Chalking is the fine, powdery residue left behind when sun and weather wear away the binder in exterior paint. You’ll feel it if you run your hand along an older wall and your palm comes away dusty. New paint won’t grip a chalky surface, so it needs to be washed or primed before repainting.
Lower-grade paints chalk faster because they rely on chalk residue to keep the finish from mildewing. When we see heavy chalking, we know the old coat did not provide adequate protection, and it tells us that the new coat deserves better ingredients for longer-lasting results.