Abstract: A trim strip has an angle strip with flanges meeting at an elbow and is covered with a paper strip having a tearaway wing extending laterally beyond one of the flanges at a line of perforations. The wing can be folded back at the perforations over the adjacent flange to project away from the elbow to provide a masking portion which can be severed at the perforations by pulling on the masking portion after the masking need is satisfied.