Preparing Surfaces for Finishing
Hand Work Requires Thought
Let’s get down to some basic facts. Lumber goes through a number of steps on the road to becoming a component in a piece of furniture. Typically it is sawn, jointed and reduced in thickness. Additional shaping operations might also be involved. Each of these steps leaves a signature behind and those machine marks are not a decorative effect. You really cannot leave them behind and later call them design features. They all need to be removed. How you accomplish that impacts how you finish, and what that finish looks like. Woodworkers generally choose one of two options: cutting (hand planes, scrapers) or abrasion (sandpapers). As a general rule, do as much of this work as you can after the joints are cut, but before gluing up. It’s a whole lot easier, for example, to clean up the apron on a table or the rails on a chair before rather than after they’re glued into the legs.
Admitting my Bias
In the interest of full disclosure, I am mostly a hand-tool woodworker. That is not to say that I don’t use power tools. I use them whenever they make sense. There are many times, though, when a hand tool does a job faster, more safely, and give a better result. So if the following comments lean a little in the direction of hand tools, you’ll know why.
A Case in Point: The Hand Plane
Students who have taken my classes know I hate sanding. Detest it. So I avoid sanding as often as possible. There are a number of reasons I feel this way, but the one that relates most directly to finishing is that sanded wood and hand-planed (or scraped) wood looks different. One surface has been abraded to make it smooth, and it looks hazy. The other surface has been cut to make it smooth, and it looks clear. If you don’t believe me, do the following demonstration for yourself. Take a well-tuned hand plane with a sharp iron, and plane the surface of a piece of cherry or oak, or whatever hardwood you have on hand. Plane it until the milling marks are gone and you have a nice smooth surface. Now take a piece of sandpaper of the grit you would normally use last in a sanding progression. Most woodworkers don’t (and shouldn’t) sand beyond P220 grit, so use that. Sand half the board you just planed. It will be smooth, for sure. But look at the difference between the hand-planed surface and the sanded surface, and you will see what I mean. Hold it up to a window on a bright day and look at the way light reflects off both surfaces. There is a marked difference, and I think the hand-planed surface is more appealing.
However, using a hand plane forces you to understand wood grain. Ignore that characteristic at your own peril when you approach the workpiece with a plane. Plane in the wrong direction and you risk tearing out chunks of wood, adding untold hours to your project as you wonder how to repair the damage. If you’re a hand tool user, wood grain plays a role in a lot of the decisions you make. When you’re gluing up a panel for a table top, for example, you want the grain in each part of the top running the same way, or you must change the direction in which you plane. And if you bookmatch a panel, you have introduced a grain reversal. Nothing you can do about it, so think it through carefully.
In any event, a well-tuned hand plane with a sharp iron will make short work of marks left behind by saws, jointers and thickness planers. They are most certainly worth the time and effort needed to learn to use them well. As your skills and fussiness increase, you will find that scrapers can remove the little marks left by hand planes and yield a beautiful, smooth surface.
Sanding will get rid of the machine marks, although it will be slower, noisier and much dustier. There are some woods that are really difficult to plane; any species with interlocked grain falls in this group. So plan extra time, make sure you wear hearing and eye protection and carefully plan a way to keep all that dust out of your lungs. And while you’re at it, plan some extra time to clean up the dust from your shop before you start finishing, so the little dust nibs don’t fall out of the air onto your nicely sanded and now-wet-with-finish tabletop.
If I am forced to do a lot of sanding, I allow extra time in the schedule to account for dust. Initially I try to minimize as much dust as I can by using vacuum attachments for power sanders, and by constantly vacuuming the surface as I finish hand-sanding. Typically I will sand one day, allow another day for dust to settle out of the air, and vacuum my finishing area on the third day. Finishing begins the day after.
As a rule of thumb, P220 is as far up the grit progression as you need to go on the bare wood. As long as you have done a good job and were careful not to skip grits (remember that sandpapers are a system, and they are designed to work sequentially) going beyond P220 is a waste of time. I strongly suggest that the final sanding step be done by hand rather than machine. Sand with the grain, and sand carefully. Your objective is to ensure you haven’t left behind any of those little “pig-tails” that are the telltale of a random-orbit sander.
A Final Inspection
Before you put away the sander, the scraper or the hand planes, wipe down your project with denatured alcohol or naphtha. Use the brief time before the solvent evaporates to carefully examine the surface for imperfections. I like to use a bright light to help with this inspection, either a double halogen work light on a stand, or the sun through a window. The light should come from in front of you, bounce off the work and then reflect into your eyes at a very shallow angle. This is your last chance to catch a bit of tear-out, some glue that you missed, or any other blemish that will be magnified by finishing and top-coating.
Remember Those Cut-Offs?
If you saved cut-offs from the project, treat them the same way you are treating actual project components. If you are sanding, sand the cut-offs with the same grits in the same progression. If you are hand-planing, or scraping, do the same to your remnants. This step is important, so don’t skip it. While you’re at it, start making notes about what you are doing, and write them on the cutoff – on the side opposite the one you’re planing, scraping or sanding. You will add to these notes later, so leave room to document additional steps.
In the next post we’ll talk about the assembly process and the final preparations for applying a finish.
Jeff Zens owns and operates Custom Built Furniture in Salem, Oregon. He is a frequent woodworking instructor and writer.