6 Outside Sources for Concrete Moisture

Leaking Drain Pipe

Concrete, like the majority of building materials, constantly interacts with the conditions around it. Temperature, humidity, and other factors all have an impact on the internal moisture levels in concrete – even when it has been deemed “dry” or has been successfully finished with a flooring or sealant.

Problems can occur when external sources of moisture cause a rise in the internal moisture conditions of a concrete slab. Unfortunately, these problems are not always visible until they have made themselves known through a significant moisture-related problem like staining, blistering, flooring failure, mildew or more. Knowing internal relative humidity (RH) levels is crucial, particularly when it’s being affected by an external source.

Outside Sources of Concrete Moisture

  1. Leaking Water SourcesSprinkler Near House
    Sprinklers, appliances, plumbing…anywhere that water is directed through or near a slab can be a prime source of excess moisture in a concrete slab if a break or damage to the pipes occurs. Undetected leaks from these sources can cause significant moisture-related damage. If localized water intrusion combines with extreme temperature changes (i.e. seasonal variance freeze/thaw cycles, or an uncontrolled building environment), it can aggravate cracking, flaking, scaling or other cosmetic and structural flaws.
  2. Groundwater 
    In any building structure, groundwater, either because of a high water table or the natural moisture levels of the surrounding grade, can become a source of slab moisture, particularly if no vapor retarder was installed. Anywhere that the ground is in contact with the concrete can become a point of possible moisture intrusion. It’s also possible for the moisture from external sources like groundwater to migrate through the slab, causing adhesive failure, mold or mildew growth, or other moisture-related problems on the opposite slab surface.
  3. Inadequate Grade 
    Natural moisture runoff from rain, snow, sprinklers, and more can be exacerbated if the grade next to the structure slopes towards the building instead of directing that moisture away from the building. Even suspended concrete systems can be affected if moisture is able to wick up through the materials in contact with the moisture at grade level. Extra measures like zero-permeable vapor barriers, external sealants, drainage systems, sump pumps or landscaping should be considered if the grade is contributing to moisture problems.

Foundation Drain Pipe

  1. Poor Drainage
    Directly connected to ground water and grade, adequate drainage is vital to removing excess water from contact with any concrete system. If drainage is not designed to handle the levels of moisture that surround a building, it can result in pooling or overflow that will ultimately be detrimental to the concrete and the building materials in contact with it. Obviously, this is best addressed during design and construction, but sometimes settling can occur, causing the drainage system to fail.
  2. Condensation
    If the difference between the temperature of a concrete slab and its surrounding air is significant, and the temperature and moisture level of the slab are below the dew point of its surroundings, moisture will collect on the concrete surface and be slowly absorbed. If this compounds with chemical interaction with the concrete’s mix components, it can also lead to scaling or micro-cracks in the slab surface.
  3. High Ambient RH
    Even the internal conditions of a building space are really external to the slab and can become a source of extra moisture in it. When the air within a building space carries more moisture (humidity) than the level within the concrete, the slab will absorb moisture from the surrounding air until it reaches equilibrium (in this case, an RH balance) with its surroundings. If conditions in the building enclosure must operate at high humidity levels, then a water-resistant sealant or flooring finish should be applied to the concrete to minimize the moisture movement into and out of the concrete.

Internal RH

Regular moisture testing can help to pinpoint possible sources of external moisture. Surfaced-based tools like concrete moisture meters or building inspection meters can be a vital part of any concrete maintenance routine but are not capable of addressing the degree of water intrusion from external sources.

Only RH testing can provide a true picture of the internal moisture conditions of a concrete slab. If an external moisture source is suspected, RH testing can indicate the level of water intrusion by accurately measuring the internal moisture level of the slab. RH testing can also confirm when repairs have successfully corrected a water intrusion problem from an external source. Because RH testing reads from within the slab, elevated moisture levels can be identified and localized for better problem solving.

