Does it matter what self-leveler I use underneath my moisture-resistant adhesive?
Shane Jenkins, director of technical training and development at Florence, Ala.-based Schönox HPS North America, answers:
First, let’s reiterate that using moisture control and moisture-resistant products is critical for the overall success and longevity of any wood flooring installation. Excess moisture can cause cupping and buckling, and left uncontrolled, it can often lead to adhesive failures, mold growth and overall decreased life cycle of the finished wood.
Now onto our specific question. We often see adhesives with increased moisture resistance using silane-modified or urethane technology. However, without considering the moisture tolerances of the underlying subfloor material, the system is only as good as the weakest link. Not all patching and self-leveling products are acceptable for use under moisture-resistant products, so review the manufacturer’s instructions when selecting materials. Most require moisture test results and will give a limit at or above the industry standard. The two test methods recognized are MVER (moisture vapor emission rate) per ASTM F1869 (the calcium chloride test) and RH (relative humidity) per ASTM F2170. The industry minimum standard for MVER is 3 lbs./1,000 s.f./24 hours, and for RH it is 75% RH using in situ probes.
An alternative is the use of a moisture control product such as a two-part epoxy-based moisture mitigation system. This will control the moisture at the concrete level and not rely on the underlayment or adhesive system for moisture resistance.
