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I built this table out of ash, and finished it with Osmo Polyx hardwax oil, about 2 years ago. Recently a brown stain about 1/2" circle appeared. It looked to be down deep in the wood. The Osmo oil finish still repels water, but I figured perhaps it had gotten thin there and allowed a spill to seep in. I read online that you should sand down and sometimes that can remove it, but if not, to treat it with mineral spirits. Mineral spirits are banned in California now, but I read that acetone can also work.

So...I sanded down, which did nothing, then wiped with acetone, which also did nothing. I brushed off the sawdust but didn't vacuum (I suspect that was part of my mistake here). I then coated with some Osmo Polyx, figuring that might darken the sanded spot. No luck.

As you can see, it pretty much looks terrible in that spot. Is there anything I can do to mask the sanded spot at this point? Maybe a wax filler stick? Or sand again deeper and then vacuum well? I just want to get it back to the original wood color at this point. Medium-zoom picture of wood tabletop with a damaged spot that was sanded over Closeup-zoom picture of wood tabletop with a damaged spot that was sanded over Overall image of table

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    This is one reason I'm a vocal critic of the "you can just sand a spot and locally refinish" thing that so many products now tout. Yeah, you can, but if you've sanded much the colour ain't gonna match because the sanding will have changed the colour of the wood! You have any scrap ash from the same project? If it's been shielded from light compare to the underside of the tabletop, if it has had a good amount of light exposure in the scraps pile, just sand it well and be amazed at how pale freshly worked ash can be! (The stuff I harvest locally, the sapwood is very nearly white.)
    – Graphus
    Commented Oct 24, 2023 at 7:38
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    BTW in case I don't get to say it in an Answer, best not to think of acetone as a substitute for mineral spirits basically in any scenario. They are both organic solvents but that's about as far as the resemblance goes :-) Not that I think it should be banned, but by all rights acetone shouldn't be available in Cali any more either but it has special status in the whole "VOCs are gonna destroy the world" hysteria, despite being 100% VOC!! <sigh>
    – Graphus
    Commented Oct 24, 2023 at 7:50
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    BTW do you have a best guess about what the stain might have been caused by? Red wine? A table sauce?
    – Graphus
    Commented Oct 24, 2023 at 7:53
  • @Graphus Thanks for the info. I agree 100%, having gone through this experience, that "sanding to repair" is not a good solution, because of the color change issue. Great point about acetone also. The stuff evaporates in seconds and I'm sure it's not great to breathe so why is one banned but not the other? It's a little silly. Great question about what caused it. I'm really stumped. What liquids could permeate an oil finish? There was a pumpkin sitting in that spot when we noticed it so my wife thinks the pumpkin did it. (It sounds like a horror movie title, ha!) Commented Oct 24, 2023 at 14:08
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    Here's a video from a guy I like on YouTube. He compares the stain resistance of about a dozen different hard wax oil finishes. It's one of a multitude out there making such comparisons and happens to be the most recent I've watched. At some point, it would be interesting to compare all the comparison videos to see if they come to the same conclusions...
    – FreeMan
    Commented Oct 24, 2023 at 21:51

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Is there anything I can do to mask the sanded spot at this point?

Possibly.

Despite the much-touted potential with some finishes to be able to "just sand and reapply the finish and the repair will be unnoticeable" the reality is often found to be different!1

The main issue with localised work on the surface of wood (finish or no finish) is: fresh wood is not the same colour as wood that has been exposed to light for a year or more.

We're often not consciously aware of this natural darkening because of course it happens incrementally over a long period, but as soon as you attempt a spot repair one becomes acutely aware of it! When you sand more than the lightest amount you are sure to reveal the fresh colour of the wood as has happened here. (Same if you have to plane or scrape.)

In theory you could therefore adopt a wait-and-see attitude and, fingers crossed, in six months or more the wood at the repair spot will have darkened to the same colour as the wood around it. That's a long time to wait with only a chance it'll come out good in the end.

Some refinishing guides suggest local dyeing of paler repairs to match the colour of the wood around them. But while this certainly can work for the short term, what about when the wood beneath naturally darkens? IMB this approach might be fine for certain low-visibility areas, especially on surfaces that don't get a lot of direct light, but the middle of a tabletop.....?

This is right in the middle of the most visible surface of a table, and like all such defects it will naturally tend to draw the eye. Worse when you already know it's there!

So I think that unfortunately the way to go is to just swallow the effort involved and refinish the whole top. That's what you'll have to do anyway should the spot-refinishing attempt not work out long term.

If you go ahead with a full refinish you can take the opportunity to fully sand or heavily scrape the top and that might get down low enough that it'll erase the dark spot. It's sure to lighten it substantially at least. I would be inclined to try to get rid of the spot first2 myself, but that's totally up to you.


1 In fact that quote might be better expressed as "just sand and reapply the finish and if you're really really lucky the repair will be unnoticeable" ^_^

2 Since the stain could be of vegetable origin there's a decent chance the dark spot can be successfully lightened using common household bleach. If that doesn't work an oxalic acid solution would be the next thing to try (often works where conventional bleaching has failed, on red wine stains for instance).

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    Really interesting point about the possibility of vegetable origin. I'm going to try to bleach, and if necessary the oxalic acid, and see what happens. Thank you for the helpful info! Commented Oct 25, 2023 at 4:55
  • You're very welcome, glad to try to help.
    – Graphus
    Commented Oct 25, 2023 at 7:30
  • @FreeMan, the system is flagging all the many responses under the OP's post and wants to move the discussion to chat. So I'll cheat and respond here tee hee. "Honestly, the test methods are all quite varied and I know that does make it difficult..." So so difficult to try to draw any firm parallels. One of the most recent comparisons I saw (Lincoln Street?) the host mentions letting all his (many!) finish samples cure for multiple months, which is definitely something that not all testers do as you know.
    – Graphus
    Commented Oct 25, 2023 at 7:59
  • @FreeMan, BTW if you ever want to do your own shootout, here's what I would do with the liquids that nobody (I've seen) does: leave them on until they're dry. THAT'S an acid test of finish protection, not 30 minutes or an hour. [Not every varnish or lacquer will pass this so for sure hardwax oils will fail spectacularly as a rule.] I think every parent has at some point discovered a stain dried on the surface of a table or counter and it's that kind of worst case that IMO should be tested for, not whether the wax component can 'hold out' for 30-60 minutes (even some paste waxes can do that).
    – Graphus
    Commented Oct 25, 2023 at 8:06

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