It doesn’t always happen but this usually has a lot to do with absorption. It isn’t harmful and is no cause for concern, but could be a nuisance. To prevent chalking of exterior brick, we recommend applying a top coat of Mineral Shield, 7-10 days after applying Classico Limewash. Most chalking happens inside the home where it’s less exposed to the elements that expedite the calcification process. Interior brick and all stone applications usually take longer than brick to calcify and absorb into the surface as it’s usually smoother and less absorbent, so wait 10-14 days before applying Mineral Shield.