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Shellack over tru oil?
http://www-.luthiersforum.com/forum/viewtopic.php?f=10101&t=44098		 Page 1 of 1
Author:  fingerstyle1978 [ Thu Sep 04, 2014 11:48 pm ]
Post subject:  Shellack over tru oil?
So I pore filled with Shellack and then finished with tru oil. But tru oil dries very thin and I am using micro mesh to polish it.

Long story short, I went through in a few places on the neck and refinished with tru oil (preferred finish for the neck) and there are a couple spots on the body that I am worried about the same. I'm wondering if I should just sand it off and re-do in shellack, or if the existing (thin) layer of tru oil would take shellack over it.
Author:  meddlingfool [ Fri Sep 05, 2014 12:17 am ]
Post subject:  Re: Shellack over tru oil?
Wouldn't it be better to put on more tru oil?
Author:  fingerstyle1978 [ Fri Sep 05, 2014 1:14 am ]
Post subject:  Re: Shellack over tru oil?
For the neck yes, but I'm considering just stripping everything off the body as I think true oil is nice as thin as it is, but it's probably very hard to get a gloss finish without like 20+ coats.

I don't know though, I just know it dries thin- which is great for a neck but the body isn't even close to being done with the micro mesh (3200/12,000 grit) and it's already showing through in a couple places after 12+ coats.
Author:  Michael.N. [ Fri Sep 05, 2014 5:44 am ]
Post subject:  Re: Shellack over tru oil?
Putting Shellac over Tru Oil may not be a great idea. It's almost certain that Shellac is harder and more brittle than Tru Oil, so effectively you have a hard material sitting on top of a soft material. The softer underlying material moves and cracks the harder overlying shellac. You may get away with it but there certainly is a fair chance of it crazing. The rule is that you go from lean to fat, not fat to lean.
Not only that but if you sand through (in certain areas) the Shellac will give a different colour to the tru oil. Oil finishes tend to give a darker finish. It may end up looking patchy.
It's fine to go the other way though - shellac first with Tru Oil on top, lean to fat.
Having said that I often do a single coat of a thin Oil finish and Shellac over that. The Oil pops the grain better than Shellac. But it's just the one single very thin coat and I make sure the that the coat is very dry by placing it in a UV cabinet.
Author:  Haans [ Fri Sep 05, 2014 7:10 am ]
Post subject:  Re: Shellack over tru oil?
One of the cardinal rules of finishing is not to mix finishes.
Author:  RusRob [ Fri Sep 05, 2014 8:44 am ]
Post subject:  Re: Shellack over tru oil?
Haans wrote:
One of the cardinal rules of finishing is not to mix finishes.


+1 Haans

I think people are only asking for problems by mixing different finish materials. Even using the same product by a different manufacture can cause adhesion problems or other issues like crazing or checking.

If I do an oil finish and want closed grain then I sand the wood using oil until it is filled and smooth. If doing a French Polish I use shellac and pumice until the grain is filled. But never mix the two.

But Hey... To each his own [:Y:]

Cheers
Bob
Author:  Michael.N. [ Fri Sep 05, 2014 8:59 am ]
Post subject:  Re: Shellack over tru oil?
Mixing finishes isn't a problem. It's only a problem when you are unaware of the right techniques and the pitfalls.
Early methods of French Polishing were Shellac done over a ground of Linseed Oil. It works and is detailed in all the old books on finishing. I've done the Oil sand fill on many French Polished Guitars. In fact that method is my standard type of finish for the Back/sides.
Author:  Lonnie J Barber [ Fri Sep 05, 2014 9:25 am ]
Post subject:  Shellack over tru oil?
I use shellac to protect the wood(especially topwood) then a good sand not going to bare wood but trying to leave the pores filled. Then begin applying Tru-oil over this tiny amount of shellac. I really don't call what I do mixing my finishes. If you get technical I guess I am. But I do apply lots of coats. About the fifteenth coat I get really tired of doing it. I've not really used micro mesh before but plan on it on my current build. Hoping not to sand through. If I do I'll just stop sanding so much.


