Q: In our geographic area, we experience a lot of damage from expansive soils, so a trend has developed to install structural basement floors made of precast prestressed concrete, built several inches above the ground, so that some degree of expansion can be tolerated without excessive damage. We are also experiencing the usual mold damage. Almost everything I read about mold damage involves wood construction, so my question is, will concrete be less susceptible to the growth of mold?

A: It is my experience that concrete does not support microbial growth. Dirt and dust on the surface of concrete will support microbial growth, but simple cleaning or power washing with soap (trisodium phosphate) is usually adequate to remove surface mold from concrete. Sealing concrete makes it less susceptible to dirt deposits that adhere to its surface.

Concrete can contribute to mold growth if the concrete is cold (uninsulated). Concrete slabs or walls that are in contact with the ground during the summer are usually about 20 degrees F cooler than the air and will condense moisture out of humid air. Concrete is often somewhat porous and water, through capillary action, can rise in the concrete and, at times, reach building materials that do have nutrients such as wood. Additionally, flooring such as carpets or wood floors that are installed over concrete slabs that have not fully cured (still releasing water), may contribute to microbial growth in the flooring.

In summary, while concrete itself is reasonably inert and does not grow mold, it does play a part in microbial contamination if not properly protected and installed with care.

Thanks to Mark Goldman, who is a senior air quality scientist for Engineering and Fire Investigations (EFI), a firm that provides mold investigation and indoor air quality services nationwide. Mark can be reached at mark_goldman@efiglobal.com.

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