For the installation of vinyl-backed sheet products, manufacturers recommend the moisture levels to be at 80% as required by the ASTM F2170-02 “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs using the in situ Probes.” The ability to achieve these numbers is becoming more difficult to obtain.

 

There are several factors that make these requirements difficult to reach, these are as follows:

1. Time required to sufficiently dry concrete in a fast-track world. You can only dry concrete “so-fast” before cracking, curling and other adverse things begin to happen to the slab.

2. Concrete that is value-engineered or has too high of a water-to-cement ratio (0.50 or higher) to allow for a quality slab that will dry faster.

3. A slab without vapor retarder/barrier or one that has an inadequate vapor retarder

4. The use of curing and sealing compounds on the surface of the concrete which are designed to hold the moisture in the slab for hydration purposes, extend the drying time.

5. Areas of high humidity. Seasons of the year, when the humidity is extremely high and the structure lack humidity controls that will aid the drying process.

6. Areas of cooler temperatures. The cooler the environment the slower the drying process and without temperature controls the drying time of the slab is extended.

 

There are certain areas of the country that reaching the moisture requirement of 80% is almost impossible to achieve without the use of a moisture remediation treatment. The object of a moisture remediation control system is not to stop the moisture movement, but to control the moisture.

Moisture Remediation System

There are basically two types of moisture remediation products: penetrants and coatings. The penetrant is designed to penetrate into the concrete, interact with chemicals or compounds in the concrete and to create a crystallization or gel, which consolidates the concrete making it more difficult for the moisture to travel through the capillaries in the concrete.

The other type is an epoxy or urethane coating which bonds to the surface of the concrete and slows the diffusion of the moisture vapor. Moisture remediation companies will use either penetrants, coatings or both in their treatment of a concrete slab, depending upon the severity of the moisture contents of the concrete slab.

In almost all cases the surface of the concrete needs to be mechanically abraded to remove any curing or sealing compounds, open the pores of the concrete to allow for better penetration of the penetrants and/or better mechanical bonding of the epoxy-like coatings.

 

Compatibility

Once the penetrant or coating is applied the question of compatibility with the adhesive comes to fruition. In order to obtain better compatibility and mechanical bond most moisture remediation companies place a cementitious or Portland cement-based underlayment, these treatments are either hand trowel-on or are self-leveling products applied over the surface of either the penetrant or coating.

This brings about several questions that the professional installer must have answers to.

 

Is the Underlayment Porous or Non-porous?

It is a must that the professional installer make the determination whether the substrate is going to be absorptive enough to handle the moisture in the adhesive. Knowing this allows them to determine how much open time is going to be required prior to dropping the material into the adhesive.

One of the best ways to make this determination is, with your finger tips, broadcast some water droplets onto the surface of the concrete and watch the droplets to determine the time it takes for the droplets to be absorbed into the substrate. If the droplets bead up like a rain drop on the hood of your car and remains that way the surface can be determined to be non-porous. If the water droplet turns from a droplet, to a damp spot and then disappears it is considered to be porous.

 

What is the Thickness of the Underlayment?

Most installers look at a cementitious underlayment and think it is porous, not true. Example a skim coat or any coating less than 1/8” of a cementitious material is not porous. Most manufacturers of cementitious underlayments recommend, a coat of underlayment material be at a minimum of ¼” in thickness.

At that point the cementitious material has the ability to work as a blotter wicking away any moisture that would affect the drying and curing of the adhesive.  Few, if any, of the self-leveling underlayments will adequately self-level in thicknesses less than ¼”.

 

How Will it Affect the Adhesive?

All of the cementitious underlayment products have calcium aluminates or a like chemical to work as an accelerator for hardening and drying purposes. These chemicals are water starved and will leach the moisture out of the adhesive, once they are applied to the substrate. Most adhesives’ open time is seriously curtailed when installing over a cementitious underlayment whether a hand-trowel or a self-leveling application; the adhesives working time is cut by as much as 50%.

There are several ways to counteract this effect: use a flat-trowel coat of the adhesive as a primer; use a liquid primer, made by adhesive manufacturer, to slow absorption of the moisture from the adhesive; or plan your adhesive applications in conjunction with the accelerated drying time by managing the sizes of the adhesive spreads. Failure to plan for the correct working time could result in bubbles in the material from either the adhesive being too wet or too dry.

When the adhesive is too wet the moisture cannot escape, the adhesive cannot dry, and the moisture is in contact with the sheet materials backing. Prolonged contact to the vinyl-backing will cause the material to expand resulting in bubbles occurring at the weakest spot in the adhesive bond (it’s also a good reason to thoroughly roll the material with the proper weighted roller).

When the adhesive is allowed to flash too long it tends to lose its pressure sensitivity. Once this occurs the bond is compromised and the bubble will soon appear, generally after the maintenance procedure has begun.

To correct any bubbles you would first need to determine the cause of the bubble. This would be done by looking beneath the material to see what the condition of adhesive is in. If the adhesive is gummy, stringy or damp it would be a result of the material being placed into the adhesive too wet or the substrate was not porous enough to handle the moisture in the adhesive.

If the adhesive is dry and hard with little or no transfer to the backing the material was either too dry or there was some trapped air beneath the material that was not rolled out from beneath the material, during the rolling process. Bubbles that are results of the material being placed into the adhesive too soon are difficult to correct because there is still a minor amount of moisture there.

The question is, “How do you get this adhesive dry under the material without damaging the material?” If you cut it open to dry, you have a seam to contend with and an obvious visual repair, which is aesthetically displeasing to the end user. If the adhesive is left to dry on its own it may take a long, long time.

If the bubble is a result of the adhesive being too dry, you can first puncture the material on the edge of the bubble with a needle, no cuts with a knife point, then attempt to “shock” the bubble by heating it with a hot air gun hot to touch (careful not to scorch the material), roll with a steel hand roller and immediately place a cold, white cloth or towel, dampened with water onto the bubble. Depending upon the adhesive type this can be an acceptable repair.

If the “shock” treatment does not work, you will have to re-adhere the bubble with a hypodermic syringe filled with the proper adhesive. Care must be taken because excess adhesive can show-through the finished floor.

Going over a substrate that has had a moisture remediation treatment can be tricky; however, if you have all of the facts you can approach it from a professional viewpoint and eliminate all of the concerns before they occur. The biggest pitfall is walking into a jobsite assuming the floor is a dry concrete slab and ready for the installation to start.