Efflorescence, what is it and what causes it?

By William Decker, Nick Gromicko and Kenton Shepard 

Ahhh, springtime in Chicago.  The snow has melted, the sun is shining, the Cubbies have started another season, the flowers are blooming and love is in the air.Efflorescence on a brick condominium building.

And, the brick buildings are covered with an ugly white powdery substance that looks like crap!

The technical name for this white powder is Efflorescence (from the French, meaning "to flower out").  It is an accumulation of minerals and salts on masonry surfaces, such as brick, cement, and sometimes stone. Building inspectors and home owners should know how to prevent  and remove this unsightly residue. They must also be aware that, while efflorescence in itself is not a problem, it is a symptom of a problem, namely the presence of excess water in the masonry, which can lead to more serious structural and health issues. 

How Efflorescence Forms

The actual process of efflorescence formation is best understood by a very applicable analogy.

As an inspector, I regularly go up into the attics of houses.  During the summer, it is not unusual for the temperature in these attics to run around 160 - 165 F.  Long story short, I sweat alot because of this.  I wear a cap (below) to keep insulation out of my hair, bit it also acts to absorb the sweat from my forehead and keep it out of my eyes.  This sweat (which is just salt water) is wicked up the cotton fabric of the hat and the water evaporates.  As it does, it leaves the salt behind, creating white stains on the cap.  This is the human form of efflorescence.

Efflorescence on sweaty cap

Like humans, all masonry building materials (brick, cement, stone, stucco, mortar) contain natural salts (mostly, sodium and calcium chloride). These salts remain trapped within masonry in solid form until they are dissolved. When dissolved in water, they make their way out of the material through small pores in the masonry. The water can originate from rain, sprinklers, household leaks, or any number of other places. In the winter, the heat in the building will move outward and drive this moisture in front of it as it causes the water to expand.  When the water / salt solution reaches the exterior wall surface, the cold, dry air will evaporate the water, leaving the salt as a white crystalline growth on the surface.  Efflorescence typically forms during cold, dry weather which is when masonry buildings do most of their drying out.  It can occur year-round, but it is most likely to form during the winter due to low temperatures.

Identifying Efflorescence

As with mold, the appearance of efflorescence varies greatly. It can be powdery, it can have sharp edges and be easy to spot, or it can have indistinct edges. It can cover a large area as a fine dust, or form large individual crystals. Its appearance depends partly on the type of salt from which it is composed, but also on humidity levels (both inside and outside the house), and local rainfall and winter temperatures during the last few years. In exceptionally dry climates, water can evaporate before it even reaches the surface, in which case the salt will accumulate unseen beneath the surface. In humid areas, moisture may take a long time to evaporate, allowing the slow growth of “whispers” projecting from the surface.Water intrusionpoints in masonry walls 

Typical masonry wall detail

Professional InterNACHI inspectors already know how to distinguish mold from 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. Here are a few tips that inspectors can offer their clients so that they understand the differences:

- 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.

Aside from mold, the following problems can also result from excess moisture in a building:Tjermal image of water in masonry blockMasonry block wall

- Fungi that rot wood (including structural members like floor and roof joists);

- Water damage and staining to drywall and wooden trim;

- Water leaks above windows;

- Reduced effectiveness of insulation.

Inspectors should note the presence of efflorescence in their inspection reports because it generally occurs where there is excess moisture, a condition that also encourages the growth of mold. An exception can be made during the first few years of a building’s construction when efflorescence will appear as a result of moisture locked within the masonry in a process called “new building bloom.” This moisture comes from water added during the manufacturing or mixing process that will undoubtedly contribute to efflorescence. This type of efflorescence will appear all over the masonry material and will continue to accumulate until the initial water supply is exhausted, which can take up to a year. Efflorescence that appears locally and after the “new building bloom” is over is a symptom of excess moisture that can be problematic. The source of this moisture should  be determined and corrected.

Using Efflorescence to Diagnose Building Problems

Since efflorescence is the result of water leaking the building's surface, it can be used to diagnose the source of water intrusion problems, structural issues and construction defects.  A skilled Home Inspector uses efflorescence to check for these things.  The areas of efflorescence formation, its shapem extend and direction of wicking, as well as the salt composition moisture of the efflorescence.  As seen in the photo at the top of this page, this building is having water management problems.  There was moderate water staining seen on the interior walls, especially at the two front corners (each floor had 2 condominium units, side by side).  The efflorescence patterns, the exterior stone trim  was installed so as to bridge the usual air gap between the exterior brick veneer and the interior cinder block structural wall.  This prevented water that would penetrate the brick from properly draining down the air gap and concentrated moisture in the trim stone.  This information greatly simplified the scope of the repairs for the condominium association.  It is always better to diagnose and understand problems before you try to fix them.

Prevention and Removal of Efflorescence

Brick walls with properly installed joist flashing and weep wicksPrevention:

- An impregnating hydrophobic sealant can be applied to a surface to prevent the intrusion of water. For brick, a silicone based penetrating sealer is best. For cement block, an elastomeric or polyurethane based "plugger" type paint will surface seal and last much longer than a penetrating sealer.  These products will also prevent water from traveling to the surface from within and entering the wall from the outside. 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.  Masonry work should only be done by qualified, trained, licensed and insured professionals who are aware of the local weather conditions and the proper methods to install masonry, based upon those conditions.  As with all things in life, quality costs more.

- Also during construction, care should be given to properly flashing, completely, under the coping stones and at the floor joist pockets and exterior stone window sills and trim.


- Pressurized water can sometimes be used to remove or dissolve efflorescence.

- A mild acid solution, such as white vinegar or diluted muriatic acid (ONLY TO BE USED BY PROFESSIONALS!  THIS STUFF IS SERIOUSLY DANGEROUS!), can be used to dissolve efflorescence. Water should be applied first so that the acid does not discolor the brick itself. Following application, a baking soda solution can be used to neutralize the acid and prevent any additional damage to the masonry. Muriatic acid is toxic, and contact with skin or eyes should be avoided. 

- A strong brush can be used.

Please note:  The use of water to remove efflorescence may result in the re-absorption of crystals into the host material, from which they may later reappear as more efflorescence. It is advisable that if water is used in the removal process that it is dried off very quickly.

In summary, efflorescence is a harmless yet unsightly accumulation of salts on masonry surfaces. Its presence indicates excess water, a condition that can damage interiors and encourage the growth of mold. Inspectors should know how to remove efflorescence from surfaces, and educate their clients about its identification and significance.