Four Common Finishing Mistakes (and how to avoid them)

by Eric Meier

1. Not enough sanding

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.

Can you spot the cross-grain sanding scratches? I see this every night because this is my own nightstand made 10+ years ago.

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 pigments, dyes, and 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 work-piece 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 sander; 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 tropical hardwoods can cause a lot of problems; essentially, the finish seems to stay wet and tacky indefinitely. This is due to the antioxidants present in the heartwood, which prevent the finish from properly curing (through oxidation). This article explains the problem as well as possible solutions in more detail.

Even if you are using a finish-friendly wood species, you may still have trouble when using a combination of two or more products that are incompatible with each other. In short, oil and water don’t mix! Try to use finish products that all use the same base solvent. If you absolutely must use some specialty product somewhere in the finishing process, a good rule of thumb is to try to use shellac as a peacemaker between two incompatible coats. The adage goes “shellac sticks to everything, and everything sticks to shellac.”

Lastly, in rare instances, steel wool can cause problems when used under water based finishes. Namely, the tiny particles of steel will rust when in contact with water. (Use bronze wool instead.)

3. Not enough coats of finish

Most people are looking for the fastest, easiest wood finish. This is a perfectly understandable impulse, but if you’ve put all that work into a project, it makes sense to finish strong.

The temptation is to only apply one coat and call it good enough. However, the quality and protection of most film building finishes (such as polyurethane, lacquer, and shellac) goes up exponentially on the first few coats (e.g., there’s a huge improvement in durability and moisture excluding effectiveness from coat #1 to coat #2, and another big jump from coat #2 up to coat #3.) After maybe 3-4 coats, the benefits of increasing film thickness diminish somewhat. See this article on wood finishes for more info on what finishes work best in certain situations.

One last tip that will increase the clarity of your wood finishes: when building up wood finish film thickness, use a glossy finish. Even if you want your final sheen to be satin or low-gloss, I recommend using high gloss on the initial coats whenever possible. This is because most satin finishes contain a flattening agent that dulls the surface of the finish, and can appear cloudy when built up in several layers. Instead, simply rub out your final finish layer (see tip #4) or apply a satin or low-gloss finish as the final coat of your finish.

4. No rubbing out

Most of the time, when advocates of only using a single thin finish film complain that thicker finishes look “plasticky,” it is usually because the finish was slopped on in several thick, drippy, gobbledy-gook coats (polyurethane is chief in this trespass). I would agree, such finishes do look like cheap plastic, but that isn’t solely due to the number of coats of the finish, but simply that the number of errors, defects, and unevenness in each coat accumulated without correction until you are left with one thick, bumpy, coat of clear plastic.

Consider this: many guitars are finished with ten or more coats of spray lacquer. Most of us would not say that the mirror-polish on guitars is plasticky at all. What’s the difference? After all those coats, the guitar’s finish was sanded level and then rubbed out.

The art of rubbing out is perhaps too long to go into detail in an overview article like this. In a nutshell, a sufficiently thick film is applied to the wood surface and allowed to thoroughly harden over several weeks. Then, the finish is sanded flat and level (the thickness of the finish helps create a buffer so that the sandpaper will not actually cut through down to bare wood during this process).

Next, with a perfectly flat and uniform surface, the finish can be buffed up to whatever sheen is desired for the piece. (One additional mistake that can sometimes get overlooked is when no pore filler used, which means that on many porous woods, even with ten or more coats of finish, the pores still leave an uneven surface after leveling.)

Honduran rosewood psaltery back rubbed out with #0000 steel wool
Psaltery back rubbed out with #0000 steel wool and then polished to a high sheen

For most beginning woodworkers, an easy way to get familiar with the process of rubbing out is to simply apply a few extra coats of wood finish to your project, and then sand it lightly with 400 grit sandpaper to remove all surface dust and irregularities. Then use #0000 very fine steel wool and rub the entire surface of the piece, this will leave a very pleasant and uniform satin finish that softly diffuses light.

Are you an aspiring wood nerd?

The poster, Worldwide Woods, Ranked by Hardness, should be required reading for anyone enrolled in the school of wood nerdery. I have amassed over 500 wood species on a single poster, arranged into eight major geographic regions, with each wood sorted and ranked according to its Janka hardness. Each wood has been meticulously documented and photographed, listed with its Janka hardness value (in lbf) and geographic and global hardness rankings. Consider this: the venerable Red Oak (Quercus rubra) sits at only #33 in North America and #278 worldwide for hardness! Aspiring wood nerds be advised: your syllabus may be calling for Worldwide Woods as part of your next assignment!

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Cathy

Hi – I’ve learned a lot from reading the questions and answers below. Thank you. My question – hand me down beautiful old varnished table from my parents. Not solid wood top. There was a crazy thick varnish finish that I’ve finally managed to strip and sand away – although it isn’t all one shade – I will use a solvent to be sure it’s thoroughly cleaned, and hopefully I’ve sanded it evenly enough. My question – I’ve made a few gouges into the veneer that I need to fill. I am planning on finishing the top with oil. With… Read more »

TJM

What a great blog, thank you for writing it! Ive been battling with a new oak floor (which had an awful plastic finish on it) making every mistake under the sun as the finish was impossible to get off. Even resorted to an angle grinder for sanding. . Ive now started again with a makita belt sander and am examining each board with the light shining across it, marking the mistakes. Plus hand sanding with the grain on patches. Starting with 24 grit on the belt sander to remove the new finish (osmo wood wax finish). Do i need to… Read more »

Emma

Just moved into a new house. Wood kitchen worktops not looked after so i bought a kit and sanded them down. After second coat of oil, I still have patches that look dry/flakey – see attached. Any recommendations:?

