Filler compounds are used in painting to prepare surfaces. Ready-mixed fillers based on dispersion are immediately ready for use and suitable for thin layers up to approximately 3 mm. Powder-based fillers made from gypsum or cement are mixed with water and allow greater layer thicknesses. A distinction is made between fine and coarse fillers depending on grain size. Fine fillers create a smooth surface after sanding, suitable for opaque paints or wallpaper. For exterior use, only weather-resistant, vapour-permeable filler compounds are appropriate. Before application, the substrate must be clean, dry, and structurally sound. Once dry, excess material is sanded down and the surface is primed.