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Topic: Any thoughts on a refinishing issue? |
Dan Beller-McKenna
From:
Durham, New Hampshire, USA
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Posted 14 Dec 2015 2:30 pm |
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I am having a local guitar restorer refinish the front of a Sho-Bud 6139. He contacted me today somewhat apologetically; seems to have run into an issue with the replacement zig-zag inlay that I provided him (same one used by current builders (at least Williams).
Anyone have experience with this issue that I could pass along to him?
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| "The reason this job is taking so long is that the bindings do not sand down evenly. The entire flat surface was sanded with the new binding installed to make it a flat plane. The thing is, the bindings are made of two different types of wood. There is the zig-zag white part and the black background part which is evidently softer. So even using a flat sanding block, more of the black wood is removed than the white wood. You can’t see this until you spray the lacquer on, and then the glossiness of the lacquer makes the indentations visible. I have been drop-filling the little dents individually with clear lacquer and a fine brush before spraying each coat. (Lacquer doesn’t flow into low spots – it just stays where it lands.)" |
Thanks,
Dan |
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Ian Worley
From:
Sacramento, CA
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Posted 14 Dec 2015 4:37 pm
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It sounds like he's already started lacquering, so not much you can do except extra coats of high-solids sanding sealer to fill it sufficiently. It's important not to rush through this, as lacquer, especially when applied in multiple/heavy coats, will continue to shrink for quite a while as a lot of solvent remains trapped under the surface. Take your time. With lacquer, you can't get a flat finished surface over an uneven substrate if you don't. Well cured sanding sealer will sand flat.
When faced with this sort of issue it's better to use a cabinet scraper instead of sandpaper on the bare wood. It's just a flat piece of steel with a burnished edge, works essentially like a straight razor. Standard practice before the days of sandpaper and power sanders, but alas, many such arts and skills are just disappearing.  It will leave the different woods flat and as smooth as a baby's butt.  |
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Michael Edelman
From:
Michigan, USA
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Posted 14 Dec 2015 5:57 pm
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That's what a luthier friend taught me. You don't use sandpaper on a violin  |
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Chris Reesor
From:
British Columbia, Canada
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Posted 14 Dec 2015 5:57 pm refinish issues
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I agree 100% with Mr. Worley's response.I'd just pass it on to the refinisher verbatim.
A cabinet scraper would leave the inlay level and require minimal sanding, probably only 220 grit or even finer, before finish is applied.
I use sandpaper to level shell and copper or silver inlays, with a small plexiglass block; anything made of wood or plastic, and out comes the scraper. Even figured woods can come out rippled if one tries to sand them flat.
I can't imagine how I would to do any kind of serious lutherie without a selection of scrapers.
cheers, Chris
_________________
Excel Superb U12, MIJ Squier tele, modified Deluxe Reverb RI, Cube 80XL, self built acoustics & mandolins |
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Carl Mesrobian
From:
Salem, Massachusetts, USA
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Posted 14 Dec 2015 7:07 pm Leveling
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For a natural finished piece, sealer or lacquer is the first coat on the piece. Then build up the topcoats - 5 or more is pretty typical among the builders I know. Each coat seems to show more defects as the finish builds (sort of the reverse of all the rocks you find when gardening)- after 5 coats ( 1 hour between coats) applied in one day, wait a couple days before leveling with 500. then shoot another coat, wait AT LEAST 2 weeks (I wait a month), block with 800 or finer, and buff. This is for something that has been prepped correctly to begin with. That's it
EDIT - One can also use a single edge razor with the ends taped leaving only the center blade exposed to level the high spots of lacquer. But, again, the lacquer has to be cured, or the dips will show as the lacquer shrinks. There are burn in sticks available for filling, but I usually make my own very sticky thick lacquer to fill pin holes, etc. Saves repeated applications of thin lacquer..
_________________
--carl
"The better it gets, the fewer of us know it." Ray Brown |
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Ian Worley
From:
Sacramento, CA
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Posted 14 Dec 2015 8:41 pm
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Just to add to what Carl said (as what you're dealing with is slightly different), finish lacquer is meant to flow and provide smooth finish. It doesn't build up quickly and does not sand well. When you need to fill and level a surface (however microscopic it may be) a high-solids sanding sealer is the best material to apply.
