Chalking Check

When painting a previously painted surface, it’s crucial that the surface is free from chalk residue. Chalking is a powdery film that forms on the surface of a coating. When a paint film dries, a thin layer of clear binder (resin) seals the pigment molecules within the coating. As the coating is exposed to weather and UV light, this clear film breaks down, exposing the pigment molecules. The pigment then rubs off on anything that contacts the surface. Chalking is most common on aged, oil-based coatings and poor quality water-based coatings. 100% acrylic resin used in quality water-based coatings has superior chalking resistance when compared to the alkyd resin in oil-based products. 

Rub the surface of paint with a finger or a dark coloured cloth to determine the degree of chalking. Dampen the chalking area and scrub with a detergent based wash and cloth, sponge or broom. Once cleaned and dry, rub the surface again with a dark-coloured cloth to check if all residue has been removed. If the cloth shows no residue, wipe the surface once more with a clean damp cloth and it will be ready for repainting (if it also passes a cross-hatch adhesion test).