Woodworkers Club of Houston

Home  Finishing


by Ray Lancon


How often do you hear someone say, "You did a great job sanding that project"? That's the problem with sanding. For something that takes so much time and creates so much dust, it goes unnoticed (if you do it right).
Of course, if you did a poor job sanding, it would get noticed. That's because there isn't any finish that will hide a poor sanding job (except maybe paint). Instead, a finish will emphasize and irregularities or blemishes on the surface of the workpiece (like scratches and glue).

With all the power sanders and hand sanding products available these days, you might be tempted to think another tool will solve your sanding headaches.

While these tools can help with the elbow grease, the process is still the same. And understanding this process will save you time whether you're using a power sander or just a plain old sanding block.

GETTING STARTED. Many woodworkers will put off sanding for as long as possible. But after a project has been assembled, the sanding becomes much more difficult. So we always try to get started as soon as possible.

For example, it's much easier to sand a large panel when it can be laid flat. So we often sand a panel before it's assembled in a project, and sometimes even before it's cut to final size.

We also like to sand raised panels before they're assembled into their frames. But since we don't ever want to alter the fit of a joint, we'll wait to sand the rails and stiles until after assembly.

There's something else you should think about before starting: the lighting. You may take this part of sanding for granted. But if you aren't able to see the surface of the wood really well, you may discover a scratch, dent, or spot of glue when it's too late -- after the finish is dry. So make sure your sanding area has plenty of light.

And not just overhead light. The light should come across the workpiece at a low angle. This type of light will create shadows so that any ridges, dips, and deep scratches will stand out. One easy way to do this is to hold an auto mechanic's trouble light down near one end of the surface you're sanding. Most problem areas will become much easier to see.

FIRST STEP. The goal of the first step is simple: sand out all of the blemishes. By blemishes I mean any deep or cross grain scratches as well as nicks and dents. This step also includes any burns and layout marks. The first step should be tackled with the coarsest grit you plan to use. Whether it's 100 or 150, don't switch to a finer grit until all the blemishes are gone. Switching too early just means you'll spend more time sanding.

SECOND STEP. When all of the blemishes have been removed, it's time to sand with finer grits. The goal is to make all of the scratches left by the previous sandings finer and finer so they won't be visible after the finish is applied.

Move to the next grit when you sanded out all the scratches from the previous grit. (Good lighting and close inspections are important here.) And don't skip more than one grit. In the long run you'll spend more time sanding -- not less.

EXCEPTIONS TO THESE RULES. When sanding, it's a good idea to keep the big picture in mind. But there are times when it's more efficient to bend the rules a little bit.

One rule you'll hear often is to only sand with the grain. But some times there's a lot of wood to be removed, like on an edge-glued panel with lots of ridges. In these situations, sanding with the grain has some drawbacks. It's slow. And there's also a tendency to create dips and valleys across the panel. So when there's a lot of wood to be removed, I'll start by sanding across the grain first with my portable belt sander. Don't sand any more than needed. Remember, you'll have to sand out the cross grain scratches by going back and sanding with the grain.

END GRAIN. There's another rule I bend a little. It has to do with end grain. Instead of starting with a coarse grit like 100, I sand with a medium grit like 120 or 150. This way, I'll have to spend more time on the initial sanding, but I think it's faster in the long run. Here's why.

Coarse grits are good for removing nicks and really deep scratches, but they create deep scratches themselves that have to be sanded out with finer grits. The problem is end grain is harder than face grain. So the scratches left by the sandpaper are harder to sand out.

WORN PAPER. This is a rule I always follow. I change my paper often. It's tempting to keep the paper on for just a little longer because "it's just going to sand finer anyway." But that's not how sandpaper works. As the paper gets worn, some particles may be smaller. But they're also becoming dull. So instead of finer and finer scratches, what you end up doing is polishing or burnishing the wood instead.

When should you quit sanding? The answer depends on the finish. There are two questions to consider: Are you going to stain the wood? And what type of stain are you going to use? When using a pigment stain (as opposed to a dye), you have to keep a couple things in mind. First, how much you sand affects how dark the stain will end up. A stain sits in the pores and scratches (from the sand paper) of the wood. So the finer you sand, the fewer places there are for the stain to sit -- and the lighter the final color will be. Also keep this in mind. When you're going to stain a project, everything has to be sanded to the same grit. Otherwise the wood won't absorb the stain evenly (the exception is end grain, see Quick Tip #6 below).

Another factor that determines how fine you should sand is the finish you intend to use. The thicker the finish you're going to apply, the less you have to sand. Here's why:

With oil finishes (finishes that penetrate the wood and build almost no film at all), what you end up feeling is the wood, not the finish. So if you want the surface to feel smooth, you will need to sand the wood more. In this case, I would usually sand to about 220-grit. Then, for the first coat of finish, I'd sand it in wet with 320-grit sandpaper. This leaves the surface very smooth.

With a "film finish" like varnish, the finish needs to be smooth, not the wood. So sand the wood to about 120-grit or 150-grit. This may sound too coarse, but once the finish has built up on the surface, you won't be able to feel the wood anyway. In this case, to get a smooth surface, lightly sand the finish between coats.

1) Don't sand the wood like you scrub a floor. Use long even strokes. This way, you'll be sanding in a straight line with the grain, not going sideways across the grain.

2) Sand glued-up panels and large pieces before cutting them to final size. This keeps the thickness are the edges more consistent.

3) Don't sand up to the edge of a board with a power sander unless you want to round the edges slightly. Use a sanding block instead.

4) If you're sanding with 150-grit and you find a deep scratch, don't keep sanding at 150. Instead, switch a coarser grit to remove the scratch, and then work back up to 150 and continue.

5) If you've stained a project, be careful sanding between coats of finish. And avoid the edges if possible. It's too easy to cut through the finish and remove the stain.

6) To get the end grain of a workpiece to accept a stain the same as the face grain, sand it a couple of grits finer.

7) If you're using regular sandpaper on a palm sander, load four layers of paper on the sander at one time. Then rip off the top layer when it's worn.

8) To sand in tight spaces like corners, use sandpaper wrapped around the end of a dull chisel or putty knife.

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