A white or grey haze may appear on older walls, even after decades. This is known as ‘gypsumization’. Small crystals of gypsum (calcium sulphate) are deposited on the surface of the bricks. Gypsum is not soluble in water and will therefore not wash off with the rain.
Although not harmful, it can form an ugly haze.
You can remove gypsum using a high-pressure cleaner. In severe cases, blasting methods need to be used.
After cleaning the façade, treat the entire wall with WP7-401 Façade Waterproof. This ensures that no new moisture can penetrate the façade, and no new efflorescence can develop.
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