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Pumice pore fill problem
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=50942		 Page 1 of 2
Author:  WendyW [ Sat Sep 01, 2018 6:22 pm ]
Post subject:  Pumice pore fill problem
I've been really religious about clearing the pumice on my pad with alcohol, but I've ended up with white specs in the grain....a lot. Definitely not mineral deposits because they were not there before I started pore filling. I'm using FFF pumice and Everclear. Like I said, I definitely cleared it each time I put it on the pad. idunno I'm very frustrated. So what can I do about it now? Is there a way to clear it after it is already in there? Do I have to sand the whole back down, not sure I want to take off that much of the thickness. [uncle] [uncle] Help please!
Author:  WendyW [ Sat Sep 01, 2018 6:24 pm ]
Post subject:  Re: Pumice pore fill problem
Guess I should have said I had 3 spit coats of shellac on the guitar. It is EI Rosewood. Going to be French polishing. Thanks, Wendy
Author:  jfmckenna [ Sat Sep 01, 2018 6:32 pm ]
Post subject:  Re: Pumice pore fill problem
I use a brush to apply the 'spit' coats so it's thick enough. Spit coats with a pad could be too thin but my guess is you are usy too much pumice. If you sprinkle a pit on some paper you just want to dab a bit on the pad. It's hard to explain. If it's not filled yet then if you keep on going then you may be able to slurry enough in to hide it. Like you said sanding back is not a good option. You may even want to just sand up a slurry with 320 paper and try packing it in.
Author:  WendyW [ Sat Sep 01, 2018 7:00 pm ]
Post subject:  Re: Pumice pore fill problem
The grain is not filled. What would you use to create the slurry...shellac? Maybe I should try Robbie OBrien's method of end grain sawdust rubbed in with shellac. He usually does it on a cedar neck, but I could use rosewood dust I guess.
Author:  DennisK [ Sat Sep 01, 2018 9:01 pm ]
Post subject:  Re: Pumice pore fill problem
Post back here if you ever figure it out :) I've had the same problem. What I ended up doing to fix it was pick the white bits out with a needle, then sand with alcohol on 320 grit wet/dry to grind up plenty of slurry without getting pumice in the pores. Then use alcohol and a bit of pumice on a muneca to drag it around and pack into the pores. Then scrape off any excess slurry (which now has a bit of pumice in it, which dulls the scraper quickly... so expect to do a lot of resharpening). If you can't see the excess slurry, wipe on a coat of shellac and it will become more visible as dark blotchy areas.
Author:  jfmckenna [ Sat Sep 01, 2018 9:32 pm ]
Post subject:  Re: Pumice pore fill problem
What Dennis just said... The slurry is shellac, alcohol and sawdust. When you get it just right you know it. You can sense it. You can hear it, smell it and feel it.

The pumice with an alcohol soaked pad tears wood fibers and fills in the pores. You can feel the 'sanding' action of the pad as you make circular patterns and you can see the slurry fill pores.

Like I said I always short cut it and brush on the shellac. I have not tried O'Brien's technique but it makes great sense to me. Using wet dry paper could speed up the process. Go
Author:  jfmckenna [ Sat Sep 01, 2018 9:34 pm ]
Post subject:  Re: Pumice pore fill problem
Oh one other important thing.... Do NOT use any shellac on your pad when filling. Alcohol only!
Author:  doncaparker [ Sat Sep 01, 2018 10:36 pm ]
Post subject:  Re: Pumice pore fill problem
I’m going to have to disagree on the “no shellac during filling” advice. The pumice is probably turning white because there is too much pumice and not enough shellac and sawdust mixed in with it. If you pour alcohol on pumice, and add nothing else, the pumice will go grey while wet with alcohol, but then it will go back to white when the alcohol evaporates. It needs shellac and sawdust mixed in to not revert back to white. While we can hope that the spit coats of shellac provide enough to do the job, I think it can sometimes not be enough, and/or not enough sawdust gets abraded, so the white shows up. Adding a little shellac to the pumice right on the pad, and rubbing it around, can help avoid that. So can working harder on abrading the wood with the pumice.
Author:  rlrhett [ Sat Sep 01, 2018 10:43 pm ]
Post subject:  Re: Pumice pore fill problem
FWIW, I do use shellac and don’t have the problem you are describing. My guess is you are using too much pumice.

I start with a thumb sized rubber. The wadding is damp but not wet with alcohol. When dabbed on my wrist it feels cool, but not wet. With one finger I dab at a small pile of pumice that I poured out on a piece of paper. The little bit that sticks to my finger I wipe onto the rubber. Then I add three or four drops of shellac. Just enough for the pumice to wet and look grey, not white.

It should feel like sanding with fine sand paper. If you are sticking to the wood, you are using too much shellac. If it doesn’t feel like sand paper anymore, another dab of pumice and another couple of drops of shellac.

