Leaching of lime compounds can lead to the formation of calcium carbonate or calcium sulphate on the surface of the concrete; this is known as ‘efflorescence’. Two forms occur, namely lime bloom and lime weeping.
Lime bloom appears as white patches or an over-all lightening of the surface of the concrete. This is a cosmetic problem.
Lime weeping is caused by water leaking through the concrete and dissolving calcium hydroxide from the matrix. On contact with the atmosphere the calcium hydroxide reacts with carbon dioxide to form calcium carbonate, which is precipitated on the surface when the water evaporates, generally at cracks or joints. Serious leakage of water through joints can lead to the formation of stalactites. Significant leakage may be symptomatic of a more severe problem and can lead to durability problems.