White substance on the surface that looks like salt. “Frosting” may appear for any shade of paint, however, on white and light paint it is less noticeable. On facades it may look like crystallization of salts.
Causes:
Most frequently appears in covered areas (for example, under the eave and in open verandas) that are impacted by rain, dew and humidity;
Using darker paints where chalk is used as a filler;
Painting over a layer of paint where chalk has been used as a filler with a dark shade of paint.
Solution:
“Frosting” is often hard to clean off. “Frosting” may appear repeatedly, penetrating a new coat of paint. In the worst case scenario it may worsen paint adhesion. Remove the “frosting” by scraping it off with a wire brush, or by polishing it off from a wood surface with sandpaper. Then rinse the surface and prime with an oil primer. Paint the surface using a high-quality outdoor paint.