The House Detective: by Barry Stone, Certified Home Inspector
Dear Barry: I recently discovered about 3 to 4 inches of standing water under my house. I pumped out the water and removed the plastic sheets that covered the ground so the soil can dry out. Once the ground is dry, should I spread lime over the surface to help prevent mold? And should I also reinstall the plastic sheets? Steve
Dear Steve: Mold prevention is not necessary unless you have moisture on cellulose materials. Wet soil will not support mold growth, so there’s no need for lime on the ground.
The purpose of the plastic membrane is to prevent ground moisture from evaporating and causing humidity and condensation in the crawlspace. If faulty ground drainage causes flooding above the plastic, then the plastic serves no useful purpose and does not need to be replaced.
The primary concern in this case is the drainage problem. To solve this, you should have the property evaluated by a geotechnical engineer to determine the water source and the best means of preventing future water intrusion. The engineer might recommend french drains around your home, a sump pump under or around the building, regrading of the ground around the building, or possibly la combination of these. Once this is done, replacement of the plastic membrane may be advisable, but additional foundation vents might also be needed to minimize humidity and condensation.
Finally, you should have the structural framing and subfloor inspected for fungus/dryrot or other moisture-related damage. In subareas with high humidity, rotted wood is common, and repairs can be very costly.