Concealed

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The sub- plaster is the lowest of a two- or multi-layer mortar layer, consisting of sub-plaster and finishing plaster , which is applied to the masonry in separate work steps. It serves as a primer on the masonry material and a plaster base for the finishing plaster.

In addition, the sub-plaster should compensate for the unevenness in the masonry and level larger holes (one speaks of plaster nests), since the actual finishing plaster is only applied in a small thickness (own grain size). Apart from flat masonry (e.g. aerated concrete and sand-lime brick), the unevenness of the surface of a wall building material is considerable. In particular with sand-lime brick elements and smooth concrete, however, it forms the actual plaster base, since the necessary connection between the wall construction material and the pure finishing plaster is not given. The very thin coating would also make the joints in the facade visible through the finishing plaster alone, because drying out and moisture penetration by external influences takes place differently in the joint area to the wall surface. If the plaster is insufficiently thick, the so-called stair cracks (cracks reproduce the joint structure of the masonry) occur again and again and form the most common complaints about defects that are easily visible when building a house.

In addition, there is the physically determined fact that climatic stresses occur, which the facade has to compensate, especially outside. These tensions can be flexibly compensated for by the flush-mounted plaster as an intermediate, softer and therefore more flexible layer.

In the case of thermal insulation plaster , the insulating additives (e.g. styrofoam balls / organic or perlite / inorganic) are embedded solely in the base plaster and are additionally protected from being washed out by rain and given a color.

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