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| Touching up varnish damage http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=47824 |
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| Author: | MaxBishop [ Fri May 27, 2016 8:23 am ] |
| Post subject: | Touching up varnish damage |
I was recently replacing the fretboard on a guitar that I had made some time back. The finish on the top on either side of the fretboard had been damaged and in some places it was down to bare wood. Originally I had finished the top by sealing with shellac and applying 3-4 coats of spar varnish (Petit Z-Spar Captain's Varnish). I'd rather not try to refinish the entire top because I'll have to remove and replace the bridge and golpeador (it's a flamenco guitar). Anyone have any tips or tricks about a partial refinish with varnish? Thanks, Max |
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| Author: | jfmckenna [ Fri May 27, 2016 9:42 am ] |
| Post subject: | Re: Touching up varnish damage |
I can't speak from experience since I literally just started using varnish and completed my first guitar with it a couple weeks ago but... I sanded through the VERY thin finish in a couple spots and here is what I did. I thinned out some varnish and dipped a cotton rag in it and then wiped the rag on a scrap piece till all the heavy flow came out of it and then just very quickly swiped over the sand through just once. Then let it dry for a day and repeat till it's done. It almost looks perfect as is but I will wet sand touch it up and buff it out in a few days. The varnish I am using is a Sherwin Williams fast dry oil varnish so take my experience with a grain of salt. But I have found it to be very very forgiving. BTW I have used shellac in the same manor and for similar situations if it's just a minimal touch up like around fret ends for example. |
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| Author: | Barry Daniels [ Fri May 27, 2016 10:08 am ] |
| Post subject: | Re: Touching up varnish damage |
Varnish does not burn into itself so you may have witness lines, but it can be touched up or drop filled like lacquer. |
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| Author: | Pat Foster [ Fri May 27, 2016 11:41 am ] |
| Post subject: | Re: Touching up varnish damage |
On oil varnish that hasn't aged too much, a dose of acetone in the touch-up varnish can help with burn-in. Power buffing can help too. Don't know how you could test in your situation, though. Standard disclaimer: YMMV. Pat |
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| Author: | B. Howard [ Sat May 28, 2016 7:28 am ] |
| Post subject: | Re: Touching up varnish damage |
Blending in finish repairs on finishes that do not reactivate or "burn together" can be a challenge. But in most cases witness lines can be greatly reduced and even eliminated. It starts with the prep of the area. You must prep an area much larger than the repair itself so you have room to thin the coating towards the edges. Prep the area by thoroughly cleaning with some DA or naptha ( DA removes grease and silicones a bit better but eats some types of finish....). Scuff with some 400-600 grit paper or maroon scotch-brite. Make sure to break the surface and de-gloss the surface well. In a situation like yours Max i would prep everything from mid sound hole up. Clean off the dust but do not use any solvents. Apply 2-3 coats over any bare or really thin spots with good dry times between. once this is dry a bit of level sanding may be required on the new material. Now thin the finish about 15% with the correct solvent and apply a coat that covers the repair and a bit more of the prepped area. Repaet adding thinner and slowly making the repair spot larger covering more of your prep area. ab out the time you hit 60% thinner you should be right out to the edge of where you prepped. Allow plenty of time to dry, the extra solvent will take time to work out of the film. Now simply level sand and buff out as normal and you should have a repair that looks very good and is hardly noticeable. |
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| Author: | MaxBishop [ Sat May 28, 2016 9:06 am ] |
| Post subject: | Re: Touching up varnish damage |
Here's a picture of the damage. Attachment: #25 damage.JPG Max |
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| Author: | Barry Daniels [ Sat May 28, 2016 11:09 am ] |
| Post subject: | Re: Touching up varnish damage |
Those blisters need to completely removed down to the wood surface. But I would recommend a complete refinish of the top. It won't be much more work than the repair, and is the only way to make a blemish free finish. Repaired finishes on spruce seldom turn out invisible. |
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| Author: | jfmckenna [ Sat May 28, 2016 12:22 pm ] |
| Post subject: | Re: Touching up varnish damage |
That's gonna be a tough one for sure. I think I would still try and repair it. If anything you will get some experience repairing the type of finish you use. |
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| Author: | truckjohn [ Sat May 28, 2016 12:56 pm ] |
| Post subject: | Re: Touching up varnish damage |
It will be less obvious once the fretboard is on. The fretboard will provide a natural contrast and edge that will reduce how obvious it is. I would just go ahead and refinish with the same schedule you used for finishing and hope for the best. The witness lines will be reduced when you polish it out. |
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| Author: | MaxBishop [ Sun May 29, 2016 6:59 am ] |
| Post subject: | Re: Touching up varnish damage |
Many thanks to all for your advice. I will try to remember to post photos if I get notable results. Max |
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