Shellac as finish?

[rogthefrog]

Originally Posted by Frank Ford

I'd say that when I'm building a finish that way, I may pass the shellac-charged pad over any given area of the finish about once a second, with the shellac being deposited and alcohol flashing off at each stroke:



As the film builds, it becomes more delicate, so it's necessary to sense and adjust technique continuously. Takes practice to get the "feel" of it, and if you think that doesn't apply to you, well, you're thinking wrong.

Practice. . .

I've seen that trail before, with shellac. Sounds like I may want to practice a lot on some scrap before I work on the real thing.

Since shellac application "actually pushes the material down into pores, scratches and other divots, allowing the material to be spread thinly without lumps," is it correct to assume pore-filling isn't necessarily required or advantageous if you're doing a shellac French polish finish?

Also re. pore filling, I've seen all manner of wild substances uses for pore filling, from epoxy to dyed drywall joint compound (!!). And when I ask the various woodworkers and supply store people I know, they have no idea what "pore filling" is, much less what product to recommend for it. Is drywall joint compound really viable for this application? I'm not a fan of epoxy in general, so if there are easier to handle pore-filling products, I'd be in favor of that.

I appreciate the advice!

[Howard Klepper]

If the wood is one that needs pore filling for a poreless finish, it needs filling with a shellac finish just as much as it does with lacquer.

So far as I can tell, no pore filler works as you would really want it to--one coat, wipe on-wipe off with perfectly level pores. If you get a good fill doing it twice you are doing OK. And be ready to be disappointed when your finish coats go on and the fill sinks, or turns out to only have been "bridging" the pores. Refill sooner than later. Like so many things in finishing, fixing a flaw in the pore fill is more work the further you are in the process.

One way that is available if you French polish is filling with pumice; actually a slurry of thin shellac, pumice, and fine sawdust. See here: https://www.guitarsint.com/article/H...assical_Guitar

I have had good results with drywall compound mixed with dry powdered artist pigments. Actually, spackle has worked even a bit better. Some people use universal paint tinting colors to color it. These wall fillers have the advantage of drying really fast and sanding very well. I've tried other water based products made specifically for pore filling that don't work as well.

Remember, pore filling is a PITA and the plate glass finish is one of the curses of lutherie. Nothing works to fill pores as you would hope it to. Approach it with that expectation and it won't be as frustrating.

[rogthefrog]

Originally Posted by Howard Klepper

If the wood is one that needs pore filling for a poreless finish, it needs filling with a shellac finish just as much as it does with lacquer.

So far as I can tell, no pore filler works as you would really want it to--one coat, wipe on-wipe off with perfectly level pores. If you get a good fill doing it twice you are doing OK. And be ready to be disappointed when your finish coats go on and the fill sinks, or turns out to only have been "bridging" the pores. Refill sooner than later. Like so many things in finishing, fixing a flaw in the pore fill is more work the further you are in the process.

One way that is available if you French polish is filling with pumice; actually a slurry of thin shellac, pumice, and fine sawdust. See here: https://www.guitarsint.com/article/H...assical_Guitar

I have had good results with drywall compound mixed with dry powdered artist pigments. Actually, spackle has worked even a bit better. Some people use universal paint tinting colors to color it. These wall fillers have the advantage of drying really fast. I've tried other water based products made specifically for pore filling that don't work as well.

Remember, pore filling is a PITA and the plate glass finish is one of the curses of lutherie. Nothing works to fill pores as you would hope it to.

Right, pumice was another one of those substances that seemed really odd to me. Thanks for the reminder.

Spackle!

Funny the kinds of things people have used for this purpose.

Thankfully I'm not all that interested in a glass-like finish. I'll look at the link you posted and experiment.

Thanks!

[redir]

I don't get the physics and chemistry that would occur to the finish due to pressure. I know every French Polisher since the beginning of time says that pressure hardens the finish but I never really read a good explanation of why that might happen.

I think my favorite pore filler today is egg whites. I still use the oil based paste fillers too. I've tried all kinds of fillers but not drywall, that sounds intriguing. Many people use epoxy too. I like the egg whites because it's non toxic and it's a great conversation piece

[Rodger Knox]

CA works pretty nicely for pore fill. You can get them filled with a single application, but then sanding back to bare wood is a real chore. Two lighter coats work better and is actually quicker, there's less time sanding back to bare wood. I've considered using CA as a finish, but I haven't figured out how to apply it evenly enough to make that work.

[rogthefrog]

Originally Posted by redir

I don't get the physics and chemistry that would occur to the finish due to pressure. I know every French Polisher since the beginning of time says that pressure hardens the finish but I never really read a good explanation of why that might happen.

I think my favorite pore filler today is egg whites. I still use the oil based paste fillers too. I've tried all kinds of fillers but not drywall, that sounds intriguing. Many people use epoxy too. I like the egg whites because it's non toxic and it's a great conversation piece

Haha, yes, egg whites. I knew I was forgetting a bunch of other wacky pore fillers. Are egg whites used as-is? I.e. crack eggs, separate the whites into a bowl, and paint the wood with the stuff?

Just to recap, for my own reference:

* epoxy
* pumice + alcohol
* drywall joint compound
* spackle
* egg whites
* cyanoacrylate glue
* shellac + pumice + sawdust

[Frank Ford]

Originally Posted by redir

I know every French Polisher since the beginning of time says that pressure hardens the finish but I never really read a good explanation of why that might happen.

