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Smoothing old finish

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Forum topic by Dave Rutan posted 12-04-2018 12:05 AM 453 views 0 times favorited 5 replies Add to Favorites Watch
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Dave Rutan

1775 posts in 2607 days


12-04-2018 12:05 AM

Topic tags/keywords: violin finish polyurethane smoothing repair

If the above image makes you queazy, pretend it’s a piece of pine veneer.

This old violin looks like someone in the distant past slapped a coat or two of something like polyurethane on it with a big old brush. Then it suffered water damage, or high humidity. It could be as simple as storage in an attic.

So I solved the hazing problem with a heat gun. It worked great. Now I want to know how I could possible smooth out the brush strokes without simply striiping the poly off. What would be the best way to do this?

Thanks for any thoughts.

P.S. The finish is immune to water, alcohol, and mineral spirits.

-- Ni faru ion el ligno!


5 replies so far

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Oldtool

2778 posts in 2609 days


#1 posted 12-04-2018 02:12 AM

Hard to determine whether or not that picture is before or after you solved the hazing problem, the right side looks like it still has moisture in the finish.

My opinion, for what it’s worth, would be to lightly sand the entire instrument with very fine paper, maybe 500 grit, until the entire body is a consistent color, then stain if desired and finish with a product of choice.

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

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Dave Rutan

1775 posts in 2607 days


#2 posted 12-04-2018 02:21 AM

I took the picture when it was still 1/2 and half. It’s now a pretty consistant hue, with brush strokes.

Do you think it’s possible that I could lightly sand the poly till the brush strokes are at least hardly noticeable and then maybe go over the instrument with some kind of oil? I’ve heard some luthiers use the old reliable BLO. The idea is to not refinish the instrument, but rather make it look acceptable for sale.

I think this instrument is more of a challenge than the one with the fractured face that I’m putting back together.


Hard to determine whether or not that picture is before or after you solved the hazing problem, the right side looks like it still has moisture in the finish.

My opinion, for what it s worth, would be to lightly sand the entire instrument with very fine paper, maybe 500 grit, until the entire body is a consistent color, then stain if desired and finish with a product of choice.

- Oldtool


-- Ni faru ion el ligno!

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WoodenDreams

619 posts in 329 days


#3 posted 12-04-2018 06:35 AM

light sanding with eventually smooth out the brush strokes. I’d try 220grit first, then switch to higher grits as you get closer to smoothing out the brush strokes. With the thickness of the wood I’d be careful with the wood. After restoring this, you should have a nice looking instrument.

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Oldtool

2778 posts in 2609 days


#4 posted 12-04-2018 01:05 PM

I’m not a finishing expert, but from what I’ve read, oil won’t penetrate through the poly, so doing this might yield two tones – areas with and without poly on the surface.

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

View Dave Rutan's profile

Dave Rutan

1775 posts in 2607 days


#5 posted 12-04-2018 01:23 PM

I guess I could test that with a wipedown before deciding. I’m concerned that my lite sanding will leave a very dull finish.


I m not a finishing expert, but from what I ve read, oil won t penetrate through the poly, so doing this might yield two tones – areas with and without poly on the surface.

- Oldtool


-- Ni faru ion el ligno!

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