Laquer on Poly? - Woodworking Talk

ACP · 06-06-2009, 10:18 PM

Finishing is something that I am blindly stumbling forward learning and I was curious, can one put laquer over polyurethane? The reason I ask is I like the finish of laquer, but for my last project I decided to try polyurethane (oil base). If I wanted to change it to a laquer would I have to sand it all down and start over or could I just put the laquer over the poly coats? And while I am here, how long does it take spray can poly to dry usually? I am on day 3 and some parts, smaller areas actually, still felt tacky to touch. It didn't leave any marks, but it definitely didn't feel like the satin finish I was going for. Perhaps I applied too much in that area, but still, three days? Any help is appreciated.

kreuzie · 06-07-2009, 11:25 PM

Is this a nitrocellulose lacquer you want to apply over the poly? If so, the solvent will more than likely cause the poly to bubble (actually melting it). Try it in an inconspicuous spot, if possibe, or spray some poly on some scrap, let dry and then apply the lacquer to determine what will happen.

As to the undried poly, wait another day or two; if it's still not dry, scrape or sand the excess and wipe with mineral spirits.

kreuzie

ACP · 06-08-2009, 08:14 AM

Not sure if it's nitrocellulose but I will do your suggestion of a test scrap and see what I get. I will probably just sand the spots giving me trouble and re-spray them. Thanks Kreuzie.

Extbubble · 06-08-2009, 06:08 PM

I don't know if this is any help, but I bought some Thompsons this weekend to stain my deck, and they are giving 4 bucks back for every gallon purchased. http://www.thompsonswaterseal.com/ne.../deck_days.cfm It made the hard work more bareable.

Rick Mosher · 06-08-2009, 09:17 PM

The lacquer will probably wrinkle the poly. There are ways to seal it off and make it work but you could have adhesion issues. The best bet would be to take the poly off all the way and redo with lacquer especially since you are having drying problems.

kreuzie · 06-09-2009, 01:50 PM

Does it have that "lacquer" smell to it? (Smells like a body shop). If so, it's nitrocellulose.

kreuzie

ACP · 06-09-2009, 08:38 PM

They say you learn something new every day. I think this site ups that for me to like 10-15 new things a day. I did not know that about laquer and it does have that smell, so that settles the nitrocellulose question and I think I will just have to accept the finish. It has improved after a few more days and is no longer tacky. I did run a 1000 grit sponge pad over it to make sure there was no dust in the finish and a lighter colored spot develop in it, like there was glue on it (there wasn't) so I have screwed it up a different way. It is just a small spot, smaller than a dime, but it is driving me nuts. So now I have to ask, can I apply a touch up of stain on top of poly? Oil based on oil based?

BarslashJ · 06-10-2009, 06:59 PM

This is just a suggestion you may try. There is a product called Crystalac. It is available only at a few places. Online, Mcfeely's has it. Anyway, it is a water-born laquer. You can apply it over almost any finish after letting that finish dry for 72 hrs. I say almost because obviously waxed surfaces don't allow anything to stick to it. If your poly finish is still being a pain, you might try this right over the top. Scuff the finish with 320 sandpaper before using the Crystalac.

jgroover · 06-22-2009, 05:35 PM

I had the same question just the other day. You can put lacquer over poly, but you need a barrier coat in between. The barrier has to be wax free shellac. I picked some Zinsser brand up today actually. Going to try it tonight.

Supposedly that barrier coat will protect the poly from being harmed.

curtis · 07-09-2009, 02:02 PM

Sorry to put in another question, but I've been following this thread with some interest.
Is it true, then, that there is no problem with laying shellac down over poly?

**Leo G** · 07-09-2009, 05:23 PM

There is a problem with putting lacquer over poly. It will be an adhesion problem. You need to put a barrier coat in between the two. The lacquer will not bubble the poly. You can either use a vinyl sealer or dewaxed shellac as the barrier coat.

Rick Mosher · 07-09-2009, 07:02 PM

Lacquer will definitely wrinkle poly if the poly is a fresh enough coat. Poly that has cured will be safer. The adhesion has more to do with the grit you are sanding with. (mechanical bond)

cabinetman · 07-09-2009, 09:14 PM

Quote:

Originally Posted by Rick Mosher

Lacquer will definitely wrinkle poly if the poly is a fresh enough coat. Poly that has cured will be safer. The adhesion has more to do with the grit you are sanding with. (mechanical bond)

I agree with Rick. It's not an adhesion problem, because the base for lacquer is lacquer thinner (which by the way is an acetone base). Both lacquer thinner and acetone will dissolve vinyl sealer, and shellac.

Lacquer over oil base can wrinkle (disfigure) the finish, maybe not immediately, but it could happen over time. Other physical properties affecting compliance is each of the film finishes can expand and contract at different rates. This in will present itself as an obvious failure. I've tried combined finishes and resign myself to stick with compatible chemistry.

My suggestion is to strip the oil base off, or, continue with the oil base until you're satisfied.