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Name: Larry  Pishitelli
Heading: 1.2RE:Efflorescence
What are the likely causes (e.g. cement composition, sand grading, sand contamination - e.g. chlorides, curing, porosity, etc.) of efflorescence in concrete masonry blocks, and what can be done to prevent/ minimise it?

Alan Kirby

Water infiltrates the blocks and dissolves minerals. As the water evaporates from the surface of the unit, the mineral deposits are left behind, thus efflorescence crystals grow. Although this is generally a visual problem, if the efflorescence crystals grow inside the surface of the unit, it can cause spalling. Efflorescence is usually composed of calcium sulfate or carbonate, or magnesium sulfate or carbonate. These minerals occur naturally in many aggregates and cement, and also in the water supply used to make the concrete blocks and mortar. The best way to prevent the problem is to prevent water from infiltrating the blocks after they have been installed in the structure. Whenever we see this problem, there is usually a leak somewhere that allows water to enter the block wall. Locations such as flashings on the roof and windows, cracks in the walls, joints that are not sealed properly, plumbing leaks, water vapor condensation, etc., need to be checked. Also, the weep-holes in the bottom of the walls can lead to this problem if they are blocked and prevent water from draining out of the walls. Once the source of the water infiltration has been located and stopped, the walls can be cleaned with products to remove the efflorescence, and then they should be sealed.

Larry Pishitelli

Larry Pishitelli
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