What is the best way to remove 45 year old stain off bookshelves?

Whether or not stained wood needs to be stripped depends on whether or not the wood was varnished. If it's particularly old wood, it may be hard to tell, but you should be able to feel a smoothness to the wood if it's been varnished. Unvarnished stained wood will retain some of the roughness of the original wood. Regardless, there are steps you'll need to take to ensure your new paint adheres to the old surface.

Stripping Varnish

If the stained wood has been varnished, then you're going to need to strip off the varnish. There are a variety of stripping products available that work great. Just have putty knives, metal picks, plenty of rags and ventilation available before you start. If the wood can be moved, take the work to your garage or porch. If not, then lay down drop cloths to protect your floors, and mask off adjacent areas with painter's tape. Allow for a few days work to get the job done right. Getting all the varnish off will save you headaches in the long run, even if the process takes longer than you'd like.

Clean with TSP

If the wood isn't varnished, it will still need a good cleaning. Use a TSP cleaning agent available at most home centers. Follow the directions on the bottle. Again, if you can move the wood to your garage, porch or patio, do so. If not, just take care not to damage your flooring or the walls around the wood you want to paint. Be sure to get all the excess TSP off the wood, and allow it to dry completely after cleaning. Lightly sand the surface of the wood, and thoroughly brush away any dust.

Apply Primer

Applying oil-based or shellac primer is a required step when painting over stained wood. Stain is oil-based, so latex primers won't adhere to it properly. You'll need to allow about two days of drying for an oil-based primer. Shellac primer dries in a couple hours, but for best results let it dry overnight. Stain colors have a habit of seeping through paint, so ask your paint supplier to tint the primer to the same or similar color as the stain you're painting over. One advantage to using a shellac primer is that it will be easier to paint over with a latex paint. If you use an oil-based primer, you'll have to rough up the surface of the primer so the latex paint adheres better.

Ready to Paint

You're now ready to paint the wood. You can use latex-based paint for this step. However, some people like the shine that oil paint provides, though it takes longer to dry. If you're painting cabinets, trim, doors, bathrooms, you might want to take the extra time and use oil. Not only will you get that glossy look, it's more durable as well. Anticipate two coats, even with primer. Some dark stains are notoriously difficult to cover.

http://homeguides.sfgate.com/stained-wood-stripped-before-painting-73064.html

I would sand them down if you want to restain them, or if you want to go the paint route there are so many low prep and no prep paints out there that would work. Many, I have not yet used myself, am sure other Hometalkers will offer some great suggestions.

They make paint stripper that removes stain too. Read front label. I use fine steel wool after using a scraper first. It might take multiple applications. Then sand smooth, and restain when dry and run a tack clothe over to get dust off. If the wood is stained after removing the stain, I use wood bleach to get a clean pallet. It is hard work, so depends on how much you want to stain it.

Great comments & ideas Ladies! one comment: don't be afraid to use a variable speed orbital sander, you can adjust the speed & get more work done than with a palm sander! Happy Projecting!

The first thing todo is sand down the bookcase. Then decide if the wood looks good to stain, if not prime it and paint (or my favorite is milk paint) with your favorite paint/color. It will change the look and feel of the bookcases which could be a beautiful new addition to your room.