Concrete Moisture Test  with a Plastic Sheeting

Concrete is moist stuff. It begins moist, as a slurry of water and aggregate, and even after it hardens, moisture remains for an incredibly long time. Not only that, basement floor concrete which has hardened is subject to moisture seeping upward. It’s vitally important to find out your concrete slab’s moisture before some activities, such as installing flooring. The definitive test is with a calcium chloride kit or a relative humidity meter. But here is a simple concrete moisture test  that gives you a general idea of the moisture in your concrete.

concrete moisture test with a plastic sheeting
concrete moisture test with a plastic sheeting

How to Test:

1. Cut clear plastic sheeting into a 24″ by 24″ square.
2. Make sure that the concrete where you intend to place the plastic is free of standing water.
3. Tape the plastic firmly to the concrete with duct or masking tape. All sides must be secured.
4. Wait 48 hours.
5. Check the plastic to see if any moisture has beaded up on the inside of the plastic.


1. This is not a definitive Concrete Moisture Test . View this as the “test before the test.”
2. No beading does not necessarily indicate that there is no moisture, as this is just a simple test.  Lack of beading means the moisture issue could be subtle and is NOT an indication of a fully functioning moisture barrier.  The presence of moisture beading underneath the plastic is a good indicator that there is a BIG moisture issue.

What You Need:

* Clear plastic sheeting at least 24″ by 24″
* Masking tape

Once you have done this simple test it is best to have the other, more expensive, more extensive, more trust worthy tests done by professional flooring installers.  In-dwelling moisture probes are the most reliable tests.  Surface probes are less accurate.  pH level testing (another form of surface testing) is also form of testing (testing for alkalinity prior to a glue down tile over suspended slab) as well as the most common (but least accurate) Calcium Chloride test.

As you can see, these are the more reliable tests which often require the work of a professional.  If you are in doubt or have questions about moisture, it is always best to consult a local flooring expert or concrete slab expert with your questions.