Solid Hardwood, Engineered and Laminate Flooring - Varnish or shellac on floor

When we took up the carpets on our 37 year old house we found finished oak floors in like-new condition except for a few small spots. The floor has, obviously, not been waxed. I would like to try to hand sand and blend these spots to match the rest of the floor. How can I tell if the original was shellac or varnish? Would a sealer have been put under it? What would be required to assure that the new finish adhered to the old?

It is hard to touch up a floor, it might be better to refinish the whole room.

I doubt shellac was used [denatured alchol will disolve it] Probably varnish or poly but some floor finishers did you a laquer finish.

Thanks marksr, I am sure it could not be poly because it was put on about 1970. Is there a way to distinguish laquer from shellac? The basic issue is that I want to make sure that whatever I put on will adhere properly but don't want to sand the whole floor other than a usual "between coats" light sanding with a fine sandpaper. What would you suggest?

Unless I'm mistaken, polyurathane came out in the early 60's

Denatured alchol will disolve shellac, lacquer thinner will disolve laquer. Alchol will not disolve varnish and laquer thinner will take a little elbow grease to have much of an effect on it. You should be able to recoat any of them with poly after a light sanding - be best to test a small area first, just to be sure :D

Thanks a lot. You have been a big help.