What causes salt staining on plywood and how can I get rid of it?

Salt staining can appear on low build wood stained exterior grade plywood, especially on eaves and soffits. Salts are contained in the adhesive used to bond the layers of plywood together. Because wood stains are very permeable, they can bring these salts to the surface of the wood. Rainwater will normally remove these salty deposits, except in sheltered areas such as soffits and eaves. The only way to remove these deposits is to wash them down until they no longer appear. To prevent this when fitting new soffits adequate ventilation is required and coating the back of the board.