unknown damage to Tru-Oil finish, please advise

Question

First, I'll show you a pic of the damage, then I'll give you a short background to how this happened, then last I'll ask for advice.

The damage:

As you can see there are tiny specs in the Tru-Oil finish (one single application) on my black walnut board.

Background info:

Here's what happened.

I'm making a shelf with these black walnut boards and I did a very good job with the sanding, started with 60 grit (very rough sawn from my friend's saw mill) then 80, 120, and finally 220.

Then, I had to abandon the project for about a week and they sat in my garage (where I also worked on getting a riding lawnmower started). Then sanded them with 320 grit before wiping on a single layer of Tru-Oil. They looked really really great the next day.

My next step was to apply spar-urethane over them to protect from UV and water, but unfortunitally I became pre-occupied with something else and they sat on the garage for some more time, during which it rained extremely hard and some leaks in my roof formed and dripped water onto the floor next to where the boards where laying. Then yesterday I discovered the damage.

So.. it was either caused by water splashing onto the boards and ruining the Tru-Oil (they say it's water resistant but not water proof). Or something like WD40 got onto the boards in-between finish sanding and applying the Tru-Oil and that caused it to react this way. Or... ?

The question:

Do you think this is water damage? The effect of WD40 or similar on the wood before the finish was applied? Something else? I think it's water damage but I just want to cover all bases, and I'm surprised that Tru-Oil would do this.

And what should I do? Sand it smooth and start over, or apply a new coat of oil on top? I know that there's a noticeable difference in darkness and sheen from 1 coat to 2 coats of Tru-oil. And if I sand it off and start over, what grit should I start with?

Thanks!

Answer 1

Thanks for the detailed background info, don't get that enough.

Do you think this is water damage?

It certainly looks like it but it's hard to tell. You can get much the same look from a dot of WD-40 so it's difficult to be sure. No need to panic either way as one of Tru-Oil's benefits is it's easily retouched/topped up.

First thing I would do is give it a wipe with mineral spirits and then let it dry. That alone may do quite a lot to reduce the visibility. Then rub in a very light coat of Tru-Oil, thinned if necessary with some MS. I'd be very surprised if that doesn't resolve the issue.

I think it's water damage but I just want to cover all bases, and I'm surprised that Tru-Oil would do this.

Tru-Oil just isn't that tough or resistant a finish, but to be fair to it in this case it's nowhere near being cured. Curing might take a fortnight or longer and it's only after a full cure that you can expect the full measure of protection from any finish.

And if I sand it off and start over, what grit should I start with?

I wouldn't recommend sanding this. I'm not a fan of sanding off finish anyway, as you'll see from previous Answers here if you have a poke around, but here because the Tru-Oil won't be hardened (it'll never get that hard BTW) it could be a bear to sand off due to clogging of the paper.

If you do find you have to remove it I'd use an organic solvent, starting with acetone if mineral spirits has no effect. Once you find the solvent that's strong enough after a surprisingly small amount of effort and not too much rubbing you'll get to something close to bare wood, without any risk of damaging the piece from sanding. Then wait for the wood to dry and you're ready to begin again.

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Completely unrelated to your question here I highly recommend getting friendly with hand planes and scrapers. All that talk of sanding from 60 grit made me itchy :-)

It's not just about personal preference, a hand-plane dude might generate about 1/2 teaspoon of dust at most taking a 72"x8" board down from rough-sawn to ready for finish, and possibly faster than via sanding too.