One of the most important processes in flooring projects is the testing of subfloors for moisture, in particular concrete slabs. A concrete slab is always born of moisture. In order to “pour” a slab, a dry cement must be mixed with water in order to move it and allow it to settle in a level form to develop the floor plan where the structure will sit. Depending on area of the country, current weather, and indoor climate control, and substrate condition, each slab will “cure” at a different rate and must be checked for moisture content prior to installing flooring that is susceptible to the effects of moisture. The floors that are most vulnerable are glue down hardwoods, sheet vinyl, glue down vinyl plank, VCT, and a multitude of other custom products that require adherence directly to the slab.

Types of Moisture Testing

There are two common types of moisture testing performed today that are accepted by most manufacturers as sufficient measures of slab moisture content: Calcium Chloride Tests and RH (relative humidity) Probe Tests. Calcium chloride testing has been around for decades and has generally been the most common moisture testing since it’s inception. Calcium chloride tests are easy to perform and relatively inexpensive so they are the go-to option for the DIY market and novice installers. This type of testing does require time (at least 24 hours left directly on the exposed slab) to get results, so retailers and installation companies have moved towards probe testing for efficiency and better accuracy. Performing a RH probe test requires drilling into the slab, inserting the probe, and then observing results from the coordinating digital meter. These meters are not inexpensive, therefore they lend themselves to professionals who will use them often and that rely quick results.

Preventive Measures

As with any home improvement, flooring requires preventative measures to be taken to ensure performance, longevity, and to avoid any costly future repairs/replacement. The biggest enemy with flooring is always moisture. Unexpected natural disasters such as floods, as well as in-home accidents like a dishwasher leak or toilet overflow often can’t be avoided, but subfloor moisture can…and should. What most people don’t realize is that there are factors that affect moisture content in a slab that go unnoticed. It may look dry to the naked eye, but that sprinkler system that directs water right to the base of your home may be keeping the slab “wet”. Is there a hill on your property that directs rainwater toward your home? That’s a likely culprit, too. There are multiple ways to treat your subfloor prior to installation of flooring that will protect it from underneath (which can be more dangerous than what happens on top). One option is to use a roll-on moisture barrier. These products seal the subfloor from moisture vapors escaping. If installing glue down flooring, it is important to purchase a product that will not inhibit the performance of the adhesive you have chosen to use. Some adhesives also offer moisture protection from the slab in the form of a moisture barrier/adhesive combination. These products are generally good for low-moderate moisture content in the slab and will warranty as such. If using a floating floor installation method, a simple underlayment with attached moisture barrier combination is usually sufficient for moisture protection and often adds thermal and anti-fatigue properties to the installed flooring.

Why Moisture Test?

Flooring is a major home improvement investment…in some cases the biggest one in a remodel or rehab. Taking a simple step to measure the moisture in your subfloor and then treat it accordingly prior to installation can save thousands in future repairs from preventable failure. Every manufacturer has different allowances and procedures to follow in order to keep their warranty valid. Please refer to your manufacturer warranty and installation instructions for details. As always, your certified installer will provide you with the proper advice for your particular situation.