Applying Pre-Catalyzed Lacquer over a Tung Oil Wash-Coat

A light coat of thinned oil finish can work as a wash coat under precatalyzed lacquer, but there might be better alternatives. September 16, 2008

Would there be any problem spraying pre-cat lacquer over tung oil (used as pre-stain conditioner) then stained wood surface? I have found on soft woods this works best to prevent blotching, but usually put on another coat or two of oil for final coat.

Forum Responses
(Finishing Forum)
From contributor A:
Shellac has been the traditional sealer for preventing blotching. I would have adhesion concerns with the tung oil.

From contributor P:
As long as you don't apply enough of the tung oil to develop a film finish over the wood, there should not be any problem. With one coat of the tung oil, most of it will soak into the surface of the wood. With added coats of the oil, it will build up on the surface. Drying oils produce a relatively soft/flexible film and lacquer is a hard (brittle) finish. Using a brittle finish over a soft finish leads to cracks in the topcoats.

From contributor L:
I would think using a mixture of tung oil whacked in half with naphtha would give the result you are looking for, but shellac offers more in the way of magnification, pack out and good sanding. That is, a diluted mix of shellac.

From contributor R:
Could you tell us a little bit more about the project you're interested in working on? Various oils can cause problems for a coating, be it a post-cat or a pre-cat. There might be better alternatives for you when it comes to a stain conditioner.

From contributor D:
Some tung oils are nothing more than varnish, linseed oil and mineral spirits. Some tung oils are real tung oil. From the way I read your application, if you lay down a thinned coating of vinyl sealer, you shouldn't have any issues down the road as long as you are mindful of what contributor P wrote about using the so-called tung oil as a film-forming finish. Your use of the product is what used to be called an oil sealer, which, because of its penetrating nature, seemed to bring out depth and chatoyancy in some woods.

From contributor R:
I used this for some oil finished pieces and like the way it works. I have used other wash coats as some suggested, but it seems with this kind of wash coat, they either seal too much or not enough? The tung oil or Danish oil seemed to work great. I have been tempted to try it under the lacquer, but like most of you, I'm a little scared to do it!

From contributor P:
The tung oil will work fine as a washcoat. Many stains contain linseed oil, which is very similar to tung oil. With pre-catalyzed lacquer I usually use vinyl sealer for the washcoat. It has similar properties to shellac as far as good adhesion, moisture resistance, and a barrier coat for glazes. And you can usually get it from the same supplier where you get the lacquer. But lacquer (including pre- and post-catalyzed) also makes a good washcoat if you thin it properly. You could simply take a small portion of the lacquer and thin it until it's about 10% solids by volume and spray one light wet coat. Let it dry and scuff sand very lightly to smooth before applying the stain.

From contributor D:
When using pre and post cat finishes with Danish oil (which is also nothing other than a mix of varnish, linseed oil and mineral spirits) you should use vinyl sealer as a barrier coat. There's always the possibility of the acid catalysts reacting with the metallic driers (japan drier) that are used in these oil finishes. The effects could be an unwanted color shift.