as often as it needs it...depends how much its called on and what it touches..if my gloves or vest rub on it alot ill sand it...if bare fingers touch it, it needs sanded...if it gets rained on itll need sanded...real slate calls seem to need sanded the most...maybe because its kinda soft or something i dont know..seems just sitting in my vest pocket will mess up the surface sometimes...no big deal i wouldnt leave home without sandpaper, emry cloth and a piece of scotch bright pad..