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I'm doing my very first French polish finish on a little Size 5 guitar, and I've run into a problem. In trying to fill some pores with pumice, I managed to create this little 1" by 1/2" crater-like area. I have four coats of shellac on the guitar, so far. What is the best way to fix this area?

Any helpful suggestions would be greatly appreciated!

Kathy

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Yeah, that can happen if you concentrate on one spot too long. If this is your first attempt at FP, the easiest way forward would be to sand back the entire back to almost level, using about 800 grit, wet or with oil. Proceed normally from there.

Thanks, Greg! I was thinking that's what I might have to do. Are there any other ways to deal with this, or is this the safest? (I have Z-poxy pore-fill underneath the shellac.)

Also, what's the best way to deal with the stray pores, here and there, that weren't filled by the Z-poxy?

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Kathy, I just did my first French polish on a bass uke. I spent the money on O'briens online French polish class. Worth the money btw. He mentioned a couple of times about not going too thick with the shellac at one time because it could cause problems. Not sure if this is your problem, but that is my uneducated newbie guess. I will be watching closely to see what the more experience folks have to say. Good luck!

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Kyle

You can also spot fill by brushing on shellac and letting it dry for a day or so, and then leveling with a razor blade. However, going this route can easily lead to worse problems.

It is possible to get a perfectly flat glossy finish using FP technique alone, but it's not likely to happen on your first try. It will come naturally with experience. At least it did for me. Until then, all the basic lacquer leveling techniques work just fine with shellac. Do be careful not to sand through though. Better to only sand it partly flat for now. It will naturally start to level as you proceed.

FB requires quite a bit of subjective feel. I've spent at least a few hundred hours french polishing, and I still struggle with it if I haven't done it for a while. I think Frank Ford's quick explanation is about the best. It's really imperative to see that cloud. The Milburn tutorial is good but it almost has too much information.

Regarding stray pores, the nice thing about FP is that it will tend to fill these in as you continue. The pad tends to smoosh the shellac into them.

Kyle: Thanks! I think I have a handle on how to apply the shellac thinly and smoothly; I'm getting a "feel" for it. But my problem is in how to properly do the pumice pore-filling (in the midst of the bodying sessions); in my inexperience, I probably put too much pumice and/or alcohol on the pad.

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Yeah, I think I shouldn't try this, as I have never had great luck in making such spot-filling repairs unnoticeable. I could see myself making it much worse. I think I will go with your suggestion of sanding it down to near-level with 800-grit and oil.



Yes, the only part about sanding it flat that makes me nervous is the possibility of going through the Z-poxy coats underneath! I guess I just need to use a very gentle hand.



Okay, then, I'll stay away from the pumice!

Thanks, Greg!

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

I think it depends on how many unfilled pores you have and how deep they are. The pumice method can be very tricky and IMO is actually much more difficult than the actual FP process. You could wet sand the entire Back and let it all dry. You can use the powdery residue to help fill the pores if they are shallow. I'm afraid the deep ones will need the same treatment numerous times, probably much quicker to fill them with Pumice or some other filler.

It is possible to fill stray pores with pumice after you've started, but it's a bit tricky and probably best avoided for now.


You're welcome! Glad to help.

EDIT: BTW, if you are going to do pumice filling after the bodying has begun, IMO the pumice should be mixed with shellac, not alcohol.

That area looks deep. How thick is the finish? The nice thing about FP is that it can go on very thin ans still be smooth. Are you pumicing with shellac or just alcohol? If you want to take the finish off without sanding through the epoxy you could take it of with alcohol and a rag. It will take some work but you wouldn't have to worry about sand through.

As you are doing the FP, when you notice problem areas, the best thing to do is to resist the urge to focus on the area. keep going without trying to concentrate on the spot and things tend to even out. I'm not very experienced with FP but my guess is you are using either too much shellac or it is not thinned enough. When I started getting better results, I was amazed by how little shellac you need on the pad. . .

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

If you pore fill with z poxy do you still have to pore fill with pumice? I pore filled completely with zpoxy and went from there with the FP. Just curious.

