I had one lady who had had migraines for years, she couldn’t figure out what was going on, and this was just like accidental, it was by luck.
“So she asked me, you know, please take off your shoes when you come into my home. (‘No problem.’)
“So I get there and I’m walking around the room, I’m walking around the house checking everything out.
“I get to the master bedroom, my shoes are off.
“She’s got carpet and I just felt a little bit of dampness on the bottom of my feet, and I looked under her bed and she had slats—wood slats—on the bottom of her bed that were covered in white fuzz, all under her bed.
“Concrete tends to be somewhat porous, so there’s capillary action that can take place, and it pulls moisture up through the concrete.”
Mold Solutions CEO & Founder, Brandon Faust, February 1, 2024
“And what was happening is the slab, which is that concrete, tends to be somewhat porous. So there’s capillary action that can take place, and it pulls moisture up through the concrete and now it’s damp enough that the wood close to the concrete is moist enough that it’s this raw wood, and she had a massive colony of Aspergillus under her bed.
“And that was what was causing the issue.”
The Science Behind this Story
Concrete not only requires large amounts of water to produce, but it will forever be potentially porous, and a conduit through which the slightest amount of moisture can come through, sometimes creating a mold problem.
This is a primary reason why converting basements into living quarters (called “finished basements”), requires careful consideration and specific engineering.
When laminate flooring, carpet, wood, or any other covering are set directly on concrete, mold is very likely to occur over time, and to be very widespread, if it has not specifically been considered and accounted for.
While many of us think that concrete dries in 24 hours, that is not so on home builds: Concrete pours for new buildings require weeks or months to dry—28 days per inch of slab thickness if conditions are right.
Beyond the drying time that new concrete slabs require, unsealed concrete can forever be subject to capillary action, a condition of physics that causes water molecules to travel from wet to dry substrates or surfaces.
If you’ve ever dipped the edge of a paper towel into a glass of water and watched it soak fibers that were not submerged, you’ve seen capillary action in progress.
“If you dip a paper towel in water, you will see it ‘magically’ climb up the towel, appearing to ignore gravity. You are seeing capillary action in action, and ‘climbing up’ is about right—the water molecules climb up the towel and drag other water molecules along.”
USGS.GOV, “Capillary Action and Water,” June 5, 2018
The solution to this is a question of engineering: Finished basements and all areas of a home where almost anything fibrous, organic, and even inorganic, is set directly on concrete—carpet, laminate, tiles—are prone to mold growth if the exterior environment and the concrete itself is not properly treated and sealed.
Related References & Resources
- “Construction materials, like concrete, aggregates and sand, are porous and allows water molecules to rise due to capillary action. This creates a ring of dampness in base of buildings or structure including lateral walls due to accumulation of capillary water.” Civil Engineering Organisation, “Effects of Capillary Water on Structures and Foundation,” July 16, 2020
- “Without capillary breaks between footings and foundation walls, unhealthy conditions can develop. Capillarity can also lead to premature deterioration of materials sensitive to moisture and mold growth.” – Dörken Systems, “How to Build a Dry Basement with Membrane Capillary Breaks,” April 4, 2023
- “Exposures in damp buildings are complex. They vary from building to building and in different places within a building. Moisture allows indoor mold to multiply on building materials and surfaces.” – U.S. CDC, “Dampness and Mold in Buildings,” July 27, 2023.
- Learn what the CDC, NIH, Mayo Clinic and other reputable sources say about mold allergies.
- Story as recounted by IICRC & NORMI-Certified Mold Remediation Specialist Brandon Faust, on Feb. 1, 2024.
“Exposure to mVOCs from molds can irritate the eyes and respiratory system and has been linked to symptoms such as headaches, dizziness, fatigue, nasal irritation and nausea.”
Illinois Department of Public Health, “Mold and Your Health”
Organic Substrates and Overlays Amplify Issues Caused
“One of the ones that I’ve seen is kind of a shocking visual when you actually see it. You have like laminate flooring that gets placed over a concrete slab—as sometimes people want like sound soundproofing or they want the floor to be a little bit softer—so they put down almost like this cloth that has a plastic kind of covering where it acts as a vapor barrier.
“And when I’ve seen that, I’ve seen homes where every room had a massive colony of Chaetomium, which is a highly toxic mold.”
“Concrete is porous so it does actually have capillary action. It’s only about four to six inches, so if there’s water, if it’s not dry underneath there, it’s going to soak water up and then if you have stuff that’s going to trap that moisture.
“Especially if it is organic material and then you put wood on top of it, you’ve set up a situation where there can really be a tremendous amount of growth.”
Mold Solutions CEO & Founder, Brandon Faust, “How to Identify and Handle Mold in Your Home,” September 20, 2023
“Especially if it is organic material and then you put wood on top of it, you’ve set up a situation where there can really be a tremendous amount of growth.” – Brandon Faust, Founder of Mold Solutions.
