Moisten the wood. When whiskey barrels do not have whiskey in them they tend to dry out, making the wood slots begin to pull away from one another. This leaves gaps in the seams between the staves of the barrel. Begin by pouring hot water on the outside of the barrel and letting the wood swell for a couple of hours. Once the gaps have closed, fill the barrel with hot water and let it sit for 24 hours.
Clean the wood. Use a scrub brush and wood soap to remove any mildew or dirt from the barrel. Let the wood dry and then sand the outside of the barrel to remove any disintegrating wood.
Sand the wood. Let your barrel dry after cleaning and sand the wood to remove any disintegrating parts. Make sure to sand in the direction of the wood grain.
Polish the hoops. Use metal polish to clean and polish the hoops around the barrel. This will make the barrel look much newer.
Reinforce the inside of the barrel. Saw 1/4-by-1-inch pieces of wood to the height of your half barrel. Hammer the pieces vertically on the inside of the barrel where there are any remaining gaps between the staves. If you are having trouble bending the wood to follow the curve of the barrel, you can moisten the wood slats with a little water so they have some give.
Seal the wood. Make sure your barrel is completely dry. Paint an outdoor wood sealer on both the inside and outside of your barrel. Make sure to seal right to the edge of the metal hoops so no moisture can enter the wood. This will prevent your barrel from drying out and splitting as well as disintegrating from moisture or termites.