We purchased a new home in Sacramento California 6 1/2 years ago. We have had a constant issue with our garage floor having an abundant amount of thick white powder substance. Our contractor states this is a normal occurance but everything that sits on the floor of the garage develops mold underneath it and the white powder outlines the shape of the item. I mean any item. Tires, tools, lawn mower, hammer, shoes, hair barrett, etc. Can this be corrected? What is an acceptable amount? Can this be causing an air quality issue? It just seems since we have been in this house, our noses are always clogged like we have colds or allergies. How do I verify that this is an acceptable occurrence? Is this happening throughout the house? etc... Need help or guidance into the right direction! We have also have a small (quarter size) hole develope towards the middle of the garage.

Efflorescence is the term for lime-salts leaching from concrete and crystallizing on the surface of the concrete. This can occur on floors, masonry walls, foundations and even soil. Efflorescence is not the problem. The root cause is moisture, and this will continue to be a problem until you address the source of that moisture. Most likely, in your case, the source is irrigation in summer and poor drainage in winter. If you have a home built on a slab, the moisture could be affecting the entire structure.

In the garage, this is not a health problem, but as you know, objects stored on the floor need ventilation under them to prevent moisture damage or mold. The same is true of any structural wood (sill plates) that are in contact with the slab. In the home, this could be a health problem if carpeting or padding is becoming moldy as a result of moisture intrusion. The best way to check is to have a section of carpet lifted to inspect the backing.

The solution is a combination of perimeter drains and/or proper grading, and avoiding excess irrigation near the foundation (a carefully controlled drip system that never causes ponding would be better than shrub sprayers).