Products recommended for hardening wood prior to final finish?

Q: I have a house which is nearly 100 years old. The sub floor is 3/4 fir, and the finished floor is 3/4 fir too. However, it has been covered by carpet for over fifty years. It came time to either replace the carpet or refinish the wood. I’m going for the refinish – and to claim it as a historical representation. However, it is fir, and soft.

I would like to use a light stain, most likely oil based, then go over with a hardener or a clear coat that will build up and add significant strength to the wood. At least enough to have couch/table and piano legs stand without damaging the wood. Do you have any products you could recommend for hardening the wood prior to the final finish or would you recommend something like the Swedish finish?

A: I don’t know of any finish that will actually alter the hardness of the wood which is controlled at least in part by how dense or tightly packed the wood cells are.

If you want an initial coat of finish that will penetrate well into the surface, you might consider Waterlox, a penetrating tung oil based product. Easy to work with but smelly and fairly expensive. Then after a coat of 2 of that, you could apply a couple of coats of polyurethane. I use Poloplaz Primero which is an excellent, tough finish. It isn’t as tough as Swedish finish. However, Swedish finish is very toxic and nasty to apply, emitting formaldehyde while curing.

The best thing to do is place some type of floor protector under the piano and heavy furniture legs such as a heavy rubber cup to prevent dents.