The nice thing about working with lacquer is that each coat "melts" into the one below. Coats bond to one another very well. You can apply coats of sanding sealer over gloss finish lacquer and it will work fine. You just can't apply too much without allowing some curing time. So... patience is the best advice here. |
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Carl Mesrobian
From:
Salem, Massachusetts, USA
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Posted 16 Dec 2015 1:15 pm
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But I don't recommend sanding sealer as a final topcoat; I am not a chemist, but if I recall conversations with chemists at companies that make the finishes, the sealers have additives (stearates) to build fast AND make for easier sanding.I have never seen sealer used as a topcoat - too soft. Lacquer is not hard to sand - it's a harder material than sealer. Let it dry and use stearate coated abrasives (whiteish in color). The coarsest on the first few coats would be around 500. If you are not getting a fine powder dust, you need to wait before sanding.
Also, if you have adhesion problems with the coats, you might need to either add a retarder (butyl acetate or butyl cellosolve) to the topcoat or mist the item with such before shooting the next coat. There's more to this than people think 
You might want to read this before going crazy with too much sanding sealer. I don't even use the stuff, except for millwork around the house
http://www.rockler.com/how-to/when-to-use-sanding-sealer/
_________________
--carl
"The better it gets, the fewer of us know it." Ray Brown |
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Dan Beller-McKenna
From:
Durham, New Hampshire, USA
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Posted 16 Dec 2015 1:21 pm
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| Thanks for all the thoughts folks. I think I will let this guy finish up the job as best he can, as it would seem too late to do it the right way at this point, since there are already several coats of lacquer on there. |
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Ian Worley
From:
Sacramento, CA
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Posted 16 Dec 2015 2:12 pm
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| Carl Mesrobian wrote: |
| But I don't recommend sanding sealer as a final topcoat... |
I'm not sure why you inferred that from my post, but that's not at all what I was suggesting. Sanding sealer is a base coat, and not intended to be a top coat. To clarify the point I was making, it is simply that clear gloss lacquer does not build well, does not sand well until well cured, and multiple coats can trap a lot of solvent, slowing cure time dramatically. No disrespect intended, but I too have had a wee bit of experience with this stuff over the years.
Sanding sealer is meant to fill irregularities and to deal with issues similar to the one under discussion here. Most of it gets sanded away except in the low spots that Dan's guy is dealing with. It can help mitigate a multitude of prior sins and ultimately provide a much flatter finished surface upon which to apply the actual finish coats.
Anyway, best of luck Dan. Just ask him to take his time and I'm sure it will turn out fine. |
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Dennis Saydak
From:
Manitoba, Canada
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Posted 17 Dec 2015 2:11 pm
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Personally, I'd just leave well enough alone but apply many extra coats of lacquer (probably 6 or  . Allow them to dry/harden a minimum of 30 days after the last coat and then wet sand the lacquer flat. It should end up perfectly flat with no noticeable waves in the inlays.
_________________
Dennis
Just when you think you're getting ahead in the rat race, the rats get faster. |
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Ron Pruter
From:
Arizona, USA
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Posted 17 Dec 2015 7:11 pm
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The last part of your finishers statement about not flowing into the low spots, sounds to me like trying to paint over a silicone polished area. The finish wouldn't flow. This causes something called FISH EYE. This is seen in the auto paint business a lot. To make the lacquer flow into the low spots you'll have to get a small amount of a product called fisheye flow out. It just takes a drop of this stuff in a shot glass of lacquer and the silicone doesn't reject it. Sounds like a chemical issue rather than a sander v. scraper issue. RP
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Emmons SKH Le Grande, '73 Fender P/J bass, Tick tack bass, Regal high strung, USA Nashville 112. |
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Chris Sattler
From:
Hunter Valley, Australia
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Posted 18 Dec 2015 11:09 am
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Upon reading the opening post what jumped immediately into my mind was "cabinet scraper".
I'm glad to other people think the same way.
Chalk another one up to the Luddites. |
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