I have an order for a wooden bathtub carved out from a huge tree trunk. While I am busy with the excavation, I will very much appreciate some help and/or ideas for waterproofing this huge tub. Many thanks in anticipation. – Alok Mital
Rob Johnstone: What an awesome and, if I might add, totally crazy idea. Are you burning out the interior of the log like the South Sea islanders do for dugout canoes?
To your question: as I see, it you have a couple of options. You could spray it with a catalyzed lacquer, which dries very hard and is quite resistant to water. A similar concept is to use clear epoxy as your finish … for the same reasons. The problem, even with these two ultra-sturdy finishes, is that they will wear over time, and the wood fibers will expand and contract over time, which means that the finish will fail at some point. Another option is just to leave the wood finish-free. As long as it gets dry between uses, it will last a long time and might be more “user-friendly” than a finish would be.
Tim Inman: If transparency is not an issue, I’d suggest one of the “below grade” two-part epoxy paints designed for tank lining and water containment areas. “Swimming pool” paint, for lack of a better description. If transparency is desired, then I’d still go with a two-part epoxy. Polyester clear or gel coat would be another option. Probably the biggest concern for failure would be simply good old wood movement. As your bathtub dries, it will move. Keeping a finish from cracking or peeling away would be my concern. Two-part polyurethane coatings are available in both opaque and clears. Although not as durable as either epoxy or polyester, polyurethane is typically more flexible. Whatever you do, coat the interior before you even think about sealing in any plumbing connections with silicone caulk. Don’t even think about it!