We've all seen it: that really ugly white powder that grows on cement grout and also tile, stone, brick and concrete, particularly when it's installed someplace with moisture (i.e., in a basement or outdoors). That white residue is called efflorescence.
What Causes Efflorescence?
Efflorescence for Inspectors explains that,
"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."
You might hear it referred to as "new building bloom" or even "whiskers."
According to the Portland Cement Association Trowel Tips information sheet of Efflorescence (downloadable PDF),
" A combination of three common circumstances causes efflorescence:
- soluble compounds (i.e., salts) in the masonry or adjoining materials
- moisture to pick up the compounds and carry them to the surface
- evaporation or hydrostatic pressure that causes the solution to move
If any one of these conditions is eliminated, efflorescence will not occur."
Efflorescence, then, happens. As a professional tile installer, your role is to anticipate such situations so as to prevent it from occurring.
Figuring Out Why Efflorescence Happens
Tile installers are often called on to look at challenging installation opportunities and also use their expertise to solve problems when they occur. Finding the solution can be difficult, and sometimes we scratch our heads and say, “Why is it doing that?”
Many times installers are asked to install exterior tile on a job that appears to be elementary. Unfortunately, some of them develop issues at a later date.
Take for instance a job calling for a natural stone to be installed on the exterior wall of a new retail store which has a roof above it.
The plans call for the stone tile to be installed over a waterproofing membrane coating the cementitious backer board on steel studs. It sounds routine and it should function well; which it did in this case, for about a year.
Sometimes Efflorescence Isn't the Fault of the Tile Installation
As time passed, the owner began to see a white powdery substance growing on the grout joints. Immediately the call goes out, “There is something wrong with the grout.”
Upon investigation, the grout had not failed, but a naturally occurring mineral salt which is present in all Portland cement products (thin set mortars and cement grouts) had found its way to the surface. This salt deposit is called efflorescence.
Normally, these residues can be washed away with a very mild acid solution and a bristle brush while being careful not to harm the stone (always test first to be certain the acid will not alter the existing finish). It this case it worked… for a little while. Continued scrubbing removed the salts, but it kept coming back. What was the cause?
For efflorescence to occur on the surface as seen in the photo above, water must be present to carry the minerals to the surface, evaporate and let the salts behind.
You may say, “It was the rain water going through the grout joints.”
The rain could have been the culprit, but not in this case. Remember, there was a roof over the tile.
The problem was actually caused by the roofer who failed to properly install the metal cap flashing on the parapet wall above the roof. The water went through the defective flashing, down through the thin set mortar to the lower portion of the wall and blossomed on the grout joints.
Once the tile installer (now a forensic specialist) found the problem, the roofer made the necessary repairs, the tile installer washed away the salt deposits and magically the efflorescence disappeared.
In this example, defective roof flashing led to excessive moisture, which in turn caused that ugly white powder on the grout joints and tile.
In another situation, the problem could be the result of moisture from the soil under a basement floor or wall and might require a vapor migration membrane instead.
The important point is to find the source of the problem and solve it so efflorescence doesn't reoccur. This is what identifies a true tile installation professional.
Have you encountered problematic efflorescence situations? How did you determine the source of the problem and how, then, did you address it in your installation? Let us know in the comments.
Additional Resources on Efflorescence:
- How Efflorescence Works
- White Residue on Grout from TCNA
- Efflorescence Causes, Removal, and Prevention