Common Sanding Mistakes

Sanding isn’t fundamentally difficult but its still easy to make mistakes. This is often due to carelessness, such as over sanding the edges of a table top, but can also be due to procedural screw-ups such as not using the right tool or type of sandpaper for the job. Or sanding against the grain. Laziness also plays a role. An example here is not changing the sandpaper when its clearly worn out. Whatever the reason, making mistakes is part of the sanding experience and the goal of any self-respecting woodworker should be to make these mistakes an infrequent experience.

Without further ado, here are what I consider to be the most common mistakes when sanding woodworking projects.

Using the wrong tool

It’s important to understand the pros and cons of different sanding machines so you use the most appropriate tool for the task at hand. Some examples: A belt sander is great for removing high spots on a glued-up panel but not so good for final sanding. A palm sander is a good all-around sanding tool but not necessarily the best choice for the initial coarse sanding. If there are lots of mill marks and other defects, a random orbital sander is usually a better option for the initial sanding. It’s also my go-to tool when sanding a joint where two boards meet at a right angle because it leaves fewer swirl marks than other tools.

Staying in one spot too long

Whether you’re sanding by hand or with a machine, you need to keep it moving. Otherwise, you’ll end up with an uneven surface that may not be visible until after the finish is applied. It’s all about getting into a rhythm and sticking with it. If there’s a particularly deep scratch or dent in the wood, a little extra sanding of the affected area can sometimes be justified but if the blemish is really severe, most drastic action will likely be required. For example, applying water to raise the grain and hence diminish the depth of the blemish. Or perhaps even a full scale sanding of the entire surface.

Rounding the edges of the board

Even if you keep a power sander moving, there’s a tendency to round over the edges of the board. Good if you want rounded edges, not so good otherwise. There are a few ways to prevent this rounding: 1) avoid sanding to the edge of the board (yes, easier said than done), 2) place a scrap board of equal thickness against the work piece to keep the sander level, 3) use a sanding block near the edges.

Sanding through the veneer

Sanding through the face veneer of plywood is really the end result of several other mistakes but I think it deserves its own special mention since it seems to be a fairly common problem. In my experience, it usually occurs when I’m leveling off an edging strip and the plywood gets over sanded in areas where the strip is ever so slightly below the surface of the plywood. The obvious solution here is to do a better job applying the edging but also to avoid the temptation to rock the sander when sanding near the edges.

Pressing down too hard

When using a power sander, there’s no need to apply excessive downward pressure because the weight of the tool is sufficient. Your job is to guide the tool and let it do the work. If you find yourself bearing down, then there’s a good chance it’s time to change the sandpaper. Or perhaps use a coarser grit.

Using the wrong sandpaper grit

If there’s a “secret” to sanding, it would be selecting the appropriate sequence of sandpaper grits to arrive at a smooth surface with the minimum amount of effort. In other words, going through the grits. If you use too coarse a grit at any point in the sanding sequence, it will leave deep scratches that require excessive sanding to remove. If too fine, you’ll waste lots of time sanding, and sanding, and sanding, before the existing mill marks are removed.

Using too coarse a grit on end grain

The end grain of a board is harder than the face or side grain.  So, if you start out sanding a board with 100 grit sandpaper, the scratches left behind on the end grain will be much harder to remove than those on the rest of the board. The solution here is to start out with a finer grit on the end grain, say 150 grit. This may require a little extra sanding to smooth out the end grain, but it will save you time overall. Another benefit of sanding end grain with finer grits is that will accept the stain the same as the face grain.

Not changing sandpaper often enough

It’s easy to get caught up in the sheer bliss of sanding and forget to change the sandpaper once it wears out. Or maybe you realize the sandpaper has lost its effectiveness, but you’re too lazy (or too cheap?) to change it.  Regardless of the reason, if you don’t change the sandpaper often enough, the sanding process takes longer than it should. And that’s time that could be spent doing other fun stuff – like scraping dried glue off your workbench. An easy way to determine if it’s time to change the sandpaper is to run your finger over the sandpaper — if you can feel a pronounced difference between the unused part and the used part, it’s time for the switcheroo.

Sanding against the grain

We’ve all heard the advice about never sanding against the grain. Well, that’s good advice — up to a point. There are actually circumstances when it’s ok to sand against the grain. Such as when you first start to sand a board and need to level the surface and remove the mill marks. Sanding against the grain will often remove stock faster than going with the grain. BUT, once this initial cleanup is completed, switch to sanding with the grain. If you encounter a situation where you can’t avoid sanding against the grain – like a joint where two pieces meet at a right angle, try using a random orbital sander with fine grit sandpaper.

Hand sanding without a sanding block

It’s tempting to pick up a piece of sandpaper and start sanding away without using a backing block. Unfortunately, this will often create an uneven surface due to differences in finger pressure and because the sandpaper does not lay perfectly flat against the wood surface. So, don’t get lazy — use a sanding block. Even a small chunk of a 2″ x 4″ will work. For sanding irregular surfaces, a large rubber eraser works well as a sanding block that “forgives”.

Not removing sanding dust

If you don’t remove the sanding dust periodically, it not only partially obscures the surface but can also clog the sandpaper. And messes up the finish. And gets in your nostrils and eyes. And gets all over the place. So turn on your shop air filter, hook up the sander to the vacuum, use a downdraft table, do whatever it takes to keep the sanding dust under control.