What Is Efflorescence on Foundation Walls?
Efflorescence is a white or grayish, often powdery or crystalline deposit of salts on brick, block, mortar or concrete. It forms when water carrying dissolved salts moves through the masonry and evaporates at the surface.
Explanation
Masonry is porous. Water from the soil, rain or leaks wicks through it and picks up soluble salts from the cement, the mortar or the ground. When that water reaches the surface and evaporates, the salts stay behind as a crust. In a crawl space you'll usually see it on the inside face of the foundation walls and piers, sometimes as a horizontal band where wet masonry dries out.
The National Park Service describes efflorescence as more unsightly than harmful, but notes that it shows water has entered the structure. The bigger concern is subflorescence, where salts crystallize just beneath the surface. Federal preservation guidance warns that this can cause the masonry face to flake or spall over time.
How to tell it from mold: efflorescence sits on masonry, not wood. It is crystalline or chalky, and it usually dissolves or brushes away with water and a stiff brush. Mold grows on organic material like wood or paper, often in fuzzy patches or spots. If you're not sure, have it checked.
Cleaning off the deposit doesn't fix anything if water keeps moving through the wall. Federal guidance recommends finding and controlling the moisture source. Typical fixes include gutters and grading, exterior dampproofing where the outside grade is higher than the crawl space floor, interior drainage, and a sealed wall liner as part of a closed crawl space.
When to seek help
- The deposits keep coming back after cleaning, or they are spreading.
- The masonry surface is flaking, crumbling or spalling.
- Efflorescence shows up along with standing water, damp soil or high humidity.
- You see cracks, bowing or mortar washing out of the joints.
See crawl space waterproofing or crawl space repair, and read 7 signs of a crawl space moisture problem.