You should be able to get rosewood dust to fill over your white specks. Likewise, a first session of bodying up will probably make it invisible. If you really need it gone, and it was applied dry with just alcohol, I would suggest hitting it with compressed air.

Traditional FP has been used on rosewood for centuries. No need IMHO to reinvent the wheel.


Sent from my iPhone using Tapatalk Pro
Author:  jfmckenna [ Sat Sep 01, 2018 11:10 pm ]
Post subject:  Re: Pumice pore fill problem
doncaparker wrote:
While we can hope that the spit coats of shellac provide enough to do the job, I think it can sometimes not be enough, and/or not enough sawdust gets abraded, so the white shows up. e .


Ah but see? There's yer problem.... You need to have a good shellac base, is why I was saying I use a brush for spit coats, to then pumice fill. Adding shellac to the pad when pumice filling is problematic. It's best to put the shellac away for filling.
Author:  doncaparker [ Sun Sep 02, 2018 8:00 am ]
Post subject:  Re: Pumice pore fill problem
Well, it’s Wendy’s problem, not mine, thank goodness! :D

I think we agree on what is causing the problem: the pumice is not getting mixed with enough shellac and sawdust to help it stay the color of rosewood when the alcohol evaporates. I agree with you that putting enough shellac on in the first place is a good way to prevent the problem. I’m just saying that some folks (including me) can get there a slightly different way. There are dangers both ways. With your way, the danger is that the pumice makes its way into the pores without abrading enough sawdust and melting enough shellac to mix up well. I think that is what Wendy has experienced. With my way (adding a little shellac to the pumice on the pad), the danger is winding up with too much shellac in the total mix, which gums up the process. Either way, I think being mindful of the process and being flexible and responsive to what is happening at the moment are key.
Author:  WendyW [ Sun Sep 02, 2018 8:31 am ]
Post subject:  Re: Pumice pore fill problem
For what it is worth, it was 3 thick coats of 2lb shellac that was on there. Maybe I was using too much pumice, but I thought I was just biting off a tiny bit. I know for sure I was using too much alcohol. Where the grain has filled it looks ok, where the grain hasn't filled is where the white in the grain is showing. I will try hitting it with compressed air, although I think it is pretty well stuck in there. I will also try the needle idea where it is worst. I like the idea of sanding up a slurry, just still unsure whether to use shellac or alcohol with the sandpaper.
Author:  doncaparker [ Sun Sep 02, 2018 9:33 am ]
Post subject:  Re: Pumice pore fill problem
Wendy—

When you were using too much alcohol, do you think you wiped off a lot of the spit coats of shellac, or is it still on the guitar? I think the answer to that question can help you figure out whether to use just alcohol, or alcohol with some shellac. Keep in mind that the idea of using only alcohol at the filling stage assumes there is enough shellac already on the guitar to mix with the pumice and sawdust and make a good brown slurry. If there is not enough shellac still on the guitar (from maybe using too much alcohol and wiping it off, taking the shellac with it), then you might need to add some. This is a hard thing to gauge if you are not there in person, unfortunately.
Author:  WendyW [ Sun Sep 02, 2018 11:23 am ]
Post subject:  Re: Pumice pore fill problem
Don, I think I probably wiped a good amount of it off. When you say add some, do you mean to just wipe on some more spit coats, or use shellac with sandpaper to make a slurry?
Author:  doncaparker [ Sun Sep 02, 2018 1:09 pm ]
Post subject:  Re: Pumice pore fill problem
In deference to those who follow the Milburn approach (which is, I think, what you were following), you can just wipe on more spit coats, let them dry, then start the filling process again with less pumice this time.

Maybe the sandpaper will work, too. I've not experimented much with that at the filling stage.
Author:  Michael.N. [ Sun Sep 02, 2018 3:56 pm ]
Post subject:  Re: Pumice pore fill problem
WendyW wrote:
Don, I think I probably wiped a good amount of it off. When you say add some, do you mean to just wipe on some more spit coats, or use shellac with sandpaper to make a slurry?


That's how I've been filling pores lately. I put a retarder in the shellac, dip the abrasive in it and sand with the grain. Just like the oil sand fill but with shellac. It's a bit messy and you certainly wouldn't want to sand near any light coloured inlays. Like many pore fillers it shrinks back so needs two or even three applications. It's a little different with yours because you've used pumice. Sanding might cut into the pumice making matters worse and revealing more white specs. I seem to recall doing that many years ago. Then again the slurry might be enough to stain what pumice is already present. I suppose you could try to recreate the white pumice flecks on an off cut and see of the sanding does the trick.
Author:  gregorio [ Mon Sep 03, 2018 8:18 am ]
Post subject:  Re: Pumice pore fill problem
If I remember correctly, its along the lines of what rlrhett mentioned.

