Another question..What sander is recommended - Orbital or belt and what grit to start with?

Hi, you should see if rubbing alcohol takes the old finish off (in an out of the way place). If it does, it's shellac. If the finish and color is in good condition, I sure wouldn't sand it (old house forum can advise - dings and scratchs in shellac very repairable.) Poly can go over shellac as long as there is NO WAX IN, or ON TOP OF the shellac.

If you have to remove it get what you can off by softening it with denatured alcohol and using a scraper on it when it's soft, and then sand only to get a smooth surface. Otherwise sanding shellac can be a mess - it gums up the paper and the friction can cause black scorch marks in the wood that can't be removed (been there done that).

The guy in the floor store recommended Bona deep tone sealer(DTS) for my 100 yr old fir, and I was skeptical - till he explained that the slightly brownish/amberish tint helped even out the tone and bring out the beauty of old fir. I couldn't be happier with how they turned out - a deep rich honey color.

This post was edited by kashka_kat on Wed, Oct 30, 13 at 20:18

Fisrt step is to test for lead. Old fir with paint is a red flag for lead.

A drum sander makes quick work of sanding but requires skill to do it properly.
Im not a fan of the square vibrator sanders. But they can do well after everything is flat and to finish things off.

You should end with 100grit or 120 for the final sand. What you need to start with depends on the old finish. With the age plan on doing three rounds. But you might be able to do 2.

Start with 50 or 60 grit and if that gums up drop down to 36. If that gumes up go to 16. If you go 16 then you should go 16, 36, 50, 100.