It is necessary to impose a future patch in a damaged place, carefully combining the drawing on it and the surrounding coating. The size of this patch should be slightly larger than the damaged place itself. We fix the cash on the edges with a sticky tape. With a sharp knife on the square or ruler, we carefully cut the lines along the edges of the patch, while capturing part of the existing coating. We make sure that the edges are even and not shaggy, for this the cutting tool should be quite sharp.