by Eric Meier
1. Not enough sanding
Picture of my nightstand (tell-tale swirl marks)
In my very earliest days of woodworking, I used to think that sanding through all the different grits of sandpaper was for anal-retentive chumps. “Nonsense,” I thought, “I’ll just use some 60 grit to get out the larger defects, and then some 220 to smooth things out.” As it turned out, I was the chump.
Differing grits of sandpaper are meant to save you time, not waste it. If you’re just starting out, and you’re put off by the apparent large price of all those different grits of sandpaper, I’d highly recommend buying a variety pack that has a few sheets of each grit included. Then you’ll realize, especially if you value your time, that getting the right sandpaper definitely isn’t too expensive: it’s well worth it.
Basically, you are putting successively smaller and smaller scratches in the wood until, ultimately, the scratches become so small that they are “invisible” to the naked eye. So when you make coarse scratches in a wood surface—say, for instance, 60 or 80 grit—the fastest way to remove those scratches is with a medium grit: too large a grit (only slightly finer than the paper in your previous step), and you’ll be adding needless work; but too fine a grit, and you could sand for hours and still not remove the deep scratches.
Insufficient or poor sanding is a classic mistake common to a lot of beginning woodworkers. The wood is either given a quick, insufficient sanding; or else, if it is sanded to a finer grit, it is done haphazardly, and while skipping grits. The resulting surface my feel smooth to the touch, and may even look good from a distance with casual examination, but the proof is in the pudding, as they say.
Once a finish (and especially if a stain is applied) the sanding scratches will become all that much more noticeable and pronounced. You want to fix sanding mistakes before they’re embedded (and accented) under a few thousandths of an inch of wood finish / resins.
Learn how to inspect your sanding job between each grit
It’s not enough to just feel the wood or take a casual look and think “that’s probably good enough.” Sure, pros can sometimes get away with this lackadaisical approach because they have years of experience. But when you’re first starting out, anything that possibly can go wrong probably will go wrong: and nowhere is this more apparent than in the sanding.
Nothing’s worse than going through all the grits only to find that you still have some 60 grit scratches left in the wood from the very first step. To check, wipe all the sanding dust from the surface of the wood—I like to use a microfiber towel that can “grab” the dust right out of the pores and scratches of the wood. A can of compressed air or an air compressor can also blow the dust out, but it also creates a cloud of dust in the air. Once the dust is out, hold the piece up to a light (or bring a light to the workpiece if it’s something larger), and view the surface at a very low angle—almost parallel with the surface—to try and spot any serious/errant scratches.
Use alternating sanding techniques to find where (and at what grit) you’re having problems
While it’s not always the best (or most efficient) method in all circumstances, using varying sanding techniques can be invaluable if it seems like you’re running into repetitive sanding flaws in your work, and you’re just not sure where they’re coming from. For example you could sand the first grit by hand, parallel to the wood grain, and then the second grit could be with a random orbit sander, and so forth. Just take care that sanding directly perpendicular to the grain by hand puts some serious scratches in the wood that will be very hard to get out with a finer grit—a better solution would be to sand at a slight left-hand or right-hand angle from the grain, and not to cut directly across the grain.
The success in using this trick is rooted in the simple premise that you should hopefully know the direction and shape of the scratches that you’re putting in the wood. Sanding by hand with a stiff backing block? You should see deep, straight scratches. Sanding with random orbit sander? You should see little tiny circular squiggles all over the surface. Sanding with a pneumatic/rotary sander? You should see broad, circular/arc patterns in the wood. By changing the pattern with each successive step, you’ll be able to tell by the direction and shape of the scratches where you went wrong. When you finish sanding and find a flaw, you’ll be able to say something like this: “Okay, I see there’s still some swirl marks in the wood, which are 100 grit scratches made with my random orbit; I followed that up with some 180 grit hand sanding that apparently didn’t get all of the previous sandpaper’s scratches out. I need to spend more time at 180 grit to ensure I remove all the 100 grit scratches.”
2. Using incompatible products
Oily woods cause problems.
Steel wool can cause problems. (Use bronze wool instead.)
Oli and water don’t mix
Solution: shellac sticks to everything, covers a multitude of sins.
3. Not enough coats
4. No rubbing out
Whether gloss or satin, it’s an important step for all film-building finishes. It’s the answer to the comment that a thick finish looks plasticky.
Bonus mistake: no pore filler used.