Most mineral materials are based on e.g. calcium carbonate, calcium sulfate and silicates. The following materials are used for masonry: aBrick: liable to efflorescence of water-soluble salts; pH = neutral to alkaline Sand-lime brick: high capillary water absorption; pH = neutral to alkaline The following building materials are also used: Gypsum (CaSO 4 * 2H 2 O): rel. high water content; not water-stable, pH = neutral aLime (CaO), pH = alkaline Concrete (also washed concrete and gas concrete): porous concrete surfaces readily absorb moisture and are ...