I am in the process of redoing (hopefully not restoring) a church bi-fold door. The door is a panel door 9 feet long and 32 " wide. It is coming apart so a re-glue is in order. The first coat of finish on it is either shellac or varnish, not sure which. (How can you tell?) The door is at least 80 years old. One side is painted with what I believe is an oil base paint over the varnish/shellac. That finish has been on it for at least 50 years now. When I sand it there are spots that get gummy. What causes 50 year old paint to get gummy when sanded?
When I started working on it I put towels down on the saw horses to keep from scarring the varnish/shellac. Two days later I turned it over and the towels were stuck to that finish. Is that humidity causing that? That finish has got to be as old as the door. I have new paint for the painted side but now I have the other side with towel stuck in the finish. Don't know what I will do to correct that. Water is a no-no because of the spotting it will do and I hadn't planned on refinishing that side. Is there any way to do that without a complete sanding? I would like for it to look decent but it is a volunteer job. This door is one of 10. It is in a series that folds together or pulls apart for a room divider. I really don't want nine more of these to refinish so they all look the same. I know, lots of questions but I'm very curious why these old finishes are acting the way they are. I can't imagine they aren't cured after all these years.