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Question posted - April 9 to April 13, 2018:

How do I clean off mortar smears that were allowed to cure for six months on a new architectural block building?



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From Zenith Czora of Zen Consultancy on April 17, 2018:
Three methods can be employed: wet abrasive (grit) blasting, chemical cleaning and the traditional acid cleaning. Wet abrasive (grit) blasting is less destructive than dry blasting but still will alter the surface appearance. This method can be used for cleaning walls which have aggregate exposed or are split-faced. It does not dissolve the mortar smears but removes them mechanically, which could also remove the outer portion of the masonry surfaces. Chemical cleaning is non-acidic cleaning using a cleaning solution containing surfactants that wets out the smear mortars, then soften the smears. The softened smear mortars will be easily removed by using a stiff-bristled brush followed by pressure washing with water at water pressure of 3000 kPa, nozzle angle of 15 degrees and a nozzle distance 50 cm from the wall to ensure not to cause damage to the surface. Traditional acid cleaning can be applied by using a weak acid solution ( 1 part HCl to 10 parts of water) . It may etch the surface or alter the tone of the color of the masonry wall. Strong acid may be more efficient in removing mortar smears but could cause salt formation due to chemical reaction, which is more difficult to remove. Prior to chemical or acid cleaning, the substrates need to be saturated with water to prevent any acid or chemical being absorbed into the substrate.


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Tagged categories: Mortars


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