Such as an exposed brick wall or a stone hearth
Prep: Scour unpainted bricks with a sponge or a nylon brush and warm, soapy water; let dry overnight before priming. On previously painted surfaces, use a wire brush to remove chips and flakes, then smooth uneven areas with 100-grit sandpaper before cleaning.
Coat: Seal pores with a water-based primer designed for masonry, and coat with latex paint. Use a thick-nap roller, and use a brush to cut in along the edges or to get paint into any crevices the roller can't reach.