Carpet mold is nasty stuff. While mold and mildew on hard surfaces such as tile are easy to remove, getting mold out of carpet fibers and backing can be difficult or even impossible. To make matters worse, mold often appears first on the carpet backing where it is not seen until it is too late.
Conventional wisdom suggests that moisture is the primary culprit that causes mold on carpeting and that ridding the carpet of moisture will take care of the mold problem. This is only partially true, however. As a it turns out, carpet mold is surprisingly easy to keep under control, moisture-control being only half of the answer.
A Different Look at the Origin of Carpet Mold
The potential for moldy carpets prevents many homeowners from installing carpet in their basements. Basements are notoriously damp places, even those that seem dry to our sight, touch, and smell. Light humidity in the largely enclosed environment of a basement builds up over time and can cause problems for carpet and other materials. But is humidity is not the only cause of mold.
A scientific study sponsored by the Carpet and Rug Institute (CRI) has provided a more complex picture of how mold grows in carpeting and how best to avoid the problem. Studies were conducted to find out whether high humidity (such as you might find in a basement, below-grade installation) caused mold growth on carpeting.
Carpeting in various conditions (new, old, dirty, and clean) were subjected to various levels of humidity. Researchers, in particular, wanted to see if high humidity (defined as 80 percent or more) provided mold/mildew with an incubator in carpeting. What they found was that dirt, more than humidity, contributed to mold growth. Carpets that were heavily or even lightly soiled, bred far more mold than clean carpets when subjected to the same levels of moisture. Simply put, high humidity plus dirt equals mold.
Clean Carpets vs. Mold
It is worth noting that if a carpet is clean enough, it is highly resistant to mold growth despite humid conditions. In the CRI study, clean nylon carpet was subjected to high temperatures and levels of humidity (80 degrees Fahrenheit; 80 percent humidity), and no mold growth occurred. Even clean carpeting that was known to have active mold spores did not support additional mold growth.
Dirt on carpeting grows mold for two reasons. First, the dirt contains mold spores. Second, dirt itself contains moisture. The moisture in the dirt combined with the room's ambient humidity, therefore, provides a rich breeding ground for mold.
Even worse, dirt is a hygroscopic material, meaning that it readily soaks up any available moisture—whether ambient humidity or surface moisture. In other words, dirt is a moisture magnet.
How to Prevent Carpet Mold
If you have carpet in a basement or other area with potentially high humidity, there are a few simple measures you can take to prevent mold growth.
- Keep humidity low. Humidity of 65 percent or lower tends to be the perfect level for maintaining a mold-free carpet. You can lower humidity in a contained area by running a portable dehumidifier or providing airflow by leaving windows and doors open as needed (don't open the windows if outdoor humidity is high).
- Keep temperatures low. Temperatures of 80 F and higher can contribute to mold growth in carpet. Portable or central air conditioning can help with both temperature and moisture because it lowers humidity as it cools the air.
- Keep your carpet clean. While there is no official definition of "clean," it is recommended to vacuum a carpet weekly to help prevent mold growth.
- Install synthetic carpet materials. Organic carpet materials such as wool are more prone to mold growth than inorganic or synthetic carpeting such as nylon or olefin.