Let’s talk about the surface of the object you are making. How smooth is it? Are the heads of the nails or screws flush or, better yet, recessed below the surface to be finished? How about saw, planer, or other machining marks to be seen? Are there chisel, knife, or other tooling signs?
The belt sander can solve some of these problems, the finish sander almost none of them. So now is the time to correct or camouflage these flaws in your work. There are a number of techniques and materials available to help you do so. Address these problems as follows:
Nail Holes. Unless the nail heads are intended to be decorative, you’ll probably want to rely upon finishing nails that are driven below the surface of the wood with a nail set. This leaves a small round hole to be filled with wood putty. Apply it with a narrow putty knife. If you plan to sand the surface, allow a small amount of excess putty to stand slightly proud of the surface; the sander will smooth it flush.
Screwheads. Screws are functional indeed but, you’ve got to admit, their heads just aren’t pretty. It is best to countersink them into the work, and to fill the resulting hole with a plug. The plug is glued in place and, once the glue has set, the top of the plug is removed with a sharp chisel or a flush saw.
Filling Cracks. Use wood putty, working your putty knife across the crack rather than with it. This angle of approach helps drive the putty deeper into the crack and make a better bond. Unless you will be sanding the entire surface, scrape off any excess putty before it dries.
Stains and Other Marks. Erase any pencil marks. If there’s any glue on the surface, make a mental note to yourself to do a better job next time of wiping it off at the moment it squeezes out of the clamped joint. A belt sander will take off glue that has already dried, but a scraper or chisel may be required to remove it from hard-to-reach spots. Stains can be bleached using commercially available products made specifically for bleaching wood. Most on the market today involve two solutions applied in sequence. Follow the manufacturer’s instructions.
Now, it’s on to the sanding process. The belt sander will take off most machining marks and will cut down adjacent surfaces that are not quite flush to smooth, even surfaces. Follow with the finish sander.
Time to pop open the paint or varnish can, grab a brush or rag, and get it done, right?
Not so fast. The investment of a few minutes of careful preparation now can make a big difference in the quality of the final product.
Remove Any Dust and Dirt. The piece must be thoroughly cleaned of any sanding dust or workshop dirt and debris. Use your shop vacuum for the first pass, but then try the old cabinetmaker’s trick: Use a tack cloth and wipe the entire surface to be painted or varnished. The tack cloth is a piece of cloth dampened slightly with a mix of turpentine and shellac, preferably one that has set awhile, perhaps in a plastic bag or a jar. It’s sticky, and will remove sanding dust and dirt. I guarantee you, even if you can’t see any surface debris on the piece, you’ll see it on the tack cloth after it’s been wiped gently over the wood.
Finish Supplies. You’ll need more than a brush and your paint or varnish can. At the very least, you’ll also need the proper solvent for cleaning up afterwards (read the can to determine whether mineral spirits, denatured alcohol, turpentine, or some other solvent will be required).
While you’re examining the can, read the manufacturer’s recommendations as to temperature restrictions, drying times, and application techniques. And check out your brush or rag, too. It should be clean and free of dirt.
Try a Test Run. Unless you’ve used the same finish before, you’d be wise to try it out on a piece of scrap stock first. The chips or samples they show you in the paint store and the picture in the catalog can frequently mislead the eye. Even the contents of the can itself may not be much help; virtually all finishes look different when dry than they do in liquid form in the container.
Apply your chosen finish to the scrap wood, let it dry, and then consider the result. Does it darken the wood too much? Is the color brighter (or duller) than you thought it would be? Now’s the time to make a change and avoid second-guessing yourself later.
Application Techniques. When finishing a flat surface, whether you’re using oil-based paints or stain or varnish, keep in mind that you must not allow one portion of it to dry before painting the rest. If you do, a line will probably be quite noticeable. On a large job, complete one section or side at a time.