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  #1  
Old 08-14-2020, 01:30 AM
nchin241 nchin241 is offline
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Default Poly to Lacquer refinish project????

Hi all,

Lots of shops and luthiers have refused this job and also talked me out of this, but with a dirth of free time on my hands and nothing else to do, I'm considering taking on a refinish project of an acoustic finished in poly and would like to respray it with nitrocellulose.

Does anyone have experience or tips on this? Let me know what I'm up against here...

If I decide to take it on I'll surely have some photos and step by step for everyone to follow along.
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  #2  
Old 08-14-2020, 01:50 AM
Big-E Big-E is online now
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I had my Yamaha FG365s top refinished in poly about 20 years ago. The "new" poly ended up cracking all over after about 10 years so I decided to have a go at removing it and doing a Tru-Oil finish. It was one heck of a job especially round the bindings and rossette with the poly melting into a gluey mess no matter what thinners I used (it wouldn't sand flat)! In hindsight, I made some fundamental errors which means I'll have to re-do it at some point in the future. However, the Tru-Oil finish was just what I wanted. It is a very time consuming job in my experience.
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  #3  
Old 08-14-2020, 07:19 AM
PeteD PeteD is offline
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I did this once on an inexpensive classical guitar that I had bought. I really liked the guitar and the tone was good, but it felt like the guitar was being strangled under the thick poly on the Cedar top. I didn't really care if I screwed it up and it was more of an experiment for me and an opportunity to build skills with refinishing.

Here were my learning points:

-It's pretty labor intensive to get that poly off and a nasty job for sure
-You should REALLY consider removing and reinstalling the bridge because no matter how hard I tried, I could not get all of the poly removed at the seams of the bridge/soundboard connection.
-Similarly I was not able to get all of the poly removed along the seams at the fretboard extension and I ended up marring the finish along the sides of the fretboard, which then needed to be blended in with the rest of the fretboard up the neck (which looked like crap)
-There was color change in the top since there was stain perhaps built into the poly and the cedar ended up looking blotchy after I re-finished it.
-You also have to note that there will not be a perfect blend on the edges between the sides and the top since part will be done with thick poly and the rest with thin nitro

The only way I would consider doing this again is if I could easily remove the neck and the bridge, and then I would strip and refinish the WHOLE body. That amount of time and effort is probably better spent selling the guitar and getting one for a little more dough which is finished in Nitro. For example, you can get into an Eastman easily for Yamaha money which is finished in nitro. Just one example.

My project guitar did have an improved tone, but there were so many noticeable visual issues that I ended up giving it away to a beginner who couldn't afford to buy a guitar.

If you choose to move forward, good luck with the project!
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Old 08-14-2020, 08:25 AM
RoyBoy RoyBoy is offline
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There have been threads on this topic before. I'd advise you to google it and read all you can before you dive in. Also, you haven't provided sufficient info for people to give you good advice.

Have you sprayed nitro before? It's a toxic substance requiring a full mask with VOC rated cartridges. You can do serious and permanent damage to your lungs otherwise. Finishing also includes LOTs of steps of sanding, polishing etc. to achieve a gloss finish. Not for the faint of heart. Also, lots of mistakes are normal/expected until you've gained a lot of experience.

Do you have a spray rig? spraying a guitar without one will take a lot of cans of Reranch. The materials cost could exceed the value of the instrument.

Is the instrument solid top? If it's ply, you won't likely hear a difference. In general, a plywood instrument will not have the dynamic range, regardless of finish. You may hear little difference in tone.

What kind of poly is on it? If the finish is really thick, it's probably a polyester resin which is a monster to get off. Strippers are useless and serious abrasion is really your only option, with potentially disastrous results on plywood. Just accept it for what it is and move on. If it's a thinner polyurethane, you can likely get it stripped OK. The question being, how much improvement will you able to hear. With an inexpensive instrument it could be negligible.

Sorry if this was TMI, but I couldn't tell from our post what level your instrument is or what your skill set is. Good luck with your adventure!
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Old 08-14-2020, 10:36 AM
Big-E Big-E is online now
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[QUOTE=PeteD;6468101]
.......-Similarly I was not able to get all of the poly removed along the seams at the fretboard extension and I ended up marring the finish along the sides of the fretboard, which then needed to be blended in with the rest of the fretboard up the neck (which looked like crap)......

