Expert: Eileen Cronk - 2/11/2009

Question
Can you give me a brief overview of compatibility between lacquer and urethane?  Can one go over the other and vice versa?  Also, how often is ambient moisture an issue in spraying lacquer?

Thanks

Answer
Hi Lee
Nice to hear from you.
One would think that because these products are mineral based that they would be compatible but its not always the case.
In my opinion, its not a good idea to apply lacquer over poly as the lacquer can actually eat the poly...but, I have done it successfully over an old poly finish.
Its also not a good idea to apply poly over lacquer but once again I have done it successfully.
Aside from eating the underlying finish as in lacquer over poly, the reasoning with poly over lacquer is an unstable finish.
And just to add to the confusion, I can tell you for absolute certain that you cannot apply lacquer over tung oil. It just cannot be done successfully. But I can tell you for certain that you absolutely can apply tung oil over lacquer.
So go figure LOL
Lee there is a whole lot of opinions on this subject and just for some reading for you I enclose this.
http://forum.doityourself.com/furniture-wood-cabinetry-finishing/260019-polyuret...
As you see the opinions are widely varied and perhaps there are no hard fast rules. I find we do whatever works for us.
With regards to ambient moisture and spraying lacquer there is no guess work.
Lacquer cannot be sprayed in high humidity or it will cloud guaranteed. The moisture is actually trapped in the lacquer as you spray.
Whenever I have to use lacquer I go by this rule.
The temperature must be over 65 degrees F and the humidity must be below 65 in the working area.
Which brings me to the reason I mentioned the tung oil over lacquer.
If you ever get cloudy spots applying lacquer, let it dry and then rub a tiny bit of tung oil over it with a rag. The cloud instantly disappears.
Hope this helps
Regards
Eileen