Sent from my iPhone using Tapatalk
Author:  SteveSmith [ Fri Sep 05, 2014 10:12 am ]
Post subject:  Re: Shellack over tru oil?
Tru oil is fine over shellac. I have not tried it the other way around.
Author:  Rodger Knox [ Fri Sep 05, 2014 12:03 pm ]
Post subject:  Re: Shellack over tru oil?
fingerstyle1978 wrote:
So I pore filled with Shellack and then finished with tru oil. But tru oil dries very thin and I am using micro mesh to polish it.

Long story short, I went through in a few places on the neck and refinished with tru oil (preferred finish for the neck) and there are a couple spots on the body that I am worried about the same. I'm wondering if I should just sand it off and re-do in shellack, or if the existing (thin) layer of tru oil would take shellack over it.


TruOil is different than spraying lacquer, and I've had pretty good results with this technique.
Don't try to build up enough thickness to go through the grits after it's cured, go through the grits with your sanding between coats. This is dry sanding only, if you wet sand TruOil, you're asking for witness lines.
Every on 3 or 4 coats, let it dry 24 hours and sand out all the shiny spots, working your way through the grits from 600 to 1000. That is, 3 or 4 coats and sand with 600, 3 or 4 more coats and sand with 800, etc. If you sand through it's no problem, you're putting on more coats anyway.
Warm the oil for the final few coats, and get it on really thin and smooth. Let it cure for a month and you're done.
Author:  RusRob [ Fri Sep 05, 2014 12:38 pm ]
Post subject:  Re: Shellack over tru oil?
Like I said:

RusRob wrote:
But Hey... To each his own [:Y:]


I have been finishing wood and metal the better part of my 60 years and have seen enough failures in finishes that have learned not to mix finishes.

I wasn't saying you can't do it. That was just my opinion. just like it is your opionon that you can.

Quote:
Early methods of French Polishing were Shellac done over a ground of Linseed Oil.


I think you will find that it was raw Linseed Oil which is a non drying oil (as opposed to Boiled Linseed Oil). It was common to apply Mineral oil, Olive oil, or Raw Linseed oil directly to the wood first but it is usually the same oil that they are using in the French Polishing process.

True Oil on the other is polymerized and has a lot of additives in it to help it dry so it isn't an actual oil that would be used in the FP process.

Bob
Author:  Michael.N. [ Fri Sep 05, 2014 1:45 pm ]
Post subject:  Re: Shellack over tru oil?
Raw Linseed Oil is a drying Oil, slow but a drying Oil for sure. Once you apply it directly on to wood you aren't going to remove it by putting Shellac on top. You may remove some, it may provide lubrication but once it's soaked into the wood it's pretty much there forever.
Anyway, mixing finishes isn't just a matter of opinion. It's perfectly possible and safe to do so - providing you know how to do it.
Author:  RusRob [ Fri Sep 05, 2014 2:03 pm ]
Post subject:  Re: Shellack over tru oil?
OK....

I guess you must be right....

Thanks for correcting my ignorance.


Cheers,
Bob
Author:  dzsmith [ Fri Sep 05, 2014 6:25 pm ]
Post subject:  Re: Shellack over tru oil?
I'm using truoil for the first time.
I am amazed at how good it looks on Sapele, Maple, and Mesquite.
I would not put a hard finish over a soft finish as Michael N. suggested.
I did discover that truoil can be removed with alcohol (not intentionally).
Author:  ballbanjos [ Fri Sep 05, 2014 6:59 pm ]
Post subject:  Re: Shellack over tru oil?
I have French polished shellac over Tru Oil many times over curly maple for many years without any problems. In fact, over figured maple, it's been my standard and I have quite a few banjos out there that have seen heavy festival use with finishes that still look good 10 or 15 years later using this finish. I use a very thin Tru Oil base, which pops the curl very nicely--better than the shellac does IMHO. Let it dry a day or so, and shellac has had no problems sticking and staying stuck from what I have seen.

On oily woods, however, this might well not be the case. I've had trouble with Tru Oil hardening over certain rosewoods, cocobolo, etc. Shellac over a not-hard Tru Oil base would not be a pretty sight....But over figured maple, it's really nice. I've used it on mahogany, walnut and other woods too without any problems.


Dave
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