A Flooring Contractor’s Essential Guide to Testing for Moisture on Flooring Substrates

If you are installing moisture, pH or temperature-sensitive flooring products such as hardwood, resilient flooring, rubber and even some carpet products, proper substrate moisture and pH testing along with proper acclimation is essential. Proper substrate moisture testing is not limited to concrete substrates; you should also test gypcrete and wood substrates for moisture.

Concrete

Concrete substrates should be properly tested for both moisture and pH as part of the site evaluation. I strongly encourage you to test the substrate prior to ordering the flooring since some flooring products are more moisture-sensitive than others. This will also give you an opportunity to discuss options with your customer if moisture mitigation or pH control is required.

Acceptable moisture testing methods for concrete substrates are typically ASTM F1869 calcium chloride or ASTM F2170 In-Situ RH. Please follow the flooring and adhesive manufacturer’s guidelines for maximum allowable moisture and pH levels.

You should always consider the age of the slab when moisture and pH testing concrete substrates. Elevated moisture RH or moisture vapor emissions from an older slab are an indicator of moisture intrusion. This type of moisture intrusion can indicate the required under-slab vapor retarder is missing or damaged. Broken or leaking plumbing lines can also cause substrate moisture issues.

High pH can indicate a chronic moisture issue since moisture vapor will carry salts from the concrete to the surface, raising the pH on the surface. You need to consider the grade of the slab since on- or below-grade slabs will be more prone to moisture intrusion. Below-grade slabs also have a possibility of hydrostatic pressure if the slab is below the water table at any point. It is common for hydrostatic pressure to only happen after a weather event and go dormant during periods of low precipitation. It is also not unheard of to have high moisture vapor emissions from an elevated slab. I was on a project in an older building, had 8 lbs. moisture vapor emissions on the eighth floor. The problem was limited to an area radiating about ten feet from the north wall of the building. In this case, the culprit was a poorly maintained exterior wall, which allowed moisture to enter from the side.

Gypcrete

Fortunately, gypcrete is one of the easier substrates to moisture test since you can use a pin meter that has a gypsum setting. Gypcrete must be tested per the manufacturer’s guidelines. In most cases, gypcrete substrates need to have a moisture content at or below 5% on a gypsum scale. You need to allow the gypcrete to dry prior to covering it with non-breathable floor covering. Failure to do so can cause a variety of issues including flooring failures, substrate failures and even mold developing between the subfloor and the ceiling assembly below.   

Wood

Wood substrates should be tested with a pin meter that has a wood setting. The acceptable moisture content will vary from region to region. If you are installing hardwood flooring, a general rule of thumb is the moisture content of the subfloor should be within 4% of the moisture content of the wood floor covering.

Acclimation

Acclimation should never be overlooked when you are installing resilient flooring, rubber or hardwood unless the flooring manufacturer specifically does not require acclimation. Many flooring products are sensitive to both temperature and humidity fluctuations, so having the space under HVAC control at service temperature and humidity is essential for a successful installation. Remember the flooring should be acclimated to the room it is being installed in since environmental conditions can vary in different parts of the building. The service temperature and humidity of the space is what the space will be maintained at when occupied. Some temporary heating systems can add moisture to the space creating ambient RH issues. A system like Floor Cloud will allow you to monitor temperature and humidity of the space remotely before, during, and after installation. You can use a hygrometer to monitor ambient temperature and humidity conditions on site if a system like Floor Cloud is not an option. Having an infrared thermometer to check substrate and flooring temperatures during acclimation is essential. Document all of the data collected including dates and keep the information in the project file.

Conclusion

Doing your homework with proper moisture and pH testing can save you headaches, time and money. Proper acclimation at service temperature will help you avoid flooring failures from dimensional changes. Documenting all the data collected including testing locations and keeping that information with photos in the project file is critical for your protection. Remember, every test you perform is only a snapshot in time. Those conditions can change from unforeseeable factors. Having your testing results documented is the only way to show you did your due diligence.