BYO: French polish grain filling

Craig Bumgarner · April 2009

BYO: (Build Your Own): I'm in the finishing stage and am trying to fill walnut grain in the french polish method and am getting absolutely nowhere. Any one have any ideas.

I'm using the Orville & Robert Milburn on-line tutorial and followed steps carefully (I think): Three "spit" coats, allow overnight dry, with alcohol and pumice only, rub out 2-3 times to fill grain. Well, I'm up to 20 times and no filling. I stripped the three spit coats off and applied one light coat, no change. I've tried varying amounts of pumice, alcohol and even more shellac. Nada. I'm stumped.

Had this same problem on the last guitar using bubinga backs and sides. Never got the grain filled in the early stages or as the body coats went on. Am determined to get the grain filled properly early on, but so far no luck at all. Thoughts?

Off to MIMF.com to see if they have any ideas.

Craig

Peter Davies · April 2009

Hi Craig,

I understand your frustration with the grain filling. I had the same problem and it seemed to take forever. I finally got there in the end after hours of fun but then read the final part of the Milburn instructions (FAQs).

http://www.milburnguitars.com/fpbannerframes.html

They refer to alternative methods of grain filling

"Five-minute epoxy: ........we are now using this method of grain filling almost exclusively. "

That could save some time.

It also seems they have two web sites with French Polishing instructions. The one with the above line is the one with full colour pictures.

Best of luck inspecting some original Macs.

Cheers,
Pete

Craig Bumgarner · April 2009

After posting last night, I searched the MIMF archives. There are a number of threads and posts on grain filling w/ French Polish (FP). Unfortunately, there are as many opinions as there are posts.

I came away with two ideas that I applied this morning. One is to use lots of alcohol to move the top layer of existing shellac, just a little pumice and get a thin slurry going that will fill the grain. The slurry is constantly changing as the alcohol evaporates and the consistency is important, so this takes a little practice.

The second, equally important idea is to use a light touch while rubbing. As the MIMF poster said, it is counter intuitive, but I found this morning this really makes a big difference. A light touch keeps from pulling the slurry (filler) back out of the grain as you rub. I found rubbing a little harder intially in a small spot to get the slurry going and then lighten up to finish worked best.

I worked in patches of about 4-6 square inches, not in lines because the slurry dries out before the end and a recharge of alcohol is needed.

The results of this morning's session are not perfect but much better. I think another session will do it.

I'm sort of determined not to give up on this. People have been grain filling with rubbed shellac for centuries, and it is a trick I'd like to have in my bag. Once it is however, I'm going to try the epoxy method that Peter mentions, sounds like a reasonable and probably much faster way of grain filling. I've seen it argued that epoxy filling changes the acoustics of the back and sides (the spruce top does not need grain filling) but 1) it could easily be for the better, not worse and 2) With laminated backs and sides, I can't see that it can possibly matter, there is already a pile of glue involved.

Craig

Bones · August 2020

Hi Craig. Old post. Thinking of trying French polishing on both walnut and rosewood. I'm wondering what you ended up with for grain filler and shellac? Thanks

ChrisMartin · August 2020

I do not know if it is used on guitars, I have not tried, but I took a course many years ago in antique furniture restoration and it is common practice to rub in some plaster of Paris with linseed oil to fill grain and then coats of shellac. Not too much oil as you will need to leech it out later but the plaster takes the shellac and matches the color.

Could be worth trying on a scrap piece first.

mac63000 · August 2020

Would filling grain be noticeable under french polish? Or does it go in clear? Just asking out of curiosity.

Bones · August 2020

I was thinking about getting some grain filler from LMII and then French polishing over that with shellac. Not sure where is the best place to get the shellac though. Anyone used the pre mixed stuff from Home Depot? I used it on some other projects and seems pretty nice just not sure how it would do on a guitar. Otherwise I guess I can source some flakes and mix my own.

mac63000 · August 2020

https://www.djangobooks.com/forum/discussion/comment/103188#Comment_103188

Went down a small rabbit hole and answered my own question...

Seems like this would do the trick:

https://www.stewmac.com/luthier-tools-and-supplies/supplies/finishing-supplies/fillers-and-putties/colortone-powdered-grain-filler.html

ChrisMartin · August 2020

https://www.djangobooks.com/forum/discussion/comment/103188#Comment_103188

As I said, the antique furniture trade use plaster of Paris and it takes the color of the shellac. On dark furniture, like oak, it adds a very fine golden highlight to the grain, hard to explain without seeing it but it works and looks good. For guitars with a spruce or cedar top it would blend in perfectly, if used on, for example, mahogany it would just highlight the grain. Of course if using any wood dye to stained the timber that will take the stain to match if desired.

If you can find scraps of various timbers, light or dark, close grain or coarse, a few test pieces will give an idea.

jared · August 2020

In my experience of using it for 25 years or so on many, many instruments, I feel pumice is the cheapest and best thing to use under french polish. It takes a little effort and time to get the technique, but once you have it down, it goes pretty fast and easy. It takes me about an hour or two to fill a rosewood back and a little more to do the sides (curves make it tricky!). This fills the pores with a very hard mixture that is very stable over time, is easy to repair or improve at a later date, and gives off almost no toxic vapors (at least if you can get fairly pure ethanol). In addition, the color match is always naturally perfect.

Basic method is this: After you have applied a spit coat or two of shellac, you use a small cloth pad with just alcohol and a small amount of pumice on the pad to 'polish' the surface of the wood. As you rub, the wood, pumice, and shellac combine to form the filler. I advise against using oil as a lubricant at this stage of french polishing, but some people do and they make it work. Less pumice is more; too much and you will get bits that haven't absorbed shellac and these can go white later. The amount you need to do back and sides probably amounts to no more than a few grams. Use too much alcohol and you wash all the shellac out so it won't fill. Keep the pad damp and just slightly gritty with pumice. You can use a 'pounce bag' of pumice to very lightly dust the surface ahead of your pad, but make sure the pumice is 'cleared' by absorbing alcohol. Don't think of the pumice as a filler, but rather as the fine abrasive that makes the pore filler with the elements that are there on the surface. Finding the right combination of alcohol, pumice, and pressure is the trick. Work small areas at a time and go slow.

One of the many neat things about this method is that if you find a missed spot some time later in the FP process (and this will almost certainly happen) you can just go ahead and fill it the same way because the materials and chemistry are the same all the way through the finish, top to bottom. You can't really do that with the commercial pre-mixed fillers.

There are lots of good FP tutorials out there and so many small and large variations on what I just described. LMII website has a great description of the whole thing. Musical Instrument Maker's Forum has loads of advice. Good luck.