(Also see Rough Concrete, Concrete and Exterior Concrete Substrates)
Smooth concrete will have a surface texture that compares with that of a laminate countertop. Smooth concrete surfaces should be tested to confirm porosity. If the concrete absorbs water, then it is considered to be porous. Smooth, porous concrete surfaces should be mechanically abraded. Ceramic, porcelain tile or natural stone can then be installed with a polymer-modified, cement-based mortar, such as MAPEI’s Keraflex SG, MAPEI’s Keraflex Plus , MAPEI’s Ultraflex LFT, MAPEI Ultralite Mortar, MAPEI’s Adesilex P10 Mosaic & Glass Tile or MAPEI’s Ultraflex LFT Rapid. Always use a white mortar for installations of natural stone and clean the grout joints while the mortar is still soft in preparation for grouting.
All concrete substrates should be clean, dry and free of dust, dirt, oil, grease, paint, tar, wax, soap, concrete curing compounds, concrete color stains, concrete sealers, clear coats, loosely bonded toppings, 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.