It is used for after-treatment of pinholes, drips, dust, and lumps. It comes in a block shape, so it can be used to sand only the top part of lumps and dust. Furthermore, using it in conjunction with compound allows you to adjust the texture and drips. (It is a wet sanding material, so please use for wet sanding.) We recommend that you round the corners with waterproof sandpaper or a file before use.