Official Luthiers Forum!

Hi, I`m hoping for advice. I have filled my previous six guitars using pumice and shellac with good results. I use French polish to finish. I am about to pore fill my latest build and I am considering giving epoxy a try, probably Z-poxy finishing resin.
My concern is that if I need to carry out finish repairs in future and use pumice in the process then I may encounter problems with epoxy being lifted into the shellac.
Has anyone experienced this or is it not a problem?

Thanks

Roy.

I have no experience to offer but am wondering why you would have to go to pumice for a finish repair? Would you not just be French polishing your repair?

_________________
Bryan Bear PMoMC

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

Bryan, I`ve used the Milburns` tutorial to learn to French polish and they use pumice in scratch repair.

https://www.guitarsint.com/article/FAQs

I understand that they are talking about scratch repair to the top and also that the aim is not to abrade through to the wood. My query only really relates to the back and sides (Indian Rosewood). Whether to leave a layer of epoxy on the surface as a safeguard or to sand back leaving just the pores filled. I know that I could test on scrap but the results after a few days curing may not be the same as those after a few years.
I wondered if anyone had been there and done that.
Pros and cons?


Roy

Roy

If you sand back the epoxy to wood you will lose the grain pop coming from the z-poxy. However, if you leave a thin coat of z-poxy on you'll get the grain pop but you'll have to be careful in any of your repairs that you don't go through the z-poxy when executing the repair. Any spots where you go through the z-poxy stick out badly.

Hope that helps.

Brad

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

Yep! I would think that using pumice and shellac to repair a scratch would look the same as a shellacked/French polished surface as long as 1) the epoxy is only in the pores, or 2) the scratch didn't go through the epoxy layer. But, if you leave a thin layer of epoxy on the wood before you shellac, any scratch that goes through the epoxy will not look the same after the repair. Perhaps you could remove the surrounding shellac, repair the scratch with epoxy then build the FP back up and blend?

I'm not sure I would let deep scratch repair weigh too heavily on my choice of finish though. You would hope it never sees damage down to bare wood and if it does a well done but somewhat visible repair is not so bad. If you like the look of epoxy popping the grain, go for it and try not to bang it around too much in use.

_________________
Bryan Bear PMoMC

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

Thanks Brad and Bryan, Very helpful. On the strength of your input I`m leaning toward sanding back to the pores.

Roy

If you have good results with pumice and shellac for pore filling I would stick to that.
I pore fill with epoxy because I laminate with epoxy. It bleeds through the surface veneers and pore filling evens out the surface appearance. It is somewhat nasty stuff (icky sticky) to work with and I don't think it offers any great advantage over other pore fillers. It is affected by UV just as some other finishes are so in my opinion should always be top coated. When building fiberglass clad boats a protective layer of varnish is needed to keep the epoxy looking good.

Milburns tutorial says to sand back epoxy fill to wood. It's what makes the most sense imho. It's just like a typical oil based fill. You just want the pores filled that's all. Slather the epoxy on and scrape it off then sand back to wood leaving the pores filled. No worries about any future repairs.

I think you are getting confused because pumice fill works by creating a saw dust slurry and if the whole surfaces is coated in epoxy then you will not be able to create such a slurry. You should not have to worry about filling pores on repairs anyway.

Thanks Clay S. and jfmckenna, I am reassured. My reason for considering using epoxy filler is to save time and effort. I enjoy French polishing and building the finish but I find pore filling a drudge. I also find it difficult to not stain the bindings and side purfling when moving the slurry about. I get there eventually while thinking "there has to be an easier way than this". My technique must be poor, it takes me forever.
My original intent was to fill and leave a surface layer but I`ve decided against that after reading your comments. I have a random orbital sander and a shop made cylindrical Abranet hand sander to use on the waist: both connect to my dust extractor. With care I`m hoping to get the excess epoxy removed quickly.

Roy

I dare say you will have a hard time finding anyone who enjoys pore filling

I've only used epoxy once and it was on a Uke. I used 5-minute epoxy just like Milburn does and it worked quite well actually. Bare in mind though, even though it says it's 5-minute, give it 24 hours before sanding, or at least 'over night.'

That`s encouraging. I`ve ordered some Z-poxy and some Devcon 5 minute epoxy. I`ll experiment with both and see how it goes.
Thanks again to you all for your help.

Roy.

I have used epoxy for pore fill many times but never did french polishing. I know cured epoxy is compatible with shellac so it should be fine.

If you are doing a test panel I would do a section with the epoxy just level sanded, and maybe one sanded to the bare wood. My guess is you'll like the first one better for two reasons. The 1st is sanding back to bare wood, while leaving the pores filled is a lot harder to do in practice than theory. And the 2nd is it seems to me that it would be nice to have a hard surface below the relatively soft french polish.

