I'm having this debate about urethane products and lacquer or enamel paints. So as we all know base coat and clear coat are acrylic urethane. However acrylic urethane does not melt into former coats, which means it has the tendency to delaminate as it ages. That means that clear coat does not melt into the former coats of base urethane like lacquer paints, which overtime causes the topcoat to peel off. So my question is, can you do spot repairs on single stage urethane like on lacquer or is single stage acrylic urethane just like base/clear urethane. My worry is that just like bc/cc, single stage urethane overtime would be able to delaminate from the top coat. I'm confused as to what causes chemically causes bc/cc to delaminate. From my understanding, lacquer and enamel do not act chemically in the same way urethane paints do.
I'm not a professional painter. But i had a section of my single stage lift. Went to the car wash and a small rock chip became a pie pan area of no paint. I feathered the edge and re shot the panel. it looks great and has held up for 2 years now.
I found out the answer. So urethane base is air dry like lacquer which means it never cures. Clear is a chemical cure urethane which is why you bake it to dry your paint job faster, and lacquer and urethane are not compatible. So they have an optional binder in the mixing base that makes it somewhat compatible, but adding hardener to base coat does not actually cure it. So when clear fails it can separate from the base coat. They are two different chemical structures. That is the only reason why clear peels away. Clear fails overtime by buffing it too thin or from daily abuse, and then your UV protection is gone. Since base coat has no UV protection or chemical catalyst structure it becomes chalky since it never hardens. Then your clear has nothing to bond to anymore and it separates as it ages. So let's talk about single stage. All single stage paints are one chemical structure. So with lacquer you want to use lacquer primer which is air dry. Then you have single stage acrylic enamels and acrylic urethanes. They are both catalyst paints. Single stage paint is a chemical cure urethane like clear, so if you paint with single stage urethane you are going to want a primer with a catalyst that dries by baking it (which is almost all primers these days). Then you have one chemical structure and there is nothing to delaminate at all. Currently to my knowledge there is no base coat on the market that dries with a catalyst. There are no bodyshops out there who are baking base coat. I'm glad I figured this out.
My experience after many years in the body biz..... Never paint any urethane over lacquer primer. It will bubble or peel eventually. No real reason to use lacquer primer anyway. Paint products adhere by chemical or mechanical bond, or sometimes both. This is why it is best not to mix and match systems or brands. Most base coats are able to be catalyzed.
You can use single stage as base cote under clear cote, and you can use epoxy primer under lacquer paints.......
My paint rep got me to using a catalyst in my basecoat a few years back and it has eliminated a few problems. I just add about half as much as the clear requires, using the same catalyst as the clear. So if the clear is 4 parts clear to 1 part catalyst, just mix the basecoat 8:1.
The reason for delamination older clears I've seen described that makes most sense to me is this: Base coats had no UV protective ingredients and relied on the clear for that. The UV protection in the clears was inadequate to protect the base coat from degradation. The base fails causing the clear to lose adhesion. I have had 2 clear failures on stuff I've sprayed. Both involved base and clears from different makers. Never again. From now on the base and clear will come from the same maker, unless the clear source can ***ure me that it will work with the base I've got. Google 'crosslinked paint' for more info that you'll ever need.
The Jalopy Journal
