French Polishing, Grain not completely Full

[Becoming a LuLaBro]

Hey friends!

I'm currently in the bodying stage of French Polishing my 3rd build (2nd build that i'm French Polishing) and now that i've got about 2 days / 6 sessions of Polish on the guitar, i'm beginning to notice that some of the grain on my Black Walnut isn't completely full. 

I originally grain filled with 3 coats of Zpoxy, i believe it was full at the end but i may have opened some of the grain back up again when i was sanding /scraping back to bare wood.

What are my options for filling in the open grain? Is pumice powder the best option or is there a better alternative?  Full disclosure i've never actually grain filled with pumice powder, although i do have some.

Any advice is appreciated, i've included a picture of the open grain (look in the reflection of the light) for your reference & general amusement

[jwsh...@q.com]

You can pore fill at any time during the bodying sessions. I basically only use FFFF pumice for pore filling. After pore filling during the bodying stage sand back with 1000 grit paper to level and continue bodying. Scooter

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[rolert]

I use end grain dust from a scrap of the back and sides with shellac to pore fill. Put some dust on the back or sides. With shellac on a cotton ball  rub the dust into the pores in a circular motion. Then sand back with 1000 grit sand paper it may take a few rounds to fully fill the pores.

[robnewell54]

Hi - the important takeaway message from Scooter and rolert is that FP is very forgiving and you can stop at any stage in the process and go back to the previous stage without having to strip the whole thing off. It also doesn't matter what you originally filled with. You can always use pumice or dust. Consider it as if it was a repair. I doubt that you could easily drop fill with zpoxy, simply because it is a little difficult to manage in small areas, but you might be OK. You could certanly drip fill with CA glue or CA glue and dust, but you might need to start the sanding with a coarser grit and work through the grits. I'd probably go with pumice if you have used it before. Otherwise, I found the curve with dust to be shorter. Regrettably this is a situation where it is time consuming to practice on scrap, but once again, the beauty of FP is that it is reversible.

[romsmith]

I would avoid pumice like plague. If you've never used it, there's a serious opportunity to royally screw up your FP and have to scrape it back to bare wood.

If you know how to use it well, then it's your call ;)

Aquacoat is the way to go - fill at any time during the polishing process, albeit you will need a lot of coats (aka aqua-coat-it-one-more-time).

[joe]

Roman, your experiences with pumice must be quite different from mine! I started with pumice and stayed with it for a few years before I succumbed to the faster, easier, thought process of fillers like Aquacoat, z-poxy, and others. I gave them the old college try and ultimately stuck with pumice. I never found any thing that is as repeatable, and consistent as FFFF pumice for pore filling. 

There is a serious opportunity to screw up any thing if you have never used it before! In the last 12 years I have never come across a need to scrape the shellac to bare wood. I have run across some problems that required work to level an area but have always been able to save the day with pumice. You always get better results using a method when you know how to use it. I agree, stay away from things you don’t understand. But if we all did that we wouldn’t know very much!

 I could not truthfully tell folks that I use the time tested, traditional method of french polishing if I couldn’t handle using pumice like they have done for hundreds of years.  I agree with Roman about finding some thing that works for you and stick with it, after you have maybe tried some alternative methods to see if they might be an improvement over what you are currently doing.Scooter

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[Robert Newell]

I agree almost entirely (or. possibly, entirely) with Scooter on this. I found it very hard to get the hang of FP in general (despite Robbie's excellent online course, which I do recommend), and pumice filling in particular, from online instructions. However, as soon as I went to an actual luthier and polisher and took some lessons, it all fell into place. Part of the problem is that there is a ton of conflicting advice regarding pumice filling out there (which I won't add to!). So, for example, some commentators suggest you are filling the pores with pumice and 'clearing' it with shellac, while others suggest you are using pumice with alcohol alone as an abrasive, and many variants of these two suggestions. In my view, you either need to be very talented and persistent or have someone mentor you through the process of FP, including filling. However, I think it is worth the effort and go back again to my point that it is 100% reversible at any stage. I can't really see a situation where you'd have to scrape back to bare wood, but, IF you did, you could do it just for a small affected area (as in a serious repair), and the characteristics of FP mean you could blend that area in with the rest of the piece seamlessly in relatively little time.

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Rob

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[Roger Pierce]

In French polishing my last uke, I found a few areas that had pores showing. It was very easy to fill with a little end grain dust, a little fine sandpaper, then  proceed with the shellac. Very much like French polishing, but with a sprinkling of dust. Also, unlikely to cause major problems and no steep learning curve.

Roger

 

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[romsmith]

I'm not saying that pumice doesn't work - I'm saying avoid it like plague if you're not 100% sure you're happy with it, especially closer to the end of the polishing process.

Apart from the risk or pushing light-coloured pumice into pores on dark wood (ouch), there's also a particular case where the pumice-shellac-powder mix solidifies into a very hard dark-coloured surface and effectively needs to be scraped off. I believe it only happens if you have overloaded the rubber with pumice first place, but it's happened to me and several luthiers I know.

Shellac errors are easily repairable. Pumice errors are not (in my experience at least).

Aqua-coat-it-again is idiot-proof and I'm the living proof of that.

[jwsh...@q.com]

Roman, if folks only did what they are 100% sure of nobody would ever do any thing! 

I have found that pumice is basically color neutral when pore filling. For me the pumice lets the color of the wood shine through and doesn't conflict with dark wood. I have used pumice on all my builds, including dark Brazilian rosewood and Cocobolo and never experienced any color problems.

If one is inexperienced using pumice there are problems that might arise. Clumping of pumice is one such problem. I have, in the beginning,  experienced clumped pumice on the surface. I never had to scrape it off. There are methods of removing the clumps with your muneca and alcohol. The problems you are talking about are due to operator error, not the pumice. It takes time to master the learning curve of French polishing as well as using pumice. Some folks give up before experiencing success which leaves them with the idea that pumice is too be feared and avoided. I took the time to overcome the learning curve and now would not use any other type of pore filler. 

Different strokes for different folks. It is all good if you are blessed to be able to build. Scooter

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