Being aware of potential external sources of concrete moisture can improve maintenance over the life of a concrete slab. RH testing can confirm what may not be visible with the casual glance.

Last updated on May 22nd, 2020


  1. Jason Spangler Nancy says:

    I purchased a condo with new Lauzon “next step” Ambiance Emira series, Hickory installed in May/2019 after a glycol leak. Floors were flat when I purchased. Approx 1 month later they cupped, gaped, and cracked. The installer came out and recorded 32.8% RH and determined dry cupping. (Lauzon requires 35% RH). My insurance rep recorded 35% and could not determine an environmental factor that caused the cupping. I should say floors are not level as well. Then, my insurance company suggested a floor inspector. To our shock, he recorded 22-25% RH!! When I asked him to look at other factors of the installation he stated that he was only there to determine dry cupping-a pre conceived conclusion!! The cupping is worse in one large room. In 4 other separate rooms (all with the same exposure and HVAC system) the cupping is too a lesser degree similar to each other with no cracking/gaping. If low RH is the culprit, wouldn’t the damage be similar throughout the unit and not worse where the glycol leak was (and, dirty room where the wet/hazardous materials were kept). I have over 2700 sq ft of damaged floors. What should I do?

    • Jason Spangler Jason Spangler says:


      Thanks for the questions. To one of your questions, yes, if the environmental conditions are consistent throughout the house, I would expect to see the dry cupping throughout. That being said, the glycol and environmental conditions together may be amplifying the problem. I am going to assume that the inspector came out at the expense of the installer based on the fact that they were only looking at the dry cupping. I would go to NWFA.org and search for a certified wood flooring inspector and pay for them out of your own pocket. This way, you are now the commissioning party. I would have them evaluate the floor, from scratch, to give an unbiased opinion of the cause of the problems. Good luck.

  2. Jason: Our home in Minnesota is two years old with a small tuck under garage to store lawn mowers and gardening equipment. It is below a four season sun room and shares one common interior wall with our home. After heavy rainfalls, water pools in the center of the concrete (not sealed) garage floor. We worry about mold entering the home since some mold is appearing around the garage door although the water seems to pool away from the door. A higher stainless steel curb was recently installed at the base of the door in hopes of solving the problem. It hasn’t worked. There are two downspouts running from the roof above the sun room over the garage. Water runs under the ground through tubing to the outside. The problem appeared last summer while work on the house was ongoing and the problem was evident at that time. One of the builders told us that the problem would probably disappear after the final grading and retaining walls were installed. That work was done late this spring and early this summer. The problem persists. Our builder seems puzzled as to how/why this is happening. The plan for the house shows there was to be drain tile but no one knows if it was ever installed. Vapor barrier? Not sure! We’d appreciate any recommendations for products or processes to resolve this problem before the snow flies! Thank you.

    • Jason Spangler Jason Spangler says:

      Thanks for the question, unfortunately, I am having a hard time visualizing the layout and drainage you are explaining. If you would like, send some pictures to my email with descriptions and I will see what I can do Jspangler@wagnermeters.com

  3. Jason Spangler Willie says:

    What could be the leading factors of lifting/peaking boards? No cupping, no delamination- concrete subfloors, below grade, engineered 9/16”, glue down. Dry when installed, acclimated wood floor per manufactures specs, adequate expansion around perimeter. Adequate adhesive transfer on subfloor and wood flooring. I’m lost?

    • Jason Spangler Jason Spangler says:


      Thanks for the details on this job. Some questions that would help to potentially identify the culprit(s)

      1) What were the air temperature and relative humidity in the house during acclimation and installation? Where these conditions different when you read them during the inspection?
      2) What was the measured moisture content of the wood prior to installation?
      3) What was the measured moisture condition of the concrete slab when you installed it?
      Hopefully, you have all of this documented because it not only helps put the pieces of the puzzle together, it can help prove that you did, in fact, install to the manufacturers guidelines.

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