Gypsum plaster on concrete

The application of gypsum plaster on concrete is problematic. To bring the two materials together without defects, craftsmen have to pay particular attention to certain specifications. With careful processing, the gypsum plaster can also be applied to a concrete substrate.

Beware of moisture

Gypsum plaster is suitable for the cement-bound substrate. This also applies to concrete underground. The substrate must be dry. If a concrete wall is to be plastered with plaster, this wall may have a maximum residual moisture content of three percent. If the humidity value 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 cemental bacillus. He is also known under the technical terms Betontreiben, sulfa rubbing and Ettringittreiben. It shows cracks, bulges and even openings in the concrete. If you have planned 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.

Only in this way does the adhesive bridge work

The concrete wall to be worked on can only be plastered if it is intact, clean and dust-free. At temperatures below five degrees no plastering work on concrete is possible. A bonding agent must be applied to the concrete. Mortar mixtures or concentrates in buckets are commercially available. The mixtures contain quartz grain. This ingredient is critical for a working adhesive bridge. When mixing a dry mass with water, you should stir thoroughly and ensure a uniformly mixed mass. In practice, the individual components are mixed again and again inadequately. The important quartz grain ends up not in the processed bonding bridge, but remains at the bottom of the mixing bucket. As a result, only the plastic dispersion layer also contained is then applied. Isolated, it does not form a bonding layer, but even acts as a separating layer.
A perfectly applied bonding layer can be plastered with gypsum after 24 hours, depending on the manufacturer.

Tips & Tricks

Gypsum plaster is available from specialist retailers in bags. Mixing should be done exactly according to the manufacturer's instructions. Gypsum plaster can be mixed in a bucket or in large containers. Highly recommended is a mixing bowl. The finished plaster plaster must be processed quickly.

Artikelbild: Noppuns / Shutterstock

Video Board: Difference Between Gypsum Plaster & Cement Plaster