Re: Refinishing stained woodwork
If the original wood has been top-coated with shellac (and you can test that with alcohol as a previous poster mentioned) feel free to use shellac again for your topcoat. It's been around a lot longer than you and I for a reason--it works well in the right setting and interior trim work is certainly one of those areas.
It sounds like you have some weathered areas that no longer match the color of the original trim. If that is the case, keep reading.
I usually approach this type of problem like this: Sand the piece as much as required (you'll need to either sand through the finish topcoat, dissolve it, or use a stain capable of being applied on top of the topcoat--gel stains work very well for me in this last instance) and fix any small cracks in the wood with a stainable wood filler. Dust it off and see how far off the color is from the wood you are trying to match. Sometimes you can simply apply one coat of a stain that closely matches the old work at this stage and it's ready for a topcoat. Other times, you need several coats of the stain--be patient. This process can get fairly involved if you are really picky. Usually though, close enough is good enough. I have yet to see anyone examine an entire piece of trim with a magnifying glass and comment on slight color irregularities; this is even less likely with an older home.
If you are dead set on a polyurethane top coat, keep in mind that several companies offer stain and polyurethane combos that may simplify your job--as with any stain or finishing product, you need to test it on a scrap piece of similar wood to ensure that the old color matches with your new work (perhaps use the back of the trim). This can be a frustrating process, but take your time, let each coat dry, and sooner or later, you'll hit paydirt. I've been turning to water-based poly more often in my own projects--it doesn't smell so bad, dries quickly and I've found it to be very durable.
Hope that helps.
Last edited by renovatorforlife; 03-25-2011 at 10:37 PM.
"By the time we finish renovating the last room in this house, it will be time to start all over again."