gypsum plaster on concrete

Applying gypsum plaster to concrete is considered problematic. In order to bring the two materials together without any defects, craftsmen have to strictly observe certain guidelines. With careful processing, the gypsum plaster can also be applied to a concrete substrate.

Beware of moisture

Gypsum plaster is suitable for cement-bound substrates. This also applies to concrete substrates. The surface must be absolutely dry. If a concrete wall is to be plastered with gypsum, this wall may have a maximum residual moisture of three percent. If the moisture level is higher, the plaster can damage the concrete wall. Gypsum contains sulfates, which react chemically under the influence of moisture. This becomes visible through the so-called cement bacillus. It is also known under the technical terms concrete driving, sulphate driving and ettringite driving. There are cracks, bulges and even openings in the concrete. If you have planned a gypsum plaster for a concrete substrate, you should carefully check the moisture content of the substrate. If in doubt, a specialist can determine the value with a measuring device.

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This is the only way the adhesive bridge works

The concrete wall to be worked on can only be plastered if it is intact, clean and free of dust. Plastering work on concrete is not possible at temperatures below five degrees. An adhesive bridge must be applied to the concrete. Mortar (7.79 € at Amazon *) mixtures or concentrates in a bucket are available in stores. The mixtures contain quartz grain. This component is crucial for a functioning bond bridge. When mixing a dry mass with water, you should stir particularly thoroughly and ensure that the mass is evenly mixed. In practice, the individual components are always inadequately mixed. The important quartz grain does not end up in the processed bonding agent, but remains at the bottom of the mixing bucket. As a result, only the plastic dispersion layer that is also contained is then applied. In isolation, it does not form a bonding bridge, but actually acts as a separating layer.
A perfectly applied adhesive bridge can be plastered over with plaster after 24 hours, depending on the manufacturer.

Tips & Tricks Gypsum plaster is available from specialist retailers packed in sacks. Mixing should be carried out exactly according to the manufacturer's instructions. Gypsum plaster can be mixed in a bucket or in large tubs. A stirring basket is also recommended. The mixed gypsum plaster must be processed quickly.

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