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| Help with shellac finish http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=52075 |
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| Author: | Heath Blair [ Sat Jun 22, 2019 2:37 pm ] |
| Post subject: | Help with shellac finish |
Is finishing the* most frustrating part of building? Yes. Yes, it is. Have I had issues with every* step on this build? Yes. Yes, I have. I’m building a soprano uke and I’m having trouble with the shellac finish. The shellac is staying relatively soft. A thumb left on the surface for a few seconds will leave a light imprint. The wood is mango. No pore-fill. Straight Zinsser SealCoat shellac. Can is brand new. Lot code is SS 1111, though I can’t figure out what that means. Shellac has dried for two days. I’m applying the shellac in a French polish style with a muneca. 2 lb. cut straight from the can. A dab of olive oil on the muneca occasionally, but I’ve found it mostly unnecessary. Finish looks decent* after spiriting off. This is my first attempt at an all shellac French polish style finish. There are moments where I think, this is the worst, I’ll never do this again and moments where I go, hey, this is actually pretty great. I leveled and polished through the grits on the back and the finish was just about where I’d like it. I know those with more experience, don’t need to sand, but I did. Then I started noticing the finger prints left in the finish. What gives? Heart-broken, Heath |
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| Author: | Eric Reid [ Sat Jun 22, 2019 2:49 pm ] |
| Post subject: | Re: Help with shellac finish |
Stop adding finish. Let it dry for a week, and see if it has hardened up. If it still prints after two weeks, you'll need to sand back heavily--back to wood would be best--and start over. The problem comes from building the finish too quickly. Keep the shellac well thinned (viscosity like water), and apply very thin coats with at least three hours between sessions. If you build the finish too quickly, it can take years to dry. |
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| Author: | TRein [ Sat Jun 22, 2019 3:21 pm ] |
| Post subject: | Re: Help with shellac finish |
I had somewhat similar results with Sealcoat. It was a fresh, unopened can and while it appeared to dry OK it did imprint readily even after 6 mo. Stripped it off with alcohol and refinished with flake shellac with no issues. I for one don't buy the statement that Sealcoat is identical to flake shellac. If the uke were mine I'd strip the Sealcoat off (which should be easy to do) and start over with freshly prepared flake shellac. Sanding the offending Sealcoat should not be necessary. Straight alcohol should do it. |
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| Author: | Dave Livermore [ Sun Jun 30, 2019 10:22 am ] |
| Post subject: | Re: Help with shellac finish |
this could be several issues affecting your results. First thing to check is the age of the shellac. Shelf life is a real thing. Even if it is an un-opened new to you can, it could have sat on the shelf at the hardware store for quite some time before you got it. Second, as has been pointed out is the thickness of your application. Try cutting that 2lb cut down to .75 or thereabouts. Third, note that the difference between wiping on shellac vs french polish is from the pressure you use when applying. The swirl action, and the proper shellac, polymerize the finish and meld it a hard, protective film. Lastly, go easy on the lube. Less is better. Heck, if you’re not going to shoot something else over the shellac, try real shellac next time (it has wax in it, which is a natural lubricant for the application. Start your sessions without lube. When you start to feel the rag starting to drag, then and only then, and a drop of oil. Hope this info helps, dave |
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| Author: | jfmckenna [ Sun Jun 30, 2019 11:49 am ] |
| Post subject: | Re: Help with shellac finish |
I know people use and say good things about Zinser but I would not use it. I have used it on furniture and it seemed fine but you risk buying anything in a can because of it's age and so on as Dave stated. It's real easy to just get some buttons or flake shellac, add alcohol and make your own. I can't imagine doing an FP finish and not using a lubricant oil. Again, some people do it, I don't know how. I use the John Greven method of mixing pure walnut oil in with the shellac which essentially becomes part of the finish as well as acting as a lubricant. With normal shellac I do sessions every 2 hours. So it should dry pretty fast, if it doesn't then there is something wrong with the mixture. Sanding is pretty normal even for expert finishers. Sometimes you get some funky buildup, usually a swirl, but sometimes dust or cat hair or something and it needs to be sanded out. |
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| Author: | SteveSmith [ Sun Jun 30, 2019 12:08 pm ] |
| Post subject: | Re: Help with shellac finish |
I use Zinsers but only for temporary protection, usually on tops. It works fine but I always sand it off before finishing. |
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| Author: | B. Howard [ Mon Jul 01, 2019 6:18 am ] |
| Post subject: | Re: Help with shellac finish |
Not enough pressure when applying and likely applying too thick. Seal coat would be my last choice for FP..... Here is a video where I describe my process. https://howardguitars.blogspot.com/2015/09/french-polish-finishing-traditional-way.html |
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