Plaster on single-layer walls should be covered with decorative plaster or paint highly permeable to vapour. It is then admissible to use thin-layer plaster that meets this requirement, e.g. silicone and silicate plaster from the Alpol AT 370-378 range. If you expect to preserve the smooth texture of cement and lime plaster and cover cracks up to 0.25 mm in width, you can use Alpol AF 685 flexible silicone paint. The vapour permeability coefficient for this paint is enough to apply the paint onto single-coat walls.