This video tutorial is in the Autos, Motorcycles & Planes category which will show you how to block sand body filler using hand bricks for a car. First repair the dent and apply the body filler. Blocks come in different sizes. Normally you would like to use the biggest block depending on the size of the dent. For a smaller dent, use a smaller block. There are different grades of sand paper. You would generally start out with 36 for a big dent. But, for a smaller dent you can start with 80. In both cases finish it off with 150. One of the precautions to be taken is not to sand too much otherwise you will undercut the body filler. Watch the video for the full demonstration.