Indoor Air Quality and Concrete Slabs

Many changes have taken place in construction technology over the last 20 years. Most notably, and to the detriment of indoor air quality, the advent of much “tighter” or energy efficient building envelopes and the increased use of concrete slab on grade construction. A related factor to these problems is fast-track construction, which seldom allows the time necessary for a concrete slab to dry enough to support a floor covering.

Problems with poor indoor air quality had been discussed as ideas for centuries. Yet only recently has our understanding of the microorganisms that live among us, become a serious topic for study. In door air quality sciences now constitute a multi-faceted world-wide discipline.

Scientists at the California department of health have reported that while fungal affects on human health are not fully understood, there is enough evidence to recommend controlling these organisms by elimination of the moisture that supports growth.

Concrete slab moisture emission provides a tremendous role in contributing the necessary humidity to sustain microorganisms within the floor system. Volatile Organic Compounds in carpet products have been documented to be well within acceptable limits for VOC emission, however, no carpet system is safe from biological growth when subjected to consistent moisture source, such as that provided by typical concrete slabs. Sick building syndrome is a term used by many people, but from the microbe’s perspective, the concrete moisture emission is a very healthy thing. Microorganisms are almost always present, and multiply very well when exposed to chronic moisture from substrate surfaces such as the concrete slab.

Stachybotrys arta, growing heavily inside the carpeting of a home in Arizona. This extremely dangerous form of toxic mold produces mycotoxins that poison and even kill human occupants.

“Not all fungi are considered bad”, according to Dr. Eckardt Johanning, “but recently there have been reports linking toxic and allergenic fungi such as Stachybotrys atra with ill health… and cases of hemorrhagic lung disease in infants.” Fungal infestation in buildings has often been linked to poor drainage systems or flood damage, yet there are several cases of fungal intrusion in buildings where the concrete slab was the only moisture source.

Concrete slabs, especially those without a proper vapor retarder, can relentlessly emit moisture through the floor covering and into the building envelope. For example, a 5000 square foot building enclosure can produce between 2 and 9 gallons of water per day, every day, delivered to the floor covering in a vapor form. Sustained humidity, not just volume, works in creating a theater for microorganism growth in floors. Finally, buildings that are not well ventilated, like schools closed up for summer, allow dew point to be reached on the slab surface from humid air. For more information about toxic effects of fungi in building environments, please contact your state health department.

A mold paradise, which was found hiding under the floor, is hosted by a rather typical degree of water found in an encounter with a concrete slab vapor emission failure.

< Back to Vapor Control