Spatterdash is a mixture of one part of cement to one and a half parts of coarse sand with enough water.
The mixture is thrown forcibly onto the wall so that the impact removes the water film at the interface between spatterdash and the substrate leading to the improvement in adhesion. The spatterdash should cover the substrate surface completely and form a rough texture.
Spatterdash serves as an effective mechanical key to prevent rendering and plastering material from sliding or sagging. The roughness of spatterdash improves adhesion by providing a positive “key” for plaster to grip. The improper application of spatterdash affects the subsequent bonding of rendering with substrate.
