Mold Growth on Concrete - Analysis & Solutions
Concrete surfaces are typically not associated with mold growth. However, if the conditions are right, significant mold growth and staining can occur.
Causes of concrete mold growth.
Mold growth requires both available moisture and a food source.
On it’s own, concrete does not provide a sufficient food source for fungal growth. Unfortunately this is not especially helpful, because like almost anywhere in a building, dust quickly accumulates on the surface. Within this layer of dust large quantities of food sources for mold are present. Therefore, unless the concrete is kept extremely clean, mold growth can occur.
Of course, even if the concrete is covered in dust, mold will not grow without sufficient moisture. In most situations, controlling the moisture, rather than the dust, is far more desirable. This includes tackling both airborne moisture (lowering the humidity) and liquid moisture (flooding, vapor drive).
How is mold removed from concrete?
Thankfully, because of the extreme durability of concrete, removing mold growth is a relatively simple process. The same setup procedures apply (containment, HEPA filtration, etc.) however, the concrete itself does not require removal and can be easily cleaned. The removal process typically requires the use of both a fungicide and physical removal of the mold. The fungicide will deactivate and kill the mold spores, but staining and discoloration will likely remain. This is often addressed with HEPA vacuuming, scrubbing, sandblasting, etc. In large commercial settings, dry ice blasting is occasionally used to remove mold from concrete.
What steps are necessary to prevent mold growth from reoccurring on concrete?
If the problem is related to liquid moisture:
If at all possible, resolve the exterior moisture issue. This may be as simple as redirecting downspouts away from the affected area or sloping the ground away from the wall. However, completely preventing moisture intrusion into the concrete often requires extensive projects such as excavating the adjacent soil and installing waterproofing and drainage. This is quite expensive. In an unfinished basement, the cost of such a project isn’t typically worth the benefit. The concrete can be kept dry from the inside with air movement and dehumidification. However, you intend on furring out a concrete wall with a moisture problem, it must be permanently addressed. Otherwise, mold growth and rot will occur in the wall cavity.
If the problem is due to airborne moisture:
Lower the relative humidity. Concrete is a poor insulator and therefore can become quite cool during the winter months. In a poorly ventilated basement, this can cause airborne moisture to condense on the surface and cause mold growth. There are three ways to reduce the RH in the area.
- Increase the temperature. The warmer the air in the room, the lower the RH. Now remember, if the temperature of the room increases, but the temperature of the concrete wall remains the same, the problem will remain. This is due to the dramatic increase in RH that occurs in the air immediately adjacent to the cold wall. However, in a fairly mild climate, the increased temperature of the air will sufficiently increase the temperature of the wall to prevent condensation from occurring.
- Improve the ventilation. Assuming the condensation occurs during the winter months, bringing in fresh air from the outside will reduce the RH inside the building. This is because warm air can hold much more moisture than warm air. So if we bring wet cold air into the home through ventilation, and heat it up, the net level of humidity will drop. It seems counter intuitive, but this can dramatically reduce the moisture load within the basement.
- Dehumidify. This isn’t our first choice, but occasionally it is the only option. There are a couple of reasons I don’t often recommend this technique. First, dehumidification requires a significant amount of electricity. Second, while it reduces the moisture in the air, it does nothing to improve the quality of the air. Musty odors, chemical fumes, VOCs, etc. will all remain in place if dehumidification is used. Alternatively, if the ventilation is improved, both the RH and the air quality will improve.
Project Report > Mold on Concrete in Basement
- RH: 80% Temp: 56 deg F. CO2 = 545 ppm CO = 0 ppm
- 15-18 inches of standing water was present throughout basement.
- Virtually every surface (wood paneled walls, ceiling, subfloor joists, concrete etc…) was covered with mold growth.
- All appliances were submerged and required removal.
- Sump Pump was present but was not running due to the power being cut off to the home.
- No ventilation to basement has trapped humidity and has allowed mold growth to occur on all surfaces.
- Mold growth was observed behind all ceiling panels on car-decking subfloor and ceiling joists.
- Significant visible mold growth was noted on the ceiling of the bathroom.
- Bathroom had a suspended ceiling which appears to have trapped water vapor and caused condensation to form. This appears to be the source of the mold growth.
- No ventilation fan was observed in bathroom.
My basement leaked during heavy rain and a towel was left on the floor. Upon removing the towel, the floor was slimy and black. How do I clean it up?
Assuming the floor is concrete, spray the area with a Borax/water solution. Clean up the solution and any debris with paper towels.
Occasionally the mold growth will leave behind a stain, even after a vigorous cleaning. The staining is an aesthetic rather than a health issue. If this occurs, steam/pressure cleaning may be necessary.