Using the trowel, start to core the stucco surface to improve adhesion to the next coat. Place lines in the stucco with the trowel in a messy fashion, crisscross lines, diagonals and so on. Tape a plastic sheet over the patch to keep it from drying out. The scratch layer should dry for a few hours. Commonly, the basic layer is allowed to dry and another scratch layer is applied on top. Let each layer dry one or two days.