By Brielle Ehmsen
December 28th, 2021
As you walk down the streets of New York City, you will find yourself immersed in rows of masonry-clad buildings. When you look at these buildings, you may notice that some have white powder or stains, while others do not. Why does this happen to some buildings and not others? This condition is known as efflorescence.
What is efflorescence and why does it occur?
Efflorescence is a powder or stain that is found on the surface of masonry, normally brick or concrete, resulting from the deposition of water-soluble salts. This occurs on the surface of porous materials like brick, concrete, stone, or wood through the process of capillary action. Capillary action allows water to be transported throughout a porous material. This occurs in buildings where concrete footings are poured onto porous soil.
What can efflorescence lead to?
When you add salt to porous material, it can become destructive. As water and salt are transported through the building material, the water will evaporate but the salt will remain; as the salt concentration becomes high enough, it can cause osmosis to try and reestablish balance within the building. The issue is that osmosis causes strong hydrostatic pressure, which is pressure that is stronger than the building material; this will cause the material to break and can cause spalling and cracks. Severe spalling of one material can cause the unit to crumble and fall apart.
How can you identify it?
As a building envelope consultant, when you are surveying a building and you find efflorescence on or in the building, the first thought is to determine the severity of the issue. One can ask: Is this a cosmetic issue or a moisture issue? There are a few ways to distinguish efflorescence from mold.
There are several factors when distinguishing mold from efflorescence. When you pinch efflorescence between your fingers, it will turn to powder whereas, mold will not. Efflorescence can only form from inorganic building materials and will dissolve if it is put into water. Another factor to note is the difference in color. Efflorescence is either white, yellow, or brown, whereas mold can be many different colors. Once you have clearly identified that it is efflorescence, there are a few ways to go about the removal and prevention of new efflorescence from forming.
How to prevent and remove efflorescence?
Efflorescence can be prevented and removed; there are several ways you can remove efflorescence. Pressurized water can be utilized to dissolve or remove efflorescence. If water is used on brick or another masonry, it must be dried off quickly to prevent the water from reabsorbing the crystals. Another way to remove efflorescence is with an acid. Acid is used to dissolve the efflorescence off the masonry since the composition is both salts and calcium. Water and baking soda are often used to prepare the masonry to ensure that no accidental damage occurs to the brick when the acid is applied. A strong brush can also be used to scrub off the efflorescence. These methods all vary on the severity of the efflorescence on the facade.
There are a few ways to prevent efflorescence from occurring and reoccurring. The installation of capillary breaks is one of the easiest ways to prevent efflorescence; using polyethylene sheeting between the soil and the building material will facilitate in preventing the process of capillary action and moisture being spread throughout the building. A hydrophobic sealant can also be used on a surface to prevent the intrusion of water which will help prevent avoid the movement of water throughout the building material. However, in colder climates, it is known to break the material during freeze/thaw cycles. Simply put, the best way to avoid efflorescence from forming on a building facade is to prevent moisture from entering the building material.
To best understand the significance of efflorescence, you must know that physically, efflorescence is a cosmetic issue; however, it can indicate a moisture problem. Knowing how it can form, how to identify it, and what problems it can cause will be beneficial to all building owners, property managers, and contractors, alike.