_________________
Joe Beaver
Maker of Sawdust

Joe, I`ll try that. I like the idea of a hard barrier beneath the shellac. However I have a feeling that getting that thin surface perfectly level without sanding through may be difficult. Maybe I`m overthinking this. I`m sure that when I start working with the epoxy and get a layer of shellac on I`ll have a better idea of which method to use.

Roy

People like the Zpoxy becasue it pops the grain. I think it would be difficult to not sand through it too and I also have reservations about using epoxy as a coating. But that just opens a can of worms

I`ll find out when I get hands on. From my experience shellac pops the grain very nicely but it will also highlight tiny imperfections in surface preparation.

Roy

"Bare in mind though, even though it says it's 5-minute, give it 24 hours before sanding, or at least 'over night.' "

I try to let the epoxy fully cure before doing any sanding. I wait about a week. Uncured epoxy can be a sensitizer and some people develop an allergic reaction to it. I also try to avoid any skin contact with uncured epoxy.


"My reason for considering using epoxy filler is to save time and effort."

It's never really worked out that way for me. I think using oil based fillers are probably the easiest way to go. I haven't done the pumice and shellac thing, but I wouldn't think it would be any more difficult than the epoxy.
Todd Stock has some videos on epoxy pore filling:
www.youtube.com/watch?v=YYHxMg7n9cI

The Todd Stock videos are impressive. Looks like that`s the way to go if you intend to leave epoxy on the surface before finishing.
I`ve not used oil based filler. I`ll have to look at that. How do you match the colour?
I did use a water based filler on my first guitar. It was African mahogany and I decided to stain it to try and get the dark Martin mahogany colour. After staining it looked fine until I started pore filling. I used a black stained filler and let it dry for too long. It looked like a lump of guitar shaped rock I can laugh about it now but it was a Very Bad Experience. I did manage to get back to the wood but then of course I`d got a mottled stain. And on it went from there! That`ll never happen no more. I haven`t used stain since, the wood is the colour it is. It always looks darker ( and nicer) under finish anyway.
I like the fact that using pumice and shellac causes no colour problems and I am hoping to find the same with epoxy (though apparently I could get the dreaded amine blush!)

Roy

With oil based fillers you want to remove the excess with a squeegee and after it has hazed over (but before it dries) by rubbing it with burlap. With many fillers you can add pigment stain to modify the color. The filler reacts differently than the wood to UV exposure, so that is one downside to using them on an unstained piece.

Thanks for the advice Clay. The epoxy has arrived and the games will begin after Christmas.

Roy.

French polish over epoxy pore fill works just fine. This is a preferential solution for me with classical guitars where the neck finish is worn due to chemical reaction with the owner's body chemistry. I've never had an issue, and find that the finish is both sturdy and touches up great with the usual french polish maintenance.

Andy

Andy, are these repairs to traditionally filled French polished and worn necks, or is it on instruments that you have built and initially pore filled with epoxy? If the former are you removing the original neck finish or do you not find this necessary.
Thanks,

Roy

Just one quick note. As others have said, be sure your epoxy is fully cured before you start with the polishing. How long depends of the temperature it will cure at. If you can keep it above 70 degrees F it will probably be ready in 2-3 days.

And... zpoxy is prone to blushing if applied during times of high humidity. If that is the case you can usually prevent it by warming the wood surface with a hair drier just before applying. That will drive off the moisture.

I know, the epoxy thing sounds quite scary at first but after you have done it, most likely it will be your favorite filler.

_________________
Joe Beaver
Maker of Sawdust

FWIW, I am beginning to believe that pumice/shellac is one way of getting a really good final leveling even if you are not pore filling. After all, it's not the pumice that fills the pores. Tom Bills mentions using pumice on maple, which got me to try on a small headstock. He was right, somehow the finish came out better. My theory is that the pumice leveled the maple and/or shellac base coat. But it could be little green men beaming it up at night for all I know. The headstock was several layers of maple and black fiber veneer that had been laminated with epoxy. As I usually do, I did a wash coat of epoxy to even out any weep through of epoxy during lamination.

I've not tried a full back or top yet, but that is on the endless "experiments" list.

That`s interesting. So if you did level the maple your base coat became a clear mix of cured epoxy, shellac, maple fibres and pumice? What finish did you use?

Roy

Both, Roy. But I meant to emphasize that I've had particularly good luck where human chemistry was eating guitars alive. In the case of body chemistry finish failures, and well any finish failure really, the finish needs to be removed as it has failed. So on the necks it is a strip, epoxy pore fill, and FP finish. I've done instruments as well, fresh - of course that works well. BTW once the finish is stripped on a repair, it invariably opens pore (say, on Mahogany) so fill is necessary.

Merry Christmas to you.

Andy