When you take up the old carpet from your wood stairs, you may discover a treasure, such as oak or mahogany treads that you can bring back to life, or a so-so softwood that would look better painted than refinished. You have to get the old carpet adhesive off before you can do either, and it's a job that usually calls for a combination of solvent and sandpaper.
Two Types of Carpet Adhesives
The bulk of carpet adhesives are spreadable, and although most are water-soluble, they don't necessarily dissolve in water once they have cured. The same is true of latex paint. You may also come across adhesive from self-sticking carpets. This adhesive is often foam-like, and although you use the same procedures to get it off, it's a little more difficult to remove than a spreadable adhesive.
One Solvent to Dissolve Them All
A plethora of solvents can soften carpet adhesive to make it easier to remove, and while there probably isn't one that works on every type of adhesive, a solvent made for the purpose is probably the best one to use. Such products are usually mixtures of refined petroleum distillates, and if you don't want to buy one, you'll probably have good luck with odorless mineral spirits or denatured alcohol, which is recommended for removing dried latex paint.
Because heat often softens carpet adhesive and makes it sticky, attempting to remove the adhesive by sanding it off with a belt sander isn't recommended. A better approach -- which will save large amounts of sandpaper -- is to loosen the adhesive with a solvent, scrape off as much as you can, then sand the residue.
Scrape off as much of the dried adhesive as you can, using a metal paint scraper and putty knife. Sometimes you get lucky, and the bulk of the adhesive comes off this way. If so, it may be a good day to buy a lottery ticket.
Soak a rag with carpet adhesive remover, mineral spirits or denatured alcohol. Apply the solvent liberally to the adhesive on a single stair tread and riser.
Wait for the adhesive to soften, which may take 10 minutes or more. If the solvent dies out, replenish it. It may help to cover the tread with plastic sheeting to prevent evaporation and give the solvent more time to work.
Scrape off the adhesive with a metal paint scraper or putty knife, and deposit it in a bag or bucket for disposal. Moisten the rag with more solvent and wipe off as much of the glue residue as possible.
Sand the remaining residue off the tread and riser with a palm sander and 100- or 120-grit sandpaper. Coarse paper removes the adhesive quickly, but it leaves deep scratches, so if the stairs are made of hardwood that you plan on refinishing, stick to finer paper.
Go over the tread and riser again by hand, using the same paper grit that you used in the sander, to remove the orbital marks. This step is necessary only if you plan to stain and refinish the steps. Sand with the grain of the wood -- never against it.
Vacuum the sanding dust and wipe down the wood with a damp rag. The tread and riser are now ready for painting or refinishing.