(Also see Substrates)
Masonry substrates include brick and concrete-block walls. Use a rapid-setting tile mortar, such as MAPEI’s Ultraflex LFT Rapid tile mortar, to fill recessed mortar joints in brick installations before 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 a MAPEI-brand, old adhesive residues (unless otherwise recommended by MAPEI) and any other substance that may prevent, reduce or affect adhesion or performance.