I remembered having the same problems when attempting FP.

When I paid closer attention to making sure the pumice was "saturated" so to speak, the specks were greatly reduced.
I may also have been making the mistake of using too much pumice and trying to compensate with more alcohol.
Placing some pumice on some paper, I experimented with adding alcohol and observing the change to the pumice.

FP was how everyone explained it, and couldn't explain it to me.
You basically have to work it out and develop the feel by doing.

Its been awhile now and I have only done 2, so not an authority on the process but I am a beginner with beginner problems. : )
I really enjoyed the FP process, frustrations and all. I will however be trying epoxy pore-fill on my next build.
Author:  Alan Carruth [ Mon Sep 03, 2018 10:15 am ]
Post subject:  Re: Pumice pore fill problem
I'm in the camp that starts with minimal shellac, and adds to it as you go along.

The problem with not having enough shellac is that you end up with loose pumice on the surface and in the pores. Adding some more shellac as binder fixes that. The problem with too much shellac is that you end up with mud on the surface. It's hard to pick up the excess with alcohol on the pad without pulling some of the filler out of the pores, and the presence of the pumice (glass) in the mud makes it very resistant to sanding if it's at all thick. To me the problems of too little shellac are less problematic and easier to remedy than those of having too much. I will note that I spend a fair amount of time working up some wood dust and making sure the pumice that's there has at least some shellac mixed in with it. Pumice that has been well wetted with shellac will not show up white, since it's actually a pretty much transparent material. The trick of pumice filling, then, is to get just the right balance of shellac and pumice. I find that easiest to do by sneaking up on it.
Author:  WendyW [ Mon Sep 03, 2018 11:30 am ]
Post subject:  Re: Pumice pore fill problem
Thanks for all the answers. This is the 5th guitar I have french polished. I enjoy the french polish process from bodying on, but after no problems whatever pore filling the first one with pumice, all the other pore fills have been a pain. I am with Gregor on this. No more pumice for me. I will try epoxy next time. In the past I have had much more success with pumice when I have found a few unfilled pores after bodying, which makes me think that it definitely goes better when there is ample shellac on the guitar. So I will chalk this up to...not enough shellac on the guitar to begin with, and using too much pumice and too much alcohol.

I tried placing a drop of shellac onto the pumice in the worst pore too see if it would clear the pumice and it did not. I tried blowing it with a blast of air, and I tried strong suction. Nope. Then I wiped the back with alcohol to take off the excess pumice and probably what was left of the shellac. I ended up using one of Robbie OBrien's methods. I made end grain rosewood sawdust and applied it with a cotton ball with 1 lb shellac, 2 coats. After it dried I sanded with 220. After 2 coats it had filled most of the incompletely filled pores over the white pumice specks. There are a few places where the grain must have been completely filled and there is a tiny bit of white, but I think I am going to have to live with it at this point. I am going to do a couple more coats today and then sand with 320. Haven't decided what to do with the sides for pore fill, but no more pumice for me.
Author:  Kathy Matsushita [ Wed Sep 05, 2018 11:00 am ]
Post subject:  Re: Pumice pore fill problem
I am by no means any sort of expert on pore-filling with pumice (I've just done it once). But Tom Bills, whose French-polishing course I've been following, has a slightly different method. He has a pad of cheesecloth only, and first dabs the pad with alcohol. Then he uses his finger to dab some pumice onto the pad, and next dabs a fingerful of shellac (2-lb cut) onto the pad. He says that it's the shellac that will clear the pumice, as the alcohol evaporates too quickly and leaves the pumice often turning white. He rubs the shellac onto the pumice till he's sure it's totally cleared the pumice. Then he starts using the pad to work the pumice into the pores, using circular motions.

I've tried this only once and never got white specks.
Author:  bionta [ Wed Sep 05, 2018 11:15 am ]
Post subject:  Re: Pumice pore fill problem
Kathy Matsushita wrote:
I am by no means any sort of expert on pore-filling with pumice (I've just done it once). But Tom Bills, whose French-polishing course I've been following, has a slightly different method. He has a pad of cheesecloth only, and first dabs the pad with alcohol. Then he uses his finger to dab some pumice onto the pad, and next dabs a fingerful of shellac (2-lb cut) onto the pad. He says that it's the shellac that will clear the pumice, as the alcohol evaporates too quickly and leaves the pumice often turning white. He rubs the shellac onto the pumice till he's sure it's totally cleared the pumice. Then he starts using the pad to work the pumice into the pores, using circular motions.

I've tried this only once and never got white specks.


