I am nearly now finishing a walnut/ cherry box with shellac over tung oil (Frenchy saved me from the dark side). The oil was thinned 60/40 spirits to oil. My question is: does the tung oil have to be completly 100% cured before applying the shellac? Jeff Jewitt’s book says “let oil dry at least over night” before applying shellac. I have also read (but can’t seem to find it again) that oil has no problem curing under shellac. Having not done this before, I though I would ask the more experenced.
Thanks,
KB
BTW Rich14, what kind of grain filler do you use? I read your post in another thread: “I for one, do not use shellac to fill imperfections or to fill the grain. If I want a glass smooth surface, I will first use a grain filler therefore I am working with an almost perfectly flat surface”
Replies
Keef, I would wait a week after applying the tung oil to seal it with shellac, but that's probably being a bit over-cautious. The tung has probably gotten all the exposure to Oxygen it needs during the application process, and will polymerize, eventually, no matter what. But why rush? I never hurry the finishing process. It's the wrong time to cut corners. I use a solvent-based silex (silica) filler, such as Behlen Pore-O-Pac. I've never used a water-based filler. Probably never will.
This was supposed to be a Christmas present, so waiting an extra week isn't going to kill me. I had to make the lid 3 times to get it really right- time well spent I must say. Lacquer over shellac on the test pieces looked really-really good (you remember my lacquer question a few weeks ago). Of course, the shellac by itself looked really good too. I did not, however, test using the tung oil. Thanks Rich, I will wait.
KB
Oh, good timing. I'm just finishing up a box too. Black Walnut box, Amboyna lid with Macassar Ebony trim on both as well as some Amboyna trim on the box. I just put on a coat of Walnut Oil early this afternoon. This is my first time using it. I like the warmness it lends the woods. Frenchy has inspired me to try his ultra-thinned approach to Shellac which I'll apply tomorrow afternoon.
The rule of thumb with "drying" oils is to give them a minimum of 24 hours. Longer doesn't hurt, but less is asking for trouble a few months down the road. If the oil isn't cured then it's got nothing better to do then attack the bond between your top coat and the wood.
Edited 2/12/2007 2:22 am ET by Kevin
Was what you used labeled pure tung oil or 100% pure tung oil? If either of those terms don't appear the material can be just about anything. Some Tung Oil Finishes are varnishes, some are oil/varnish mixes and in either case the percentage of tung oil as an ingredient can be very minor. For example, Minwax Tung Oil Finish is an oil/varnish mix, while Formby's is a varnish. Either type will be OK under shellac and probably will cure more reliably overnight than pure tung oil. With pure tung oil overnight is cutting it a bit close, especially if your finishing space isn't heated to around 70° F.
Good point, Steve. The finishing industry labels just about ANYTHING that can be applied as a rub-on finish as, "tung oil." They even package the same product otherwise labeled as a "rub-on varnish" also as "tung oil." Same formula, different labels. Wonderful practices. Ironically, such products, labeled as tung oil, usually have NO actuall tung oil in them. They MAY have some, but if they have any oil, despite the label, it is mostly linseed. But even that is doubtful. The only product you can be sure about is one labeled, "pure tung oil." Then, you should be sure it says "polymerized" or "partially-polymerized" tung oil. Tung oil which has not been at least partially polymerized is among the slowest of oils to harden, taking many months, if not forever! Rich
Thanks fellas. Just for the record, the TO I'm using is "fresh" and 100% pure. I posted another thread "Tung Oil Drying Time" so maybe I can figure out a few mysteries of this drying deal.
KB
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