We've all seen it: a chalky white substance showing up on the surface of brick, block, or even mortar. It's often called New Building Bloom as it usually shows up on new construction, and some people can mistake it for a myriad of things, from excess mortar or concrete to paint, to acid stain, to even mold. We're here to clear up what is and what isn't efflorescence, how to identify efflorescence versus other stains, as well as how to deal with efflorescence if it's a problem on your job site.
More information and further reading on efflorescence can be found in articles by Masonry Magazine and in BIA Tech Notes, which we will provide at various sections and at the bottom of the article. For a full list of the BIA Tech Notes, visit this link.
What is efflorescence, and how to I prevent it?
Efflorescence is the manifesting of water soluble sodium, or salt, on a porous surface. When water enters a brick, mortar or concrete, the water can dissolve salts inside the brick and carry it to the surface, where it will eventually dry and form a chalky white powder. Efflorescence is much more likely to appear on concrete than brick and mortar, and it's more likely to appear on mortar than brick. More often than not on a brick wall, the mortar is the culprit. It's rare (though not impossible) for bricks to effloresce, as bricks are tested by the manufacturers for efflorescence before being sold, though mortar and concrete are not.
At its core, efflorescence is harmless. Salt does not harm the masonry or the mortar, and is easy to remove. Typically efflorescence is a temporary problem and only an aesthetic issue, and the efflorescence will go away all on its own after the soluble salts are worked out of the masonry.
However, if the efflorescence doesn't go away naturally and is recurring, it can indicate problems elsewhere in the wall system. Diagnosing problems in wall systems that can cause recurring efflorescence is beyond the scope of this article, however below we have included the Brick Industry Association Tech Note about the cause and prevention of efflorescence that may help in diagnosing these issues for you.
The best way to stop efflorescence is where it begins; not letting an unnecessary amount of water into the wall system. Efflorescence typically occurs on new buildings due to the building materials becoming more wet than expected during construction, due to weather, improper storage methods or other factors.
When building, be sure to keep building materials off the ground and stored in ways that prevent rain or snow or contamination by dirt, plants, organic materials and groundwater. Use water that is potable, clean and free of salts, acids alkalies or organic materials when creating mortar or grout. Be sure to completely fill all mortar joints when building the wall and preventing mortar droppings in air spaces. Cover unfinished masonry work when the days work ends or during inclement weather using water repellent tarps with two feet of leeway that are weighted to prevent them from becoming uncovered.
For further reading on the causes and prevention methods for efflorescence, please read Tech Note 23a: Efflorescence - Causes and Prevention.
Additional information on construction procedures for protecting walls during inclement weather can be found in Tech Note 1: Hot and Cold Weather Construction.
Identifying efflorescence against other stains
As said previously, efflorescence is a white (or sometimes yellowish) chalky substance that's essentially just salt, carried by water from the masonry to the surface where it dries and forms a crystalline sodium structure. However, there are a few kinds of stains that are easily mistaken as efflorescence, or visa versa.
Efflorescence typically looks like a floury substance, like a powdered donut. In most cases, it appears around mortar joints and won't appear to be running down the masonry surface. If you see it running, you might have lime run. If the stain appears to be around the center of the brick, then you might have white scum. Efflorescence most often looks as if flour is thrown on a wall.
The easiest test to see if a white stain is efflorescence, rub your finger on the stain (if possible) and if it rubs off to your touch on your finger, it's more than likely efflorescence. You can taste it and if it tastes salty then it's efflorescence, as white scum will have an acidic tang and lime run isn't salty.
The second easiest test to see if it's efflorescence versus other white stains is to spray down the stained area with water. If the white stain disappears, then it's efflorescence. If the stain doesn't, then it's either white scum or lime run.
Lime run, despite its name, is actually caused by calcium carbonate deposits, not lime. Lime run typically runs down the surface of the masonry, and is white or grey with a thick, crusty appearance, not powdery like efflorescence appears to be. The same property of calcium that creates stalactites and stalagmites in caves is what creates lime run, as water carries calcium to the surface in the same manner as efflorescence, but when the calcium appears onto the surface and encounters carbon dioxide in the air it hardens into calcium carbonate and is no longer water soluble. As such, lime run will not disappear when wet. When lime run appears, it typically does not stop and will only worsen over time until the source of the water is dealt with, and typically has to be removed with buffered muriatic acid.
White scum is a silicate deposit that causes irregular shaped white or grey discolorations on the surface of the brick, or it can cause the discoloration over the entire brick surface. White scum is caused by improper cleaning of brick, whether using the wrong product or using the wrong cleaning methods. Using unbuffered hydrofluoric or hydrochloric acid for cleaning can (and often will) cause white scum, or using other chemical cleaners can cause it as well. Inadequate prewetting of the masonry surface before cleaning can make buffered acid cause stains as well. When the acid interacts with the masonry, it dissolves components of the masonry and mortar where the silicate appears on the surface and isn't water soluble. If you aren't careful, improperly cleaning off one stain can cause white scum, which is even more difficult to remove.
There are other kinds of stains that can appear on masonry, but these aren't often mistaken for efflorescence. Vanadium stains are green, yellow or purple in color, and manganese stains are brown. Other colors of stains can appear, but these are usually caused by other materials such as rust, copper, hard water or paint runoff, or biological growth like mold or algae.
For further reading on masonry stains and efflorescence, please read Tech Note 23: Stains - Identification and Prevention.
How to get rid of efflorescence
Typically, you don't need to actually get rid of efflorescence, as a majority of cases where efflorescence appears it goes away in short order due to rain and natural erosion. However, in areas where it is typically very dry such as the southwestern United States, or if the appearance of the building must be carefully maintained, then efflorescence is easily removed.
Efflorescence can be removed with a soft bristled brush, water and some elbow grease. No acids or harsh cleaners required, just water and scrubbing. Do not use a metal scrubbed or any hard bristled brush, as this can etch the surface of the brick. For the same reason, do not use a power washer.
However, as said previously in this article, if efflorescence persist and reappears for an extended period of time, you might have a compromised wall system where water can easily enter.
For further reading on masonry stains and efflorescence, please read Tech Note 20: Cleaning Brickwork.