........The only way I would consider doing this again is if I could easily remove the neck and the bridge, and then I would strip and refinish the WHOLE body......




Yep, not removing the bridge was one of my fundamental errors...
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Old 08-14-2020, 12:18 PM
nchin241 nchin241 is offline
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Quote:
Originally Posted by RoyBoy View Post
There have been threads on this topic before. I'd advise you to google it and read all you can before you dive in. Also, you haven't provided sufficient info for people to give you good advice.

Have you sprayed nitro before? It's a toxic substance requiring a full mask with VOC rated cartridges. You can do serious and permanent damage to your lungs otherwise. Finishing also includes LOTs of steps of sanding, polishing etc. to achieve a gloss finish. Not for the faint of heart. Also, lots of mistakes are normal/expected until you've gained a lot of experience.

Do you have a spray rig? spraying a guitar without one will take a lot of cans of Reranch. The materials cost could exceed the value of the instrument.

Is the instrument solid top? If it's ply, you won't likely hear a difference. In general, a plywood instrument will not have the dynamic range, regardless of finish. You may hear little difference in tone.

What kind of poly is on it? If the finish is really thick, it's probably a polyester resin which is a monster to get off. Strippers are useless and serious abrasion is really your only option, with potentially disastrous results on plywood. Just accept it for what it is and move on. If it's a thinner polyurethane, you can likely get it stripped OK. The question being, how much improvement will you able to hear. With an inexpensive instrument it could be negligible.

Sorry if this was TMI, but I couldn't tell from our post what level your instrument is or what your skill set is. Good luck with your adventure!
I've had some experience respraying soldbody electrics, but nothing as intricate as an acoustic with binding.

No spray booth my experience has been with rattle cans. I was incredibly able to purchase a respirator mask in February right before covid hit (haven't been back in stock anywhere since). Essentially my process with those solid body electrics was roughly 7-8 coats of lacquer, 30 minutes between coats. 1 month to cure before sanding up to 5000 grit and then buffing out with polish using a drill pad.

The only thing I'm cautious of is stripping the poly (which seems quite thin as compared to some other catalyzed polys I've seen before). I've seen lots of folks trying to take that finish off with a heat gun, but I'm cautious of that since we're working with a thin spruce top. My original idea was to sand the finish down to bare wood, which might take a lifetime to do but it seems like the safest approach, although I'm not sure if doing this has potential to damage the binding or rosette.

The guitar in question is a solid top/back/sides 000 style guitar. The instrument itself holds some personal value to me since it was one of the first guitars I bought when I was 15.
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Old 08-14-2020, 08:12 PM
PeteD PeteD is offline
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If it holds personal value, just make sure to ask yourself several times if you are willing to screw it up...is it worth that risk?!

If I were to do it again, I would probably take a razor blade and put a piece of painters tape on one side and then slowly and meticulously scrape the finish off at the fretboard extension by placing the taped side of the blade against the fretboard and scrape outward a half inch or so. Once you are through the poly there, then resort to an orbital sander to try to hog off as much of the poly as you can before moving to a sanding block and moving with the grain.

The bridge should really be removed to make this a clean job. But if you are not up for that, then use the same razor blade approach for the squared parts of the bridge. You will have trouble on the curved part on the back...so just prepare to have some poly shadow lines there. Or...ask a repair shop to just remove the bridge and then have a much better way to sand the top down.

You also might want to consider a waterbased lacquer to brush the top instead of the nasty nitro from a can. Much better for the environment, your health, and easier to apply if you don't have a spray rig.

But just know that this all needs to be a labor of love...because there will be labor.
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  #8  
Old 08-14-2020, 08:32 PM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by nchin241 View Post
My original idea was to sand the finish down to bare wood, which might take a lifetime to do but it seems like the safest approach, although I'm not sure if doing this has potential to damage the binding or rosette.
I suggest a cabinet scraper to remove the finish. Then sandpaper to prepare for the application of the new finish.
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  #9  
Old 08-16-2020, 03:28 PM
Th'Axe Th'Axe is offline
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Default Charles Has Got It

As I poke my way gradually into the art of guitar luthiery, I have been stunned learning just how effective scrapers can be, as I experiment with the grind, sharpening, and various blades. Some of the best are improvised and purpose-built. How does the story go about the violin makers spending 60% of their time sharpening and 40% using the sharpened tool? Personally, I really enjoy using a sharp scraper. The great thing about this art is the regularity with which I find myself humbled
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