I live in a four-story split-level house. On the third floor the family room, office, and bathroom have wood ceilings and trim. I don't think the wood has ever been treated, but I would like to protect it. I'm most concerned about the wood in the bathroom because it has only a small window for ventilation. What can I apply to the wood to protect it?
The first thing that you have to do is install an exhaust fan. Nothing will eliminate the humidity in a small room more effectively. If you are concerned about the noise an exhaust fan will produce, there are exhaust fans on the market that are so quiet that the on/off light is the only indicator that it is operating. You can further protect the wood ceiling and trim by treating it. You can apply a glossy or matte varnish, which is very safe to do inside. These finishes work well in a bathroom because they are resistant to humidity and fungus. You can also apply oil to the wood. However, the problem with applying oil is that it becomes dirty very quickly. You will find the best results with varnish and, of course, installing an exhaust fan.