What is Efflorescence?

When looking for evidence of moisture intrusion in a crawlspace or basement, some of the most obvious signs include water stains on the floor or vapor barrier, decay in wood, or moisture damaged framing. While these defects all point to a past or ongoing moisture issue, there is another sign of moisture problems that can be easily overlooked in both basements and crawlspaces. In this article, we will take a look at efflorescence and what it may indicate in your home.

Efflorescence (a French word meaning, “to flower out”), is a white, powdery substance that can be found on the surfaces of porous materials. Most often found on concrete or brick, efflorescence is dissolved salts that are left behind when water has moved through the porous material and evaporated, leaving the deposits behind. This can be an indicator of either minor or major moisture intrusion so its mere presence is not usually a cause for concern. However, if large deposits of efflorescence are present or if deposits are found along with other signs of moisture intrusion (such as stains, elevated moisture levels, or decay), this may indicate a past or ongoing moisture problem.

Porous materials like concrete or brick can absorb water from the surrounding area through the process of capillary action. Capillary action is extremely powerful and can transport water significant distances, which is one reason why roof leaks can be so hard to pinpoint since the area where a leak starts and where the water ends up can be very far apart. With a theoretical maximum distance of capillary rise of 6 miles, water can be transported through building materials and be moved to other areas far away.

As water is moved through concrete or brick, salt in the materials is also brought along with the water. After the water has reached its final destination and evaporates into the surrounding air, this salt is left behind on the exterior surfaces of the material. Eventually, these deposits grow and become more visible as efflorescence.

If capillary action continues over an extended period of time, this can throw off the balance of the building material and cause osmosis to re-balance to equilibrium. As osmosis occurs, water is drawn back towards the porous material to dilute the concentration. This can cause significant hydrostatic pressure, potentially leading to spalling, cracking, and flaking of the material.

While efflorescence can look like mold or mildew, efflorescence occurs on inorganic material, such as concrete or brick, while microbial growth takes hold on organic materials, such as wood or paint. While efflorescence may not always cause significant problems, it does indicate that moisture has moved through a porous material and a potential moisture problem that should be addressed.