Here it is, plain and simple. Rub hard and you generate some heat, which causes the alcohol to evaporate faster. During the finish building coats, it may or may not be appropriate to increase pressure for that reason. Once again, it's ALL about practice and experience.

You'll never catch me saying that by pressing harder you compact the molecules more tightly together!

In the final spiriting off, I'll often increase pressure as the finish begins to harden at the very surface. Remember, the full finish has already had time to dry thoroughly, and the spiriting off is analogous to buffing a lacquer finish. As I get to the very end, I'll drop the pad and use just the palm of my hand to rub increasingly faster and harder until my hand gets almost painfully hot. That process has the effect of glazing the surface to a very high shine, and takes only a short while, so I don't get stress and strain on the old joints.

[rogthefrog]

Do we know how old French polishing with shellac is as a practice? The bug secretion has been around forever, humans have been making alcohol and wood furniture for thousands of years, so I'd expect ancient peoples well before year 0 were already using it.

[Rodger Knox]

Originally Posted by Frank Ford

As I get to the very end, I'll drop the pad and use just the palm of my hand to rub increasingly faster and harder until my hand gets almost painfully hot. That process has the effect of glazing the surface to a very high shine, and takes only a short while, so I don't get stress and strain on the old joints.

That also works with oil varnish. I guess that's a real hand rubbed finish.

[Quickstep192]

I finished a banjo with a sprayed shellac finish a while back and it's held up well and looks nice. I don't have scientific evidence, but I swear that shellac mixed from flakes is tougher than the canned stuff.

[mirwa]

Originally Posted by rogthefrog

Haha, yes, egg whites. I knew I was forgetting a bunch of other wacky pore fillers. Are egg whites used as-is? I.e. crack eggs, separate the whites into a bowl, and paint the wood with the stuff?

Just to recap, for my own reference:

* epoxy
* pumice + alcohol
* drywall joint compound
* spackle
* egg whites
* cyanoacrylate glue
* shellac + pumice + sawdust

Also UV gel, one of my favourite pore filling compounds.

Steve

[rogthefrog]

Originally Posted by mirwa

Also UV gel, one of my favourite pore filling compounds.

Steve

What's that?

[Quickstep192]

I think it's a filler that's cured using special UV lights.

A local luthier friend uses UV cured finishes. Sounds way cool.

[redir]

Originally Posted by rogthefrog

Haha, yes, egg whites. I knew I was forgetting a bunch of other wacky pore fillers. Are egg whites used as-is? I.e. crack eggs, separate the whites into a bowl, and paint the wood with the stuff?

Just to recap, for my own reference:

* epoxy
* pumice + alcohol
* drywall joint compound
* spackle
* egg whites
* cyanoacrylate glue
* shellac + pumice + sawdust

Yes and no. Yes it is just the egg whites as they come right out of the shell but no you don't just paint it on. It's actually similar in principle as pumice and alcohol. With the traditional pumice method you first put a coat or two of shellac on the guitar. Then you load the pad with alcohol and a bit of pumice (there is absolutly no shellac used at this time). The pumice is an abrasive. As you swirl the pad around the alcohol dissolves the shellac and the pumice draws up saw dust which makes a slurry that gets packed into the pores. The shellac is the binder for the dust.

With egg whites instead of pumice you use 320 grit wet dry paper. Dip the paper in egg whites and sand just like you are French Polishing with pumice in a circular motion. The sand paper draws up saw dust and the egg white is the binder as you pack in the pores. The egg white drys glassy hard in a few hours. I let it go over night. THen sand back to wood and repeat as necessary.

Originally Posted by Frank Ford

Here it is, plain and simple. Rub hard and you generate some heat, which causes the alcohol to evaporate faster. During the finish building coats, it may or may not be appropriate to increase pressure for that reason. Once again, it's ALL about practice and experience.

You'll never catch me saying that by pressing harder you compact the molecules more tightly together!

In the final spiriting off, I'll often increase pressure as the finish begins to harden at the very surface. Remember, the full finish has already had time to dry thoroughly, and the spiriting off is analogous to buffing a lacquer finish. As I get to the very end, I'll drop the pad and use just the palm of my hand to rub increasingly faster and harder until my hand gets almost painfully hot. That process has the effect of glazing the surface to a very high shine, and takes only a short while, so I don't get stress and strain on the old joints.

Interesting. I have tried in the past to polish out an FP finish just like you would lacquer with compounds and buffers. It works fine but I've never gotten as good a finish as when I simply glaze it at the end and just leave it alone.

[rogthefrog]

Originally Posted by redir

Yes and no. Yes it is just the egg whites as they come right out of the shell but no you don't just paint it on. It's actually similar in principle as pumice and alcohol. With the traditional pumice method you first put a coat or two of shellac on the guitar. Then you load the pad with alcohol and a bit of pumice (there is absolutly no shellac used at this time). The pumice is an abrasive. As you swirl the pad around the alcohol dissolves the shellac and the pumice draws up saw dust which makes a slurry that gets packed into the pores. The shellac is the binder for the dust.

With egg whites instead of pumice you use 320 grit wet dry paper. Dip the paper in egg whites and sand just like you are French Polishing with pumice in a circular motion. The sand paper draws up saw dust and the egg white is the binder as you pack in the pores. The egg white drys glassy hard in a few hours. I let it go over night. THen sand back to wood and repeat as necessary.

Thanks for the explanation, that makes a lot of sense.