How to Test a Concrete Floor's Moisture Level

Mitigate moisture concerns before your concrete floors get swamped

Kristin Luna
Written by Kristin Luna
Reviewed by Matt DiBara
Updated July 26, 2022
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Photo: DigitalVision / Getty Images


Flex your DIY muscles.

Time to complete

72 hours

Time depends on which test method you use.



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What you'll need:


  • Polyethylene sheeting
  • Painter’s tape
  • Calcium chloride (optional)


  • Scissors or razor blade
  • Moisture meter (optional)
  • Dehumidifier (optional)

Moisture in a home can be highly problematic. Concrete, in particular, absorbs and releases moisture and can potentially warp any wood flooring you put down if it has an elevated humidity content. You can stay ahead of any issues by keeping tabs on your home's moisture level. Looking for a DIY way to start? Here’s how to conduct a moisture test for concrete floors.

  1. Cut Up Sheets of Plastic into Squares

    In order to test moisture emissions from concrete, you’ll need to create a plastic entrapment on the concrete that will show any beads of moisture. Measure out a square, around two feet in length, from a roll of polyethylene sheeting and carefully cut it with scissors or a razor blade, making sure not to create any tears or snags.

  2. Tape the Plastic to the Concrete

    Choose a dry area of your concrete floor and tightly tape plastic all along the edge of your square so it creates an airtight seal that will trap any moisture within. Run your fingernail along each tape edge to ensure a proper seal.

  3. Inspect the Plastic

    After 48 hours, return to your test site to inspect the plastic. If there are droplets of moisture on top of the plastic, the room is humid and generating moisture. If you peel up the plastic and find it’s damp beneath, you might have a moisture problem in your concrete. Conversely, if there aren't immediate signs of water, moisture levels in the concrete are likely at safe levels. 

  4. Dehumidify and Test Again

    If you find damp plastic, you can run a dehumidifier in the room and try the test again after a day or so to double-check your initial effort. You can also use a moisture meter for an accurate reading on levels and to measure the humidity in your home. Wagner Meters is one brand that produces these devices found at home improvement stores.

  5. Place a Dish of Calcium Chloride Beneath the Plastic (Optional)

    An alternate method to use is the calcium chloride test method. Place a dish of calcium chloride within the airtight plastic dome to get a visual of the moisture vapor emission rate that your concrete slab produces. According to the Association for Materials Protection and Performance, once you place the dish beneath the plastic, wait for 60 to 72 hours, then weigh the dish to record pounds of water emitted per 1,000 square feet.  

    This test can be effective, but it’s not foolproof as it evaluates the top half-inch of the concrete slab, where 90% of MVE occurs. If you want to measure deeper than 3/4-inch below the concrete surface, you’ll need to use a backup method to ensure that you’re getting an accurate read on the moisture condition.

DIY Concrete Moisture Test vs. Hiring a Pro

This standard test method for concrete moisture is one that anybody can DIY, though you can also purchase CaCl and RH test kits, which are alternate methods of moisture level testing. If you suspect a more serious moisture issue in your home, you’ll want to follow up with a local waterproofing contractor or mold remediation company.

Additional Questions About Moisture Testing

Does your concrete floor really need a professional moisture test?

You primarily need to be concerned about the moisture level in concrete when you're dealing with a basement or other below-ground part of your house. If you find any indication of moisture in your subterranean space, consider calling in a professional for further testing and moisture control solutions.

Why is it important to test concrete for moisture? 

Testing for moisture in old concrete is a safe way to ensure that any flooring you put down won’t warp over time—this is why you should test for moisture before installing flooring. It will also help you detect any potential mold or mildew problems.

It is also very important  to test for moisture when considering any epoxy coatings, floor paints, sealers and stains. If the concrete is holding too much moisture, these products might not work and can fail much earlier than if the floor was at the correct moisture level.

When is concrete moisture testing most necessary? 

When you’re laying hardwood flooring—or any other material that doesn’t flex well with humidity—you’ll want to check the moisture level of your subfloor before proceeding. Flooring like luxury vinyl tile and bamboo performs better than more rigid materials in environments where moisture might be present. However, thorough testing is always an excellent preventative measure to control and monitor water in your home.

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