One of the first things we do is check the current subfloor moisture content to see if there are any issues we need to remediate before we schedule material delivery. If the job site conditions are not within normal living conditions upon our initial inspection, we will work with the person responsible for remediating to an acceptable level. Once conditions are acceptable, we deliver the material to the job site.
We then check the moisture content of the flooring on the delivery date. We see if we are within the correct parameters of subfloor moisture content versus floor moisture content. If not, we allow the flooring to either gain or lose moisture depending on job site conditions. Once we are able to see that they are within NWFA guidelines, we will install the flooring. We are not checking MC in just one or two places; we are taking numerous readings to make sure all the flooring is at the same MC. We do the same for the subfloor as well. This doesn’t take much time, but it’s essential for a successful installation. We will photograph meter readings to verify the results as well.
Moisture meters are used on every project we do. We use them from the time we first visit the project to start gathering data on the structure, all the way to the last coat of finish. Moisture testing helps us determine acclimation time, which moisture mitigation system to use, and even when to do some of our finishing/staining. But don’t just do the tests, make sure that you document the process and that everyone involved receives copies of the tests performed. If you only own one moisture meter, you will soon find that you need a few more. They all have a purpose, and their need will vary from job to job.
In short, a visual inspection of the job site, in and out, looking for signs of previous or current water damage is the first thing. Next, I would measure the RH and temp, or get that range from the owners if it’s a construction site, so I know what the EMC is. Then I take 20-40 boards, always the 1-footers I don’t use, and that becomes my moisture reading control group for the term of the job site. What happens to them, happens to the floor. Once in the EMC range, I install. I can take weekly readings of the control group on long-term jobs to see if any significant changes occur week to week. On more high-profile jobs, I also employ a data logger that can monitor and save historical information for RH/temp and MC.
The sources of moisture that can affect the way the wood will perform post-installation aren’t always detectable unless you use a moisture meter. It’s imperative that moisture meters are used correctly when assessing the moisture in a wood subfloor. First, ensure the meter is on the correct setting. Many moisture meters have a species correction for different types of subfloors, and many have a plywood setting and OSB setting. If the subfloor is solid board (ship-lap), it’s important to know the species to get the most accurate reading.
If the meter is an older model that doesn’t have a pre-set species correction built into the unit then you will have to obtain a species correction chart from the manufacturer, these are usually available online. Most moisture meters use “fir” as their default setting, and the chart lists the different species in relation to the reading the unit is receiving.
The industry standard for moisture testing is 20 readings/1000 sq. ft. for subfloor testing and 40/1000 sq. ft. of flooring material. The moisture content difference between the flooring and the subfloor should be no greater than 4 percent for flooring 3 inches and narrower and 2 percent for flooring 3 inches and wider.
It’s always a good idea to look at the most conspicuous areas when testing the subfloor. Quite often doors and windows are left open during new construction or replaced during renovations. Standing water may have been on the subfloor for a long period of time elevating the moisture content of the subfloor in these areas.