You can easily recognize efflorescence on walls or floors, it's often a white or grey, powdery substance on surfaces of concrete, masonry walls and floors, it particularly affected by water and humidity. Efflorescence occurs when calcium hydroxide, which is found within concrete, renderings, adhesives and grouting, dissolves upon contact with moisture. Aqueous calcium hydroxide is transported to the surface of the wall during evaporation. It occurs when reacts with the carbon dioxide in the air, forming white crystals (calcium carbonate).
