Efflorescence on foundation wall in crawlspaceDEAR MICHAEL: The white powdery substance that you're referring to is most likely "efflorescence". Composed mainly of salts, lime and other minerals, this substance is what is left over after water that has absorbed into the concrete has evaporated. A small amount of efflorescence seen on the interior surfaces of the concrete foundation walls in older homes is normal but it is something that should be monitored closely to ensure that it doesn't get excessive. In advanced stages, efflorescence will leech important materials from the concrete such as lime and the concrete can get brittle and begin to "spall" during which time the outer layer of the concrete flakes off and the foundation system begins to lose its structural integrity.

 

It's all about controlling moisture around the exterior of your home. There are many things that can be done to reduce the amount of moisture that is available in the soil around your house. An adequate roof drainage system to properly divert rainwater away from the ground surrounding the home should be considered. Next, take a walk around your home and check to ensure that the soil slopes away from the home. We're not talking drastic angles here, just a slight slope of around a quarter inch per foot is all that is required to allow water to passively flow downhill and away from the foundation wall. Finally, revisit the crawlspace and this time have somebody topside flush toilets, run water in the bathtub, sinks, laundry, etc. While the water is running, look at the entire plumbing system that is visible above ground and check for leaks. If your home is an older one with cast-iron pipes it is likely that you have leaks to some extent. A leaky plumbing system can add significant amounts of water to the crawlspace and this water will get absorbed up into the foundation walls making the problem worse.