No wonder you're looking at this title twice. Mold on concrete is something you probably don't expect to see. But there it is, on a concrete floor, wall, patio or walkway. Concrete itself does not promote the growth of fungi; it crops up when moisture from a leaking pipe, humidity or condensation interacts with organic material on the concrete, such as carpet padding, drywall or paper. So put first things first: Clean up the area and then fix the water problem so the mold doesn't return. The steps to prevent mold are straightforward -- you won't have to look twice.
Get into high gear if you see a water leak or pool of water. Clean up and dry the area immediately and thoroughly to prevent further mold growth.
Inspect your home's water sources and channels to see if they're contributing to mold growth. Focus on your downspouts and your air conditioner's drain lines. If you're perplexed about where a puddle of water or condensation is coming from, call a licensed home inspector to help pinpoint the problem.
Keep indoor humidity levels below 60 percent – even better, between 30 percent and 50 percent. You can measure relative humidity with a humidity meter, a nifty instrument available at most home improvement stores. While you're at it, check appliances that produce moisture – such as your dryer and stove – to ensure that they're vented properly.
Encourage air flow by opening doors and windows when possible. Use floor or table fans to help keep the concrete dry.
Installing a whole-house dehumidifier or portable dehumidifier might be the final step for stubborn moisture problems indoors. Consult a licensed heating, ventilation and air conditioning technician to ensure that you purchase the correct size for the area you are trying to treat.