Abstract: An expandable waterproof covering system used to protect sub surface areas of a building where the sub surface areas meet at an angle. The covering material is a sheet of expandable waterproof material such as a reinforced dual polycrepe material. Approximately in the center of the covering sheet is a pleated area with a series of folds on each side of the center. The center of the sheet is fit over the joining centerline of the two sub surfaces areas to be covered. If desired, a section of the folds may be restricted in their expansion by stitching the adjacent folds together. With this construction the lower folds may fan out to expand to cover more of the surface areas to be protected than the sections that those fold section which are restricted. This finds particular applicability to covering the outside corners of building before the final exterior veneer layer, such as brick or stone, is applied over the protective covering.