The purpose of pressure cleaning is to remove chalky residue, dust, loose stain or paint. We recommend performing the pressure washing a few days, weeks or even a month before painting. Pressure washing also removes cobwebs, and oxidization that would other wise be embedded in the paint. Pressure washing is a great way to ensure proper adhesion to the primer or stain. In recent years we have seen more acid rain and pressure washing is not always needed in areas where the substrate is bare or in a solid state, but it's generally a good idea and the fastest way to get a clean substrate.