Plastering - Condensation

Earlier in the chapter it was mentioned that one of the advantages of lightweight gypsum plaster is its ability to help prevent condensation. If the surface of a wall plastered with dense plaster is cold, then condensation may occur on its surface. Gypsum is a more porous material than lime or cement, with a much lower density and will absorb some of the moisture, releasing it when the temperature increases and the wall warms up. Because gypsum plasters use lightweight aggregates they will also improve the insulation of the wall and help to increase its internal surface temperature. However, with gypsum if the humidity is too high the plaster will become saturated and large patches of damp will appear, which are an excellent breeding ground for mould growth. To counter this occasional effect some authorities suggest that a small amount of lime mixed in with the gypsum will help to reduce mould growth.