Efflorescence is one of the most challenging issues any concrete contractor can face, and it can become very difficult to repair. Concrete can be stained when salts and other materials will come off the concrete surface. The stains are normally white and are present in darker colors more than white or pale colors due to the contrast created by the chemical reaction. Efflorescence will be triggered by low temperatures, humidity, condensation, and rain. It can also happen when some water has been added to concrete to increase its manageability.
Causes of the Efflorescence in Concrete
The efflorescence can be happening when moisture starts to react with concrete causing some white stains in the concrete. Some surfaces and mostly stained concrete will be more susceptible to the reaction than others. These surfaces allow water to travel within the surface. You will also notice it when the salt concentration is higher in material batches. Other factors that can cause the efflorescence effect are:
- Water migration to the wall surface and its evaporation, leaving the salts impregnated in the concrete surface
- The improper rising of masonry after repointing
- Deficient mortar joints or other issues such as improper flashing, expansion joints or caulking
- Improper drainage
- Too much water added to the concrete to improve manageability
Where to Start Repairing
If you need to work or repair this issue, be sure to understand that structure aging is very much related to this issue, as the older the building, the more susceptible to have this situation. You also need to verify joints, wall material changes, or any other visible area that has efflorescence on the surface, but these white stains are not structural related.
It is my recommendation to start sealing all joints, flashings, and gaps that could allow water from entering into the substrate. All cracks need to be sealed prior to repairing the efflorescence to avoid the stains from showing up again. Parapets and chimneys are areas that should be inspected first, as these are the areas on which the problem and stains are likely to occur.
How to Remove the Problem
The easiest step to remove efflorescence is to wash the wall and scrub the area to see if the stains go away. You will need to use only clear water to avoid worsening the situation. The sooner, the better, as time will be against you if you are trying to remove these stains. It is very important to use a wet vacuum or air to remove all standing water, however, if you have tried this already and the problem is still there, then use a nonmetallic brush to dry brush the area. Once you have done that, remove salt using a scraper.
You can also try using a solution of vinegar, muriatic, or citric acid that can be applied to the affected area. Be sure to dilute some of these acids before mixing them and always wear required PPE. If you are opting for this solution to get rid of the concrete efflorescence, you will then need to apply baking soda or any other similar product to balance the acidity on the concrete surface.
There are other commercial products available that can be used to remove the efflorescence in concrete, but you will always need to make sure that all cracks and joints have been properly sealed. When using these products, always try it first on a small area to verify that it will work and will not deteriorate the concrete.
How to Avoid It
The best way to avoid dealing with efflorescence is to prevent it from happening. To minimize these issues, be sure to use a class F fly ash to reduce the amount of calcium hydroxide in the concrete. Another important tip is to have a vapor barrier installed, preventing water from the subgrade from traveling into the surface. Always make sure to apply sealant and coatings over concrete surfaces to remove unnecessary water from the surface.