If there is one thing every veteran installer knows it is this: moisture is our enemy. It can often take some time, but if it is not addressed adequately the presence of even a small amount of moisture can undermine an entire floor. This is why accurate testing is essential. The standards must go beyond your instincts and experience. And this is why manufacturers take pains to set minimum acceptable levels. For the installation of vinyl-backed sheet products the manufacturers have particularly tough standards. This is understandable given the nature of sheet products. They can actually trap and hold the moisture and over time that can become a huge headache. But knowing that doesn't make it any easier to achieve the moisture levels mandated by manufacturers.
In fact, the ability to reach acceptable levels of moisture is becoming more and more difficult for installers-particularly those who are under the gun to get a job done as quickly as possible. The reasons include the following:
- The actual amount of time required to sufficiently dry concrete in a fast-track world. You can only dry concrete "so-fast" before the slab starts cracking, curling and exhibits other potential problems.
- Concrete that is value-engineered or whose water-to-cement ratio (0.50 or higher) is too high to allow for a quality slab that will dry faster.
- A slab without vapor retarder/barrier or one that has an inadequate vapor retarder
- Drying time extended by curing and sealing compounds on the surface of the concrete. These compounds are designed to hold the moisture in the slab for hydration purposes.
Environmental conditions may be greatly influenced by the humidity level of the geographic region, the season of the year and the absence of humidity controls that aid drying. (The cooler the environment the slower the drying process and without temperature controls the drying time of the slab is extended.)
Issues with the substrate are often beyond the installer's control. But the environmental factors can be addressed. This is true even in areas of the country where reaching an acceptable moisture level (typically 3 pounds/1,000 square feet/24 hours) is almost impossible to achieve. That's where a moisture remediation treatment comes in. The object is not to stop the moisture movement, but to control it.
There are basically two types of moisture remediation products; penetrants and coatings. Penetrants are designed to penetrate the concrete, and interact with chemicals or compounds and create a crystallization or gel. This consolidates the concrete making it more difficult for the moisture to travel through the capillaries. A coating (either epoxy or urethane) bonds to the surface of the concrete and slows diffusion of the moisture vapor. Moisture remediation companies may use one or the other or both in their treatment of concrete slabs, depending upon the severity of the problem. In almost all cases the surface must be mechanically abraded to remove any curing or sealing compounds and/or laitance. This will open the pores of the concrete to allow for better penetration of the penetrants and/or better mechanical bonding of the epoxy-like coatings.
Once the penetrant or coating is applied the question of compatibility with the adhesive comes in to play. To assure that the compatibility and mechanical bond are just right, most moisture remediation companies rely on a cementitious or a Portland-cement based underlayment. These treatments can be applied with a hand trowel or may be self-leveling products applied over the surface. However effective the process may be there are several questions an installer must answer before he proceeds:
Is the underlayment porous or non-porous?The installer needs to determine whether the substrate is absorptive enough to handle the moisture in the adhesive. Knowing this allows you 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, sprinkle some water droplets onto the surface of the concrete and note the time it takes for the water to be absorbed into the substrate. If the droplets bead up like a raindrop on a car hood and stays that way, that means the surface is non-porous. If the droplets are absorbed and a damp spot emerges then disappears, it is considered to be porous.
How thick is the underlayment?Most installers look at a cementitious underlayment and mistakenly believe it is porous. A skim coat or any coating less than 1/8" of a cementitious material is not porous. Most manufacturers of cementitious underlayments recommend that a coat of underlayment material be at a minimum of 1/4" thick. At that point the cementitious material works 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 if the thicknesses is less than 1/4".
How is this underlayment going to affect my adhesive?All cementitious underlayment products have calcium aluminate or like chemical to work as an accelerator for hardening and drying purposes. When applied to the substrate, these water-starved chemicals will leach the moisture out of the adhesive. This also means the adhesives' working time is shortened by as much as 50 percent. As a result, working time is seriously curtailed when the installation is over a cementitious underlayment, regardless of whether it is a hand-troweled or a self-leveling application.
There are several ways to counteract this. You can use a flat-trowel coat of the adhesive as a primer or use a liquid primer (made by adhesive manufacturers) to slow absorption of the moisture from the adhesive. Or you can plan the adhesive applications with the accelerated drying time in mind by managing the size of each adhesive spreads. A word of caution: Failure to plan for the correct working time could result in bubbles if the adhesive is too wet or too dry.
If the adhesive is too wet, the moisture cannot escape and thus cannot dry. Prolonged contact to the vinyl-backing will then cause the material to expand resulting in bubbles at the weakest spot in the adhesive bond (it's also a good reason to thoroughly roll the material with the proper weighted roller). Also, when adhesive is allowed to flash too long it tends to lose its pressure sensitivity. Once this occurs the bond is compromised and a bubble will soon appear, generally after the maintenance procedure has begun.
To correct any bubbles you first need to find what caused them. This is done by looking beneath the material to monitor the condition of adhesive. If the adhesive is gummy, stringy or damp, it would mean the material placed into the adhesive was too wet or that 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 air trapped beneath the material that was dispensed during the rolling process.
Bubbles that result from 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, which can compromise the aesthetics of the floor. 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 use a needle to puncture the material on the edge of the bubble, (do notcut it with a knife point). Then, attempt to "shock" the bubble by heating it with a hot air gun that's hot to touch (remaining careful not to scorch the material), roll the spot with a steel hand roller to force out the trapped air and force the material into the adhesive, and immediately place a cold, damp white cloth (or a towel will do) on 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 not to use too much or excess adhesive will 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 like a real pro and eliminate all of the concernsbeforethey undermine your work. The biggest pitfall is walking into a jobsite and assuming the floor is a dry concrete slab ready for the installation to start.