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What is it?
Efflorescence in concrete happens when moisture causes soluble salt within the concrete to rise to the surface. When the moisture evaporates, it leaves behind a white, powdery substance on the top layer of the concrete. Efflorescence that becomes trapped under sealer is unsightly and is even more conspicuous on darker floors.
Is it harmful?
No, efflorescence itself does not damage concrete; it is a harmless cosmetic issue. However, efflorescence can be a sign of a moisture problem within the concrete or a larger structural issue, and if the underlying moisture isn't addressed, it can lead to more serious problems like spalling (deterioration of the concrete surface), mold growth, or damage to coatings and finishes.
Other factors that can contribute:
Poor Drainage - Insufficient drainage around a concrete slab can lead to rising groundwater that moves through the concrete.
Cold Weather - Cool temperatures can slow evaporation rates, allowing more moisture to reach the surface and leave salt deposits behind.
High-Slump Concrete - Concrete mixes with excessive water ("high slump") are more prone to efflorescence because they bring more salts to the surface.
Poor Finishing Practices - Adding excessive water to a concrete mix to make it easier to place or finish can contribute to efflorescence.
Common cleaning methods:
Dry Brushing - The most straightforward way to clear concrete of efflorescence is to use a dry brush or rotary scrubbers and give the surface a good cleanse. If the salts are loose enough, this should do the trick to clean the area.
Light Water Blasting - Using water to clean efflorescence may sound counterintuitive, but water blasting is a quick and effective way to clean concrete pavers. Just make sure to dry the material completely afterward, as failure to do so will cause efflorescence to reappear.
Use A Commercial Efflorescence Cleaner - Commercial cleaners containing a weak acid solution can help neutralize and remove efflorescence as well as mitigate future occurrences.
Coating the surface:
If you want to paint or apply a sealer to concrete that has efflorescence, you must fix the underlying moisture problem first. Simply covering it up will prevent the moisture from escaping, which can cause the finish to fail.
Remember...recurrent or excessive efflorescence can be a warning sign that a persistent moisture issue that needs to be addressed.
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