Sand paper is wrapped around a long block, which is nothing more than a long piece of flexible plastic molded for comfort used to sand the car. The extended length of the block removes the high build primer from the high spots and leaves it in the low spots. This give the panel the dead straight lines it needs for those razor sharp reflections the High Performance Finish is known for.
These panels will get another coat of the high build primer and another round of blocking to make absolutely certain that there are no waves. After that, we are ready for paint.