by Nick Gromicko and Ben Gromicko, InterNACHI
Efflorescence is the white chalky powder that you might find on the surface of a concrete or brick wall. It can be a cosmetic issue, or it can be an indication of moisture intrusion that could lead to major structural and indoor air quality issues. A home inspector should understand what efflorescence is in order to recognize potential moisture problems.
Indications of Moisture
Efflorescence (which means “to flower out” in French) is the dissolved salts deposited on the surface of a porous material (such as concrete or brick) that are visible after the evaporation of the water in which it was transported. The moisture that creates efflorescence often comes from groundwater, but rainwater can also be the source. Efflorescence alone does not pose a major problem, but it can be an indication of moisture intrusion, which may compromise the structural material.
Porous Building Materials
Concrete, wood, brick, stone and mortar are porous materials that contain salts. The ground in which these materials can come into contact also contain salts. Capillary action can literally suck water and transport it through porous building materials.
When the capillary flow of water reaches the surface of a building material, evaporation occurs. As the water evaporates, salt is left behind. As this evaporation of capillary flow continues, the salt concentration increases, which creates an imbalance, and nature abhors imbalance and always wants to put things back into equilibrium. This is process is called osmosis. To re-establish equilibrium through osmosis, water rushes toward the salt deposit to dilute the 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.
Here are some examples of how that pressure translates:
- diffusion vapor pressure: 0.3 to 0.5 psi
- capillary pressure: 300 to 500 psi
- osmotic pressure: 3,000 to 5,000 psi
As you can see from the list above, 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.
When efflorescence leads to strong osmotic pressures—greater than the strength of the building material—and 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.
Both efflorescence and spalling can be prevented with capillary breaks, such as by installing a polyethylene sheeting under a concrete slab.
InterNACHI inspectors should already know how to distinguish between mold and efflorescence, but it is possible for homeowners to confuse the two. The expense of a mold test can be avoided if the substance in question can be identified as efflorescence.
- Pinched between the fingers, efflorescence will turn into a powder, while mold will not.
- Efflorescence forms on inorganic building materials, while mold forms on organic substances. However, it is possible for mold to consume dirt on brick or cement.
- Efflorescence will dissolve in water, while mold will not.
- Efflorescence is almost always white, yellow or brown, while mold can be any color imaginable. If the substance in question is purple, pink or black, it is not efflorescence.
- If you dab a bit of the white chalk on your tongue and it’s salty, it’s probably efflorescence.
- fungi that rot wood;
- water damage to sheetrock; and
- reduced effectiveness of insulation.
Prevention and Removal of Efflorescence
- An impregnating hydrophobic sealant can be applied to a surface to prevent the intrusion of water. It will also prevent water from traveling to the surface from within. In cold climates, this sealant can cause material to break during freeze/thaw cycles.
- During home construction, bricks left out overnight should be kept on pallets and be covered. Moisture from damp soil and rain can be absorbed into the brick.
- Install capillary breaks, including polyethelene sheeting between the soil and the building material, such as concrete.
Pressurized water can sometimes be used to remove or dissolve efflorescence.