Can I Spray Nitrocellulose Lacquer over Waterborne Lacquer?

A touch-up and repair problem brings on a discussion of finish compatibility issues, yellowing, burn-in, and more. July 3, 2008

Question
I have a piece that was sprayed with Target water-based lacquer but has some damage needing re-spraying. Can it be top-coated with NC lacquer? Will it need a sealer coat of some sort in between?

Forum Responses
(Finishing Forum)
From contributor C:
Is the Target product an acrylic finish or a co-polymer combo such as a piggyback resin - polyurethane/acrylic or other? Does it have a catalyst to it or not? How fresh or old is the target coating?



From the original questioner:
It is acrylic, no catalyst and is about 3 years old.


From contributor C:
I forgot to ask if this is a stand-alone item or a piece of a larger piece such as cabinet doors, etc? The reason I ask is because if you use nitro over acrylic it will turn yellow in time - how long? That depends on the amount of light it is receiving on the surface. Regardless it will turn yellow - if this is a problem for what your repairing then I would not go with nitro over the acrylic. Can it be done Ė yes. Should it be done - not really.

Lacquer solvents vary some from acrylic solvents and may cause reaction problems if they donít youíre still applying a coating that has different expansion parameters to a degree and it could end up cracking later down the line. The lacquer is capable of solving the shellac and becoming attached well with the acrylic but I would still advise against it unless you feel you have absolutely no other choice

Are you saying you have no acrylic to use over the necessary repairs? Mohawk sells plenty of acrylic spray bombs you can buy and keep on hand for patch work or bulk for total recoat and of course if you know what type of acrylic it is you can use target. I'm wondering why youíre even thinking of using nitro over Target if you know that?



From contributor W:
Yes, you can apply nitro lacquer over Target USL. Clean the USL with denatured alcohol, fine sand with 400 grit and then apply your fresh lacquer.


From the original questioner:
The piece is a small cabinet with multiple surfaces that need some burn in repairs and a couple small dents repaired. I haven't done much WB work so was hoping to avoid a new learning curve for one small piece. Yellowing would not be a good thing, especially if it occurs several years from now. How yellow are we talking though and could it be prevented with a sealer coat between? If so what would be my best bet for a sealer?


From contributor C:
You donít need to use water base acrylic, solvent base will work just fine. Can you get Mowhawk products where you are? The yellowing will be quite noticeable in several years or even sooner. In fact if itís an amber color in the can it will be visible immediately. Even if it is so called water- white it will amber out pretty quickly. Within months it will start to be noticeable. Mohawk has several sheens of acrylic cans for touch up/repair use.


From contributor C:
As to the sealer coat between - if you mean as a barrier to prevent incompatibility problems there arenít any that I know of that are readily available. Shellac will not work because it too is amber/yellow to begin with and the isolation coats used in conservation are both costly and special order items. Try to stick with solvent base acrylic, even if you have to buy it at Home Depot or another place.


From contributor E:
To the original questioner: You should try using Targets Usl on this. It applies easily. The learning curve is quite simple and short. If you are worried about what happens when using NC Lacquer then the time spent learning Usl application looks even better. It should also be noted that Usl also straws in color over time also unless itís coated with a super clear polyurethane.


From contributor P:
If you can spray solvent based lacquer well, you can spray Target's waterborne finishes. There's no "learning curve" to be concerned with.


From the original questioner:
Thanks for all the help guys and the quick responses as well. I think I am going to strip the main surface to do some repairs then can shoot NC over the entire area without layering over WB. A couple small spots will need touched up in other areas and the acrylic spray bomb sounds like the best bet for compatibility. I found out that this particular piece was shot with Target Ultima Acrylic WB Lacquer and it appears to have yellowed quite a bit in three years. It has been in storage for about a year and a half so it wasn't UV that made it yellow, just for future reference.


From contributor V:
In case you haven't stripped it yet, I'd point out that Target Oxford Ultima Spray Lacquer (USL) has 100% burn-in capability, even in a cured finish. So if you repair with the same material it will blend in very well. The product has a light straw color and is not as clear as the other products in the Target line, but really does not cause a problem when clear-coating over a colored finish. Itís very forgiving to spray also, with a quick recoat time. The only thing is it will lift water based dye unless you lock it in with a mist coat or a shellac barrier coat.