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Procedure for the removal of efflorescence from masonry before painting

What is Efflorescence?

“Efflorescence” is the term most commonly used to describe the deposit of crusty white mineral salts that appear on masonry surfaces like concrete, render, brick or mortar that have leached out from within the substrate as moisture migrates through it. 

As moisture moves through the substrate it dissolves mineral salts that are present in cement and concrete. When the mineral salt solution finds its way to the surface of the substrate, usually the warmest face, the water evaporates leaving behind a white deposit of crystalline salts.

Removal of Efflorescence

Initially, try to remove as much efflorescence as possible with a dry stiff bristled broom. If the efflorescence has hardened around surface cracking, then scraping with a steel scraper or similar may be required.

Using warm water can soften efflorescence and make removal easier. The use of a weak solution of hydrochloric acid (15 to 1) may also assist in effective removal. Care should always be taken regardless of removal method used to ensure that no damage to the coating occurs. 

When using acid solution, flood wall first with water and only allow the acid solution to have contact with the wall for a short time. Use acid strictly as directed by the manufacturer. DO NOT ADD WATER TO CONCENTRATED ACID.

In some cases where efflorescence is extensive and wide spread, the use of a pressure cleaner may well be of benefit, but psi should not be sufficiently high as to damage the paint coating. 

Once efflorescence has been removed, the affected areas should be allowed to dry till the moisture reading is less than 15% Wood Moisture Equivalent (WME), and then primed with Rockcote Anti Efflorescent Primer and then repainted or touched up with a suitable topcoat.

Once efflorescence has been removed, the affected areas should be primed with Rockcote Anti Efflorescent Primer and then repainted or touched up with a suitable topcoat.