Corrosionpedia defines Joint Lap The most frequent joints are full-lap and half-lap joints. No material is removed from any of the pieces in the full-lap procedure, and the resultant junction is the combined thickness of the two. Lap joints can be either temporary or permanent. A temporary lap joint is used while the pieces are being fitted together. It must be removed to finish the project. A permanent lap joint is glued or welded in place. They cannot be removed without destroying the piece. Lap joints are commonly used for their aesthetic appeal as well as their functionality. Because there is no sharp edge to catch clothing or hair, lap joints are popular on furniture where appearance is important such as sofas, love seats, and chairs. They're also useful if you want to divide one large piece into several smaller ones, which is easy to do with lap joints. There are two types of lap joints: closed and open. With an open lap joint, the ends of the laps are visible and require finishing (such as sanding) before they are covered with paint or stain. With a closed lap joint, the outer edges of the laps are hidden behind other materials (such as the back of a chair). The type of lap joint used depends on how the piece will be used. If you plan to cover the lap joint with paint or another finish, then it should be open.