Alkali Attack | bascopaints

What is it?

Discolouration of coating in patches generally associated with bright orange, yellow, red and sometimes even the blue and green colours tinted with organic colourants. This normally occurs on fresh or patched up plastered walls. The patches can be both in shaded and UV exposed areas.

Possible Causes

Alkali attack of the coatings pigments by elevated concentrations of Calcium hydroxide salts from cement.
The former can be attributed by painting when the plaster is still damp. Moisture content exceeding 18%.
Moisture ingress from hairline cracks allowing calcium hydroxide salts to seep out and conglomerate.
The lack of a suitable alkali resistant primer.
Excessive continuous contact with moisture. Areas most affected are those near to parapet walls, horizontal landings, ground level and cracks etc.

How Can I Fix This Problem

Remove or seal the source of moisture ingress if this was the cause.
Apply a quality solvent based masonry primer after the wall has dried out sufficiently.
Recoat with a good quality exterior acrylic paint.

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