What’s That Chalky, White (or yellowish) Powder in my Basement?

Indication of Moisture

The white (or yellowish) chalky powder that you might find on the surface of a concrete or brick wall or floor is called efflorescence.   It is an indication, or a sign of moisture intrusion or pressure that can lead to major structural damage and indoor air quality issues if it is not taken seriously.  While the powdery efflorescence itself is relatively harmless, it is a sign of pending issues because it generally occurs where there is excess moisture, a condition that also encourages the growth of mold and other fungi.

Efflorescence is the dissolved calcium (or lime) deposited on the surface of a porous material (such as concrete or brick) that is visible after the evaporation of the water which transported it. The moisture that causes efflorescence often comes from groundwater, but excess rainwater or snowmelt can also be the source. Efflorescence alone does not pose a major problem, but it is an indication of moisture intrusion in your basement, moisture which unchecked may compromise the structure or the building materials and help lead to fungal growth, such as mold, mildew and wood rot.

Porous Building Materials

Building materials, such as concrete, wood, brick and stone, are porous materials. Porous materials can absorb or “wick” water by a process called capillary action. As this moisture, or water moves through the porous material, calcium, lime and other salts can be drawn with it.

Concrete, wood, brick, stone and mortar are porous materials that contain salts. Capillary action can literally suck water and transport it through porous building materials, weakening the materials as it goes.

Capillary Action

Porous building materials are capable of wicking water for large distances due to capillary action  For example think of a tree and how a tree can transport water from its roots to its leaves. That’s capillary action.  It’s very powerful and it can be destructive.

Building materials directly in contact with soil will naturally wick the water inward and upward.  Water can begin to wick up from below your foundation footing and continue upward through the concrete or block walls all the way to the wooden structure above.

Destructive Pressures

When the capillary flow of water reaches the surface of a building material, evaporation occurs. As the water evaporates, the powder is left behind. As this evaporation of capillary flow continues, the power concentration increases, which creates an imbalance.  This is process is called osmosis. To re-establish equilibrium through osmosis, water rushes toward the powdery deposit to dilute its concentration. This rush of water creates massive hydrostatic pressures within the porous material, and these pressures are destructive.

The pressure from osmosis can create incredibly strong hydrostatic pressure that can exceed the strength of building materials, including concrete and block. In fact, osmosis can create pressure that is greater than the structural strength of concrete, which can be from 2,000 psi to 3,000 psi. The action of water rushing to the surface due to capillary action creates incredible forces that can cause materials to crack, flake and break apart.

Painted walls or walls covered with “waterproofing” cement or paint are still affected by capillary action below the surface, even though the actual moisture or efflorescence may not be readily visible.  In these instances, “blisters” or “warts” form as the powder forms a pocket below the surface of the paint, often causing the paint to flake or peel off the walls.

Spalling

When efflorescence leads to strong osmotic pressures—greater than the strength of the building material—the material literally breaks apart.  The resulting damage is called spalling. Hydrostatic pressure can cause spalling, but spalling can also be caused by freeze-thaw cycles in building materials that have a high moisture content.

Prevention and Removal of Efflorescence

Efflorescent is generally relatively simple to remove by using a stiff or wire brush.  Removal of the surface powder, however, doesn’t remove the condition causing it, so it normally returns relatively quickly.   Prevention requires elimination of the moisture source fueling the capillary motion in the building material which is affected.

Want to know what’s causing the efflorescence in your basement?  Call the experts at Everdry Pittsburgh at 877-814-6012 for a free foundation in