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So- I finished spraying the shellac on the guitar and let it cure for 24 hours in a room with controlled humidity and temperature (49% RH, 70-78 degrees). Several times now I have sanded the body up through 4000grit with micro mesh, been happy with the way it looks then returned the next day to find that the shellac had picked up the texture of the fabric it is resting on. The shellac polishes up well, doesn't feel sticky to the touch and I don't leave lasting fingerprints in it when I handle it. I tried changing the fabric out thinking it might have chemicals in it that are affecting the shellac, but the same thing happened on a fresh, plain cotton shirt. Even the pressure of sanding will push it into the fabric enough to make a mark.

Was the shellac bad? Do I just need another surface to rest it on (currently on a cotton tee shirt on top of two layers of cardboard on top of a foam cupboard liner.

The pore fill was gypsum compound died black, covered with a few wash coats of shellac. The body coats were sprayed on with a turbine driven HVLP gun. The first few sprayed coats of shellac were tinted with ColorTone liquid stain. The final coats were sprayed with a 1.5# cut of superblonde shellac made from flakes. I've never sprayed anything else through the gun I used, so I don't think it was contaminated there, if that's the problem. The shellac was all newly mixed, not old from sitting around.

Thoughts or suggestions appreciated.

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Registered Architect (Texas, New York)
LEED AP

I've had this same issue, but with Varnish. It eventually hardens up (like after 2-6 months) and will stop taking impressions from your jeans, the case fabric, what have you...

I know you're doing shellac, but maybe it's a similar issue. What made my finishes get hard faster was (I think) to use zero turpentine (which I had been using a bit of) and as little acetone to thin as I can get by with (about 2/3 of the original amount I has been using).

I have NO idea why turp or acetone would cause varnish to set soft and harden slower, but I reduced those thinners, and my finishes seem to harden better and faster.

Are you using either of these solvents? Probably not...alcohol and shellac?

This may be a very stupid question, but why don't you hang the guitar, instead of resting it on anything at all?

That's one of the benefits of French polish over spraying shellac. You'll have to wait it out, similar to lacquer.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

That's not a stupid question. But I have to sand it. And when I am sanding (say) the top, the back is resting on the cloth and when I finish the top and turn it over the back has new impressions from contact with the cloth - probably the downward pressure of sanding is contributing to the problem in this case. So I tried standing it on end, and the then the side picks up an impression ....and so on.

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Registered Architect (Texas, New York)
LEED AP

Well - that's actually good to hear. I mind waiting much less than I mind sanding off the finish and starting over! have you had that problem when spraying alcohol/shellac finishes?

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Registered Architect (Texas, New York)
LEED AP

Turpentine slows the drying process in varnishes, while paint thinner will flash off quicker when used to thin varnish, and thus dry faster.


Alex

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"Indecision is the key to flexibility" .... Bumper sticker

I don't quite see what the difference between spraying or padding the shellac onto the surface but am always open to learn. Either way I think it needs to cure for more than 24 hours.

Fred

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Fred Tellier
http://www.fetellierguitars.com
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French polshed shellac is a bit harder than sprayed shellac right away, but it still really needs at least a week to be nice and hard - two would be better. I have taken guitars to a show that I just finished, and I have to take the materials with me to touch things up after putting the guitars on a stand. Always leaves a mark on the back. Polishes right out, but always a mark on a fresh FP finish. After a couple of weeks - no mark.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Depends on your technique. I pummel my FP rather than spirit and stiff, makes it tough, tight and hard very quickly. Ever hear the phrase " give him a good shellacing"? That's because it sounds like someone pounding a speedbag when you do it. That's the way it was handed down through my family, Uncle Mel didn't call it French Polish though, it was just shellac, padded on.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

'Splan pummeling to me, please!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Yeah, comon' give over the secret to pummeling.....better NOT be what I used to get after junior high school......

It's softer because spraying/brushing is nearly always put on much thicker than when padding. Give it time, it will eventually harden so that the imprint does not happen. I polish with the Neck clamped into a Parrot Vice, none of the body surfaces come into contact with anything.

Here is a link to a video of a presentation I did last year on my FP technique. Not the best quality but I explain my method which is different from most everyone else's.

http://www.youtube.com/watch?v=aJ5Zmm9ZKvc

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

That's a really beautiful workspace you have there, Brian!

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Registered Architect (Texas, New York)
LEED AP

I have had the same issue with lacquer. I just leave more time for it to dry now before buffing. I also scuff the surface once or twice a day to help open it up and allow the solvents to gas off. It seems to help. I don't think it would work with shellac.
The scuffing is done with the same block I will be leveling with, so I sort of kill two birds with one stone. I am speeing up the dry time, and doing a little leveling each day. Since I brush my lacquer, there is a lot more sanding to be done versus spraying the lacquer. Before I knew this about lacquer, I thought I had a bad batch of the stuff. But, adding 2-3 more weeks to my drying time has pretty much ended the issue.

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http://www.CostaGuitars.com
PMoMC

I wish it was mine! That was done at a mid Atlantic luthiers meeting at a co op called the goggle works. You rent time and space there.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

well crud. Shelf collapsed today - unfortunately I had moved the guitar to a bench below it to get it out of the way while I cleared out the finishing supplies and equipment on the main bench. Wood, boxes, all sorts of things fell onto the guitar. It will be playable, but it won't ever be pretty. Couple a good chunks, major 3" gash in the wood at the end graft. ugh.

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Registered Architect (Texas, New York)
LEED AP

Ouch.

Brian, thanks very much for the link to your presentation! I appreciate your detailed description of your process, and of the reasoning behind it. I'd never heard anyone suggest there were benefits of leaving the wax in the shellac, though it's often said that button lac produces the most durable finish. I've only finished one guitar with shellac, but I enjoyed it and liked the finish, except for its lack of durability. I'm definitely going to experiment with some changes in my French polishing process.

A minor side point: You might be interested in knowing that your explanation of the use of "shellacking" to mean "pummeling" is, as far as I can tell, unique. I checked my OED, and then hunted around on line in some other dictionaries, but nowhere could I find the idea that the process of applying shellac was like punching so gave rise to the slang usage of shellacking. Your explanation sounds more plausible than any of the ones I found.

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Tim Allen
"Never hurry, never rest."

Roberto,
Dang, that sucks. Is this the all HOG guitar you've been working on?

That's the one. It does stink, but it was just pure bad luck - moved it for a few minutes while rearranging something else and a shelf happened to collapse at that moment. Just plain ol' bad luck. So I will use this guitar to experiment with a distressed/worn finish, I guess.

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Registered Architect (Texas, New York)
LEED AP

Mate, call it "relic'd" and slap an extra $2K on the price tag...

Thanks for the great tutorial! How would you pummel the finish of a guitar though? From what you show on the test panel, it looks like you are hitting it quite hard. Wouldn't that crack the top?

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

https://www.facebook.com/FenskeGuitars

LOL. Yeah, believe me I'd love to - but I couldn't sell it in good conscience. (I know you are joking.) That's alright, at least this was a project for me and there's no client sitting around waiting for their guitar.

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Registered Architect (Texas, New York)
LEED AP