At present, I'm building a sunroom addition, 16'x16'. My client wants to put knotty pine on the interior. I said, fine, no problem. I don't work too much with knotty pine carsiding, so I'm not sure what is best for a finish coat, so I guess I do have sort of a problem. She wants a clear finish, but I am not certain whether to use shellac, polyurethane or anything else. Any suggestions?