The typical way of efflorescence removal is brushing and sandblasting. It works but most often, along with the efflorescence, sand erodes the bricks and mortar with its abrasive force which can damage the structure as well as architectural beauty. So one has to be conscious while sandblasting.
Another alternative solution is using a chemical cleaner. Normally presoaking and post washing are required with clean water. Presoaking is done to saturate the wall or the structure before using a chemical solution. Presoaking limits the pores or capillary length of the structure with water. This is important because most of the chemicals are acidic in nature and can damage the structure. As presoaking limits the capillary length, acid cannot reach depth to structure. After chemical cleaning, again washing with clean water is also required. A muriatic acid solution is typically used as the chemical cleaner.
But one thing to remember, these only cures the symptoms temporarily, not permanently removes the causes of efflorescence. So after acidic treatment, efflorescence may appear again. You have seen the efflorescence, it means there is a source of water from internal or external with salt and you have to prevent that cause.
Figure 4: Removing Efflorescence [image credit: Youtube.com]
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And last, of all, it is safe to approach non-acidic cleaner first because some surface can be sensitive to acid. Starting can be with a stiff brush. It’s best to wear a respirator, safety glasses, and gloves. The acidic cleaner is dangerous to people as well the surface, so it is always safe to entrust the job to a specialized contractor. Because it is always better safe than sorry!