Cosmetic Appeal of Poured Concrete Hides Serious Crawl Space Hazard

At first glance, pumping concrete into a crawl space may seem logical to homeowners. After all, concrete slabs work well in the garage and basement, and it creates a nice finished look. But sealing and insulation experts say – look again. The cosmetic slab of concrete pumped into a crawl space after new home construction is different than for a basement poured during construction. It is actually worsening the indoor air quality problems it was meant to fix. The result may be the onset of “sick” house syndrome.

The number one reason a homeowner seals a crawl space is simple: it is a wet, musty breeding ground for mold. If left unchecked, mold will migrate upward into a home’s living space and create a costly health hazard. Nasal and sinus congestion, coughing, wheezing, sore throat, headaches, fatigue and eye irritation are among the common symptoms.
“Indoor air quality is something you can’t take lightly. There are over 16 million people in the United States who suffer from asthma alone. About 7 million of them are children,” says Tim Wilkerson, a crawl space expert and building science consultant.

The fact is, choosing wet, porous concrete to seal a crawl space is like hiring a wolf to guard the chicken coop. Why? A typical mix contains over 350 lbs. of water per cubic yard of concrete. A homeowner who agrees to have concrete pumped into a crawl space is unknowingly saturating the entire area with mold-friendly moisture. And don’t think the environment improves after the concrete dries. In a spacious basement, it is easy for finishers to hard trowel, or close, the concrete surface. Crawl spaces are too small and tight for that technique, so finishers merely top off the poured mass with a hand float. As a result, the slab dries with a chalky finish that disperses dust into the air when scraped by boxes or contractors – or children at play.

Unfortunately, the dust contains silica which can cause serious lung damage. So much for the “finished” look. Installing a vapor barrier – an absolute necessity – before pumping concrete also creates problems. Since the barrier prevents concrete water from seeping into the soil beneath the house, it can only escape upward. That is a lot of moisture when you consider that the concrete required for a 1,000 square foot crawl space with a 4-inch slab contains more than 500 gallons of water (which will be entrapped within the floors and walls of the home).

“I realized pumping concrete into the crawl space was actually a disservice to the homeowner. Cosmetically it may look great, but we all need to take a closer look.”
-Tim Wilkerson

Also, since concrete does not provide a thermal break, a temperature difference between the air and the concrete surface will cause condensation. And that leads to more mold.

Wilkerson knows the downside of pumping concrete. For years he too thought it was an acceptable solution for crawl space remediation. But when he discovered the moisture problems, he began experimenting with everything from water reducers to light weight concrete with the hope of developing a drier mix.

Although he succeeded in lowering the 350 lbs. per cubic yard requirement to 300 lbs., moisture and mold problems continued to persist.

“I realized pumping concrete into the crawl space was actually a disservice to the homeowner. Cosmetically it may look great, but we all need to take a closer look. A little education can save lives,” says Wilkerson.