3 Dangers to Avoid When Installing Wood Floors Over Concrete

Installing hardwood, engineered, or laminate flooring over concrete sounds straightforward, but three specific problems catch installers out. Here’s what to watch for.

In situ RH testing measures moisture inside the slab.

New slabs are the usual suspect, but an old slab can cause the same problems.

Avoid These 3 Dangers When Installing Wood Flooring Over Concrete

1: Not Testing with In Situ Relative Humidity Sensors Before Installation

A new slab is the most likely to hold excess moisture, because a fair amount of water goes into mixing and placing concrete. Not all of it is meant to stay there. That excess water must evaporate through the surface before flooring goes down, or moisture problems follow.

Older slabs get there too, through a missing or damaged vapor retarder, a plumbing leak, or another external source. Whatever the source, it has to be dealt with before wood goes over it.

The way to find it is in situ relative humidity (RH) testing. Sensors are placed at 40% depth in the slab, left to equilibrate for 24 hours, and then read. Measuring inside the concrete rather than on it tells you what the surface will “see” once moisture has equilibrated under the finished floor.

2: Not Acclimating the Floor to the Installation Environment

Let flooring acclimate before installation.

Before a single board goes down, the flooring needs time to acclimate to the environment it will live in. It can’t come straight from the supplier onto the slab. Store it in an enclosed space at temperature and humidity close to the installation environment, or in that environment itself.

Wood is hygroscopic: it absorbs and releases moisture until it reaches equilibrium, expanding as it takes on moisture and contracting as it gives it off.

Install boards that are still moving and you get gaps or swelling later. Make sure the flooring has fully acclimated to the space you’re installing it in.

3: Not Using an Accurate Wood Moisture Meter

A moisture meter confirms the flooring is ready.

Acclimation is only verifiable if you measure it, which makes the meter part of the job rather than an accessory. An accurate wood moisture meter tells you when the flooring has actually reached equilibrium instead of when the calendar says it should have.

A pinless meter is the better choice on finished flooring, since it reads without leaving pin holes in boards you’re about to install.

How you use it matters as much as which one you own. Set the meter to the species you’re installing, since density affects the reading, and check boards from several different bundles rather than one convenient stack near the door. Measure the subfloor as well, and compare it to the flooring: a gap between the two tells you the flooring hasn’t finished acclimating to the space, even when the individual readings look acceptable.

What if You Don’t Test the Concrete for Moisture?

Then there’s a real chance the wood floor will cup or buckle as moisture moves up through the slab.

Testing is the easiest step to talk yourself out of, usually for one of these reasons:

• You’ve been in the industry for years
• You know the concrete you’re working with
• There hasn’t been any rain
• The building is enclosed
• The concrete looks the right color

None of those tell you the moisture reading. If you can’t look at a slab and know the number, skipping the test puts the whole job at risk.

Best Practices for Installing Hardwood Floors Over Concrete

Prep the slab first: clean it, smooth it, and test it.

Install an underlayment or subfloor so the flooring has something to attach to.

Acclimate and test the flooring. If readings come back too high, allow additional acclimation time. That extra time costs less than tearing out a floor later.

Then lay the flooring and finish the job, knowing the conditions underneath it were measured rather than assumed.

Learn more about how to install wood floors over a concrete slab the right way.

Jason Spangler

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

Last updated on September 17th, 2026