Ditto. I also have done this only once, by Tom Bills’ method with good results. I French polished Honduran mahogany, walnut & Sitka spruce. It was not difficult to do or to get the feel of it but it did take some time.
Author:  Alan Carruth [ Wed Sep 05, 2018 11:42 am ]
Post subject:  Re: Pumice pore fill problem
I have to say that I've never had that problem either, so it's hard for me to offer advice as to how to clear it up. Unlike Kathy, I've had a lot of experience with it: I used FP as my main finish for a few years, and have instructed a number of students. Even when I don't use shellac as the main finish I have often used a pumice/shellac fill. All I can say is that what appears to be key to me is to see that the pumice is always 'cleared' with sufficient shellac, so that the transparent particles of the pumice have a shellac coating and there are no air spaces. I find that easy to accomplish with less shellac and more alcohol early in the process, but that's just my experience.
Author:  Michael.N. [ Thu Sep 06, 2018 4:01 am ]
Post subject:  Re: Pumice pore fill problem
Yesterday I tried a few tests with the pumice. I sprinkled some pumice onto a piece of walnut and wiped the excess off with the hand, going across the grain. Of course there's white specks everywhere, it's dry and there's nothing to clear the pumice. Then I took a pipette and armed with a 1lb cut of shellac I pooled it over the pumice/pores. It clears it. Even if you wipe the excess shellac over other areas of dry pumice it clears it - providing there's a sufficient amount of shellac. I had one very small area that showed white pores. That was the area where I wiped across it and there was insufficient shellac. Here's the rub (pardon the expression). Once those white specks appeared it then proved impossible to clear them. Even pooling a very large amount of shellac in that area failed to clear it and that was applying some 5 minutes after the white specks appeared. I think it all goes to prove that it's a balance between the right amount of shellac/alcohol with the right amount of pumice. Too much pumice and not enough shellac/alcohol will likely lead to the white specks - as many have previously stated on this thread. In that sense it's better the err on the side of caution in respect of the amount of pumice, at least until one has got the feel for it.
Author:  DennisK [ Thu Sep 06, 2018 4:32 am ]
Post subject:  Re: Pumice pore fill problem
Michael.N. wrote:
Yesterday I tried a few tests with the pumice. I sprinkled some pumice onto a piece of walnut and wiped the excess off with the hand, going across the grain. Of course there's white specks everywhere, it's dry and there's nothing to clear the pumice. Then I took a pipette and armed with a 1lb cut of shellac I pooled it over the pumice/pores. It clears it. Even if you wipe the excess shellac over other areas of dry pumice it clears it - providing there's a sufficient amount of shellac. I had one very small area that showed white pores. That was the area where I wiped across it and there was insufficient shellac. Here's the rub (pardon the expression). Once those white specks appeared it then proved impossible to clear them. Even pooling a very large amount of shellac in that area failed to clear it and that was applying some 5 minutes after the white specks appeared. I think it all goes to prove that it's a balance between the right amount of shellac/alcohol with the right amount of pumice. Too much pumice and not enough shellac/alcohol will likely lead to the white specks - as many have previously stated on this thread. In that sense it's better the err on the side of caution in respect of the amount of pumice, at least until one has got the feel for it.

Great test, and the result makes sense. You can use that same behavior to manipulate the appearance of the wood under finish. Slop shellac on a bare wood surface and it will soak in and give a deeper appearance. Wipe it on with a relatively dry cloth and it will seal the wood without penetrating, after which you can layer on more shellac and it will keep a flatter appearance more like bare wood.

I'll definitely be paying more attention to shellac management next time I'm pumice filling. Seems likely that my problem has been running out of shellac from the spit coats before the pores are completely filled, and then continuing to rub with just alcohol and pumice, which doesn't stick in the pores well to begin with, and dries white if it does.
Author:  johnparchem [ Thu Sep 06, 2018 11:03 am ]
Post subject:  Re: Pumice pore fill problem
I really appreciate the members comments above where it is emphasized that you need to feel what is happening; add shellac, pumice and alcohol as needed.

I think the Millburn brothers, who wrote a truly wonderful guide for french polishing, led people wrong with their very strong statement of getting rid of the shellac bottle while executing a pumice fill. On my first guitar I worked many hours with almost no results when I tried to pumice fill following their pumice fill description; I then watched Louis Fernandez DVD French Polishing for Guitarmakers and pore filled the entire guitar in less than an hour. Louis Fernandez method violated every admonishment put forth in the Millburn description such as more shellac and pounce bags for direct application of pumice when needed. The finish on that guitar still looks good 8 years later with no pumice showing in the pores.

I am sure the statements about not using shellac once you start with pumice was a counter to a tendency of people using too much.
I am sure the Milburn method worked for them, although I heard they may have switched to epoxy, But a strong statement like they made had to depend on the right amount of shellac left on the guitar when applying the spit-coat. If there is not enough shellac to bind the fill inexperienced finishers are left wondering if somehow their technique with the pad is wrong. In that case the only way to go forward is to add more shellac.
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