Conversion Varnish as Primer Under Paint
Will a CV prime coat be compatible with latex paint? In this thread, pros advise against it. October 8, 2005
Question
My door supplier can prime (white only) my paint grade doors with an acid catalyzed conversion varnish. I normally spray latex for my paint grade doors. Will this work?
Forum Responses
(Finishing Forum)
I think you would have adhesion problems. I would ask them to spray a sample, same wood as the doors, and prep the same also, and run some test of your own. My feeling is that you will not get the bite you need from your latex.
From Paul Snyder, forum technical advisor:
When I do primer only jobs, I stopped using a catalyzed primer because of a complaint from an on-site painter that the paint wouldn't stick. I don't know what kind of paint they were using, but to avoid the problem, I switched to a single coat of pigmented shellac for that work.
Acrylics are known for their adhesion properties, so you may be okay as long as your paint is 100% acrylic and you scuff the primer before painting. Get a sample door from your supplier and paint it. Let it cure for a week or more and then do an adhesion test.
Testing is always a good idea. I would not recommend the system for exterior application. I have found CV primers and latex paints to be a good combination. Sand the primer with 180 grit or 220 grit sterated paper, tack off the dust and paint away. The latex has great surface adhesion to a clean, coarse film. You will get no chemical adhesion.
Don't depend on the sanding/scuffing to give you a better bond. If the sandpaper is too coarse, it will leave telescoping grooves; if it's too fine, it will do nothing. Sanding is basically done to remove any gloss, which has a slick surface that prevents adhesion.
I have heard (though not seen) acid catalysts causing latex to turn green. I think the pigmented shellac is a great choice, since it's basically inert after the solvents have evaporated, much like plain old lacquer.
