5. Conclusions
On the one hand, dihydrate crystals of the plaster must grow into the substrate in order to achieve sufficient adhesive properties. This requires certain capillarity of the substrate, and a sufficient moisture gradient between plaster and concrete. On the other hand, detachment and changes in crystal habits caused by subsequent drying must be kept at a minimum so that the gypsum/concrete bonding is not weakened. For this reason the substrate must possess sufficient capillarity; it should not, however, be too moist.
Damages at a later stage cannot be ruled out when time frames between the manufacturing process of concrete walls and the rendering phase are extremely short.
All tests on this topic were commissioned by the Federal Association of Gypsum and Gypsum Board Industry e.V., Germany (Bundesverband der Gipsund Gipsbauplattenindustrie e.V.). The authors are grateful for the interesting assignment and fruitful discussions. We would also like to take this opportunity to thank Mr. Forg (of Heidelberger Maxit) and Professor Dr. Hummel (of Gebrüder Knauf Westdeutsche Gipswerke, Iphofen) for their support.