The barrel may have defects on both the outside of the barrel and the interior. Outer defects are usually a place where there was a nail. This can be drilled out and plugged using a 3/8ths inch oak plug. Sometimes there are cracks that can be filled with a wood filler. We use a product called Plastic Wood from DAP. Typically these defects are addressed during finish sanding at about the 120 grit point. The photograph shows several plugs that were done for artistry on the drum we call “Bubbles”, and this shows a few examples. Normally you will desire the plugs to match so that they are not noticeable. For interior defects, we use epoxy. At first we were using wood filler, but on one drum it fell out during the tacking process. Luckily for us, we were just on side 1. We have always used epoxy since that time!