking down from expansion, contraction and flexing of the wood substrate.

In apartment buildings or in smaller buildings where you’ll find this condition, you have to consider what the wood subfloor will do. The correct new wood underlayment must be used if it is to be compatible with the adhesive and the flooring material being installed. Don’t overlook the importance of the effects of wood substrates or underlayment contribution—or lack thereof—on a successful flooring installation.

CONCRETE AND MOISTURE
In the commercial arena, concrete substrates are the norm, whether new or old. One point to remember is that concrete should be considered a living material, constantly in a state of flux. Concrete is never truly dry, and is always subject to some degree of hydration. It is also full of chemicals and minerals and, if new, can contain any number of bond-breaking additives that will prevent flooring adhesives and materials from bonding to it or lead to debonding over a period of time.

Aside from any dust, dirt or contaminants that may be on concrete and that have to be removed or contained with some type of sealer, you also have to contend with the natural aspects of concrete. Concrete is a porous material through which water or other fluid materials can easily be transported, together with the water-soluble materials of the concrete itself. As such, the pore water consists of inorganic compounds and has a rather high pH, as concrete has a 12.5 pH or higher.

Coatings on concrete surfaces that are designed to dry it out or seal it can also cause an installation failure. Most of the concrete sealers will affect flooring installations. Be wary of anyone who tells you differently—they probably have a specific agenda to make you believe otherwise.

Contaminants such as oil, grease, oil-based sweeping compounds, paint, solvents and the like can create adhesion failures and discoloration of vinyl flooring materials. Writing on concrete floors with anything but a pencil, just like with wood subfloors, can assure a staining of vinyl flooring in the future, especially sheet vinyl materials, which will mirror the writing or marking on the substrate.

All of this is chemistry, and it’s important to realize that there can be reactions between chemical agents that, like it or not, will occur.

If a pre-existing vinyl asbestos flooring tile was installed with cutback adhesive—black asphalt-based material that contained asbestos—and the flooring was abated, the chemical residues, if not removed, will cause the new flooring installation to fail. If it’s a vinyl material, the chemical residues can physically distort it. This type of a failure is extraordinarily expensive to resolve. You can’t put a new leveling agent or sealer down if abatement chemicals remain, because the chemicals will come right through them.

BEST PRACTICES
There are methods to help prevent failures, whether you’re installing hard or soft surface flooring materials. You can bead-blast the concrete and seal it with several types of products, or apply a new cementitious coating or a synthetic gypsum product (which is different from regular white gypsum). Or, just apply a sealer that will actually work; latex milk is likely to be sufficient for a wood floor, but there are other types of sealers for wood specifically formulated for that purpose.

One of the most important things to remember is to make sure the substrate is clean and dry, and to use premium floor prep materials and adhesives, properly applied in the correct atmospheric conditions—often easier said than done. You might feel as though you’re expected to be a chemist and physicist to install flooring properly, but rest assured, following the directions should be enough to get the job done.