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Kyle

Kathy, I don't think you need to sand the entire back, I'd sand around the area and try to sort of feather it in, and keep polishing. You can always go at part or all of the surface with fine abrasives between build sessions. Purists will frown but so be it.

I don't see any problem with trying to fill stray pores in an epoxy fill with pumice. Pumice filling is definitely an acquired skill - I get spots like yours when I do it. It is probably not so much a crater as a gob of pumice accumulation around the area you were working?

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Jim Kirby
kirby@udel.edu

Michael: I don't have very many unfilled pores, actually -- just some shallow pores in small areas in a couple of sections. I think I might just let the further shellac coats fill them...to be safer. Thanks for the ideas.

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Bryan: I used both shellac & alcohol, so maybe it was just too much pumice and/or alcohol.
In the past (I think it was my baritone uke) I have removed shellac from a top with alcohol --- but wouldn't the alcohol go through Z-poxy, too?
Yes, that's very good advice. Thanks, Bryan!

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

I thought all the pores were filled, but didn't notice the unfilled ones till later....sigh....

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Jim: That might be another idea, sanding around it first. Thanks for the suggestion! And that might very well be what it was --- if so, I must have put too much pumice on the pad!

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

Thanks, all, for the tips and ideas and suggestions....This is all new to me, so it's been a real education (and I'm sure will continue to be)! I'm going to let it sit till at least tomorrow night, to let it harden up a bit before I attempt any sanding.... Will let you know how it ultimately goes.

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

I agree with Jim. If you have a crater like that, you probably have excessive build-up around it. Most likely gradual, but it only takes a catch to cause this problem. Sand it down with some wet n dry 400 or 600, using a block and NAPHTHA mixed with olive oil as a lubricant. Wipe it dry often and check where you are. May want to build a bit of FP in the area, after a bit of sanding, then sand again if the crater is still there. If you work it right, you won't be able to tell at all when you are done. I have faced this problem more than once.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Hi Kathy. I'd use a pounce bag (some pumice in a piece of cotton ... looks like a French Polish fad, but filled with pumice). just tap it on the area, spread it out a bit if too much gets on, then go over normally with your normal fad (maybe with a bit more oil than normal). At first it seems like a big mistake, but keep at it and it should smooth out in a session or two.

Waddy: Thanks for the tips. Why mix the naptha with the oil? Other things I've read just say to use oil. What does the naptha do?

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

David: I think I'll need to do some practicing on scrap! Thanks.

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

It looks to me like the "crater" is in the epoxy, not the FP. If you apply FP over epoxy too soon it will absorb the solvent and swell, except in areas where you have sanded through the epoxy (or washed it off with the solvent) where there is nothing to swell, so you see the crater. I think you'd see any attempted "fill" using FP/pumice etc. because I think you have a lack of epoxy beneath and my guess is that it will ultimately show (to you at least!).

So, before you have too much time invested in the FP, I'd be washing it off with DNA, letting it dry well and then re-doing the epoxy fill (just on the back, unless you have issues on the sides as well). Give the epoxy at least 24 hours to cure before hitting it with a solvent and start very dry when you apply the FP. If the epoxy is a continuous thin film you have to be careful not to locally remove parts of it.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor's thoughts begs the question as to whether you sanded back to wood before starting the shellac process, and how long you waited before starting to FP? Is this crater in the area where you were trying to fill the pores with pumice? That's what I'd do if I noticed unfilled pores after I started polishing.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Kathy--

You are a few miles from my shop. I do French polish finishing for several builders, including Ervin Somogyi. My friend, Haiying Jiang, does the French polish work for Hill Guitar's "Signature" line. If you'd like to see what we do, give me a p.m. I'm always happy to talk guitars.

The purist in me has to ask: epoxy pore fill--why?

Trevor: Thanks for the additional insights. Maybe the safest thing for me to do, then, is what you have suggested. Definitely couldn't hurt. Would it be better to sand back to wood, instead of level-sanding the Z-poxy?

Waddy: I did not sand back to wood --- I just level-sanded the Z-poxy. I waited two days before starting the process. And, yes, as I previously mentioned, the crater is only in the area I was trying to fill the pores with pumice.....

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita