(Also see Substrates)
Masonry substrates include brick and concrete block walls. Use a rapid-setting tile mortar such as MAPEI Rapid Setting Tile Mortar to fill recessed mortar joints in brick installations prior to installing tile.
All masonry substrates should be clean, dry and free of dust, dirt, oil, grease, paint, soap, clear coats, any primers that are not MAPEI brand, old adhesive residues (unless otherwise recommended by MAPEI), and any other substance that may prevent, reduce or affect adhesion or performance.