Academy Notes and Tips
the Shopsmith Woodworking Academy
The messiest, most dreaded job in all of wood finishing is refinishing - the stripping off of an ancient, ruined finish in preparation for the application of a new one.
Yet, believe it or not, when done properly, it can also be one of the most rewarding jobs in wood finishing. Somewhere under those 37 layers of cracked varnish and wrinkled paint is the patina…a thin layer of beautifully aged wood, just on the surface of your object. If you can carefully strip off the old finish without disturbing this delicate layer, your refinished project will take on a glow and warmth that only the passing years can bestow on the wood.
Chemical stripping is the messiest of the two. With this method, the old finish is coated with a substance that softens it and turns it to a goo. Then, you usually remove this goo with a putty knife or scraper and try not to get it all over yourself in the process. It may not be fun, but chemical stripping is the best way to remove a finish without disturbing the patina of the wood. Only the finish comes off - not the wood.
Mechanical stripping with scrapers, sandpaper and sanders is a lot less messy and (if you use a belt sander) sometimes faster. However, you'll have to be extremely careful not to scrape or sand into the patina of the wood. If you do get down to the wood and you find that it starts getting lighter and lighter in color as you go, STOP! When lighter wood shows, it means you've cut through the patina…and that's not good!
By themselves, one method or the other is usually inadequate for most refinishing jobs. Most refinishers use both methods in varying degrees, depending on the project. Let's look at each.
THE CHEMICAL STRIPPING
There are two types of chemical strippers - caustic and solvent. Each is designed for a different use. Caustics have a water base. You spread them on the project, wait for them to work, then wash them off with soap and water. But water may raise the grains of some woods and ruin plywoods and veneers. That's why you should use caustics only on solid, close-grained woods. On other materials, use solvent strippers. These typically have an alcohol or petroleum base and won't harm your more delicate projects.
Since most chemical strippers are purchased ready-mixed, follow the manufacturer's instructions TO THE LETTER when using them. Here's the general method of application:
Using an old, cheap brush, apply a liberal coat of stripper over the entire surface of the project. Reapply, this time, working the stripper into the finish with your brush. Let everything set for 5 to 15 minutes (according to instructions), or until the old finish has softened. Test the finish with a putty knife, and when it's soft enough, scrape it away. Reapply a third time to stubborn areas and scrape again. Finally, wash the project thoroughly - with soap and water if you're using a caustic stripper and with denatured alcohol if you're using a solvent type.