Shown here is the barrel as I originally bought it. It was actually used to make wine by its previous owner. It did hold water but there were some soft spots on the bottom which lead me to believe there was rotting inside. I first labeled all of the slats and hoops.
Next I took the hoops off by tapping them off. I first used a mallet and piece of wood which is shown in the picture. It worked well until the piece of wood began to break down. Eventually I switched to the mallet and a masonry chisel used for scoring and cutting bricks. That worked much better. The hoops are compression fit so it was relatively easy to remove them. Next I removed the top to find I was correct in the assumption there was some rotting inside. I left 2 hoops on during this process so I could keep everything in place. I also numbered all of the staves to help when putting it all back together. I used zip ties and plastic to label the hoops to move the labels out of the way when cleaning them later.
Next I took the entire barrel apart and organized the staves. I sanded both the inside and outside of each one to remove the gray paint and rotting wood inside. I used several types of sanders including a wand, orbital and belt sander for this process. As I sanded a stave, I renumbered each one on the sanded section. The pictures also show a side by side comparison between a sanded and non-sanded stave. During this process I took care to only lightly sand the ends of each stave so as to not change the shape. The top and bottom of the barrel fits snugly in each of the stave groves.