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Emma

Hoping this shows it better – where the wood looks scuffed/ white rather than brown.
I used Danish wood oil from a company I found on amazon??
Thanks

Emma

hopefully this one works – apologies

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Emma

Well its kind of both. Its those whiter patches on the wood you can see in the picture. when you look closer, the look is scuffed (as if its the sandpaper look still because its also not smooth to the touch AKA dry….). i dont really know how else to describe it…

Emma

Amazing thank you!

Mary

Hi there – will primer before painting hide swirl/pigtail marks left from sanding? If not, should I resend with a 220+? Thanks!

Laurie

Hi we recently had oak stair treads put in. My husband is staining them, first time. Our contractor said to sand with 220. After sanding and staining we noticed these marks, what can we do? Help!! Thanks!

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Lee White

the finish is like fish scales

Lee White

the wood came up like fish scales after i applied varnish

Lee White

ive sanded down twice and waited a full day ,with that i used a high gloss varathane , and when i look at it ,,see this is it the wood?

erik rider

Forgot to add the second pic. You can see it more on this one. Thanks for your help.

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erik rider

Hello! I am finishing a parota cookie and need someone to let me know if this is okay or not.

I have a festool orbital sander with every grit of sand paper.

I want to oil the piece at 220 grit but I’ve noticed that I’m getting shiny lines where I sand. I’m scared that if I put the finish on, that you will see it. I don’t have this problem with regular tables, only this end grain cookie.

My question is: is there something I’m doing wrong or will it disappear when I oil it.

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Emer

Hi, my husband took a belt sander & hand sander to a modern oak table & then applied 2 coats of Osmo polyx white tint oil. The result- so many sanding swirls with the paint from the tint making them more pronounced. I started again using a Mekita RO sander, working through good quality pads – 80,120 & 180, twice with each grit (using the pencil mark method to assess when to go up a grit). I worked slowly, following the line of grain & cleaning dust off between sanding. Took hours! The result is no better! Still lots of… Read more »

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Emer

Many thanks for your response. The wood is solid oak and when wiped with solvent, the swirls pop, as they did when oiled before I re-sanded again. The swirls seem to be from the belt sander as they weren’t there before that. I know they will pop again if I oil again now and am wondering how to get rid of them?

Daniel Campbell

Ur problem is definitely the belt sander it has dug into the timber. I can clearly see this as I’ve used a belt sander for years. Only way till try and fix this is go back with belt sander on a 80grit and work up till 120 with belt sander then till 220 by hand (with the grain). But u must sand with the grain and always keep the belt sander moving and don’t be tempted till put pressure on the sander let the machine do the work, if u apply pressure u will end up with the very same… Read more »

Emer

Very many thanks Eric and Daniel for your replies and suggestions. So kind of you to take the time. In the end, I asked a friend whose a carpenter to do it and now it’s perfect! He used a large rotary sander with netting pads & and extractor. He worked through the grits and did a fabulous job.
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Amanda

I love the color of your tabletop!! What stain did you use? That’s what I was aiming for but I didn’t grab the right color

Emer

Hi Amanda, I used Osmo White Tint 3040. Hope it works well for you

Holly

Help needed! My kids used kinetic sand and made a ton of scratches in our beautiful kitchen table. I quickly tried Tibet almond oil and murphys oil and it only made deep water stains in the grain. My husband came home hours later and sanded away the scratches and oil stains and applied 2 layers of polyurethane. Then he did some more light sanding and put on another layer of polyurethane. Thought the problem was fixed. The table looked different but still good. However it has been almost a month and now we are seeing new darker spots and some… Read more »

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Nick

Hi, we just finished our floor and these white discolourations have appeared… help pls! what is it and how do we fix it?

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Kayla

If you skipped a few grits, say from 36 straight to 80, should you go back over it with a 60 grit ?

Malisa Thomas

I’m trying to strip my lacquered table In order to re-stain and finish. I think I’ve sanded too much! There’s soft spots (light/white) in some of the grain. I tried using a stripping agent which seemed unsuccessful. Now I’ve done the first layer of sanding with 100 grit paper. Will this sand out as I get finer paper? Or do I keep sanding till it’s all very light (I think it’s maple)? Or how can I fix this! Help!?

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Malisa Thomas

Ok. Thank you!

Maren

Hello, I wondered what to do about these shiny patches that appeared after I treated our oak kitchen top with Liberos Pure Tung Oil. Sanded it with electric sander and by hand right back to bare wood; then started to apply coats but have shiny patches in places. The wood has absorbed and is a matt finish in other places as I intended. I wondered if it is some build up resin from the drying process? Maybe I did not wipe off the excess oil enough after application? What can I do to get an even finish? Can I wipe… Read more »

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