Cross posted from Howard Brickman's article on Hardwood Floors Magazine: Inspector Blog.

“Sir, we clocked you installing a wood floor on a high moisture content subfloor. May I see your documentation on moisture content of the subfloor?”

You whimper, “But officer, it looked dry to me.”

This is the wood floor guy equivalent of getting bagged with the radar gun going 50 in the 30 mph speed zone. So, how do you protect yourself? Get a radar detector. It’s called a moisture meter. Here are the step by step instructions.

-Buy a proper moisture meter.
-Use the moisture meter.
-Learn how to take the right amount of moisture tests.
-Learn how to properly use your proper moisture meter.
-Take your proper moisture meter everywhere you go.

Now let’s break it down.

– Buy a proper moisture meter: I use the Delmhorst J-4 or BD-10 electrical resistance (pin type) meters and also keep a Moisture Content Standard (also sold by Delmhorst) to check the meter for accuracy every time I use it. I am not familiar with all of the other moisture meters currently available. And Mom used to say if you can’t say something nice, then don’t say anything.

– Use the moisture meter: Check every place where there could possibly be some excessive moisture, including near exterior doors and windows, plumbing, tile wet saw, masonry and plaster mixing locations. It is not the average of the MC readings that damages flooring, it is high MC locations. Your options are to dry or replace the wet subfloor.

– Learn how to take the right amount of moisture tests. You can probably stop when you get to 50 tests in 1500’. Even on small jobs you should take at least 15 readings. Another hint: Write the date, MC, and your initials on the subfloor with a black Sharpie. Test the flooring on the bottom face and also write the test results on the pieces of flooring. If the floor has to be replaced you will have the documentation there for the world to see. It is also a great idea to record these MC readings on the work order or flooring delivery ticket or other job related paperwork that can be tucked away in the job file.

– Learn how to properly use your proper moisture meter: What does the MC number mean? Learn what “normal” MC in subflooring and flooring is for your part of the world during different times of the year by testing existing houses. Get in the habit of constantly checking your own house. Push those pins to the full ¼”/ 5/16” depth and orient the pins with the longitudinal axis of the grain (with the grain). And what does variance of the number mean? If the MC varies by more than 1% there is something changing in the building. The greater the variance, the more substantial the changes that are in progress.

– Take your proper moisture meter everywhere you go. Please…. Pretty please with sugar on it…

The best source for information on moisture meters is our friends at the Forest Products Laboratory. One of my favorites is FPL-08 Electric Moisture Meters for Wood by William James. And you can download a copy from the FPL web site.

And remember the magic words: shrink and swell.