Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2006

Applying Polyerethane by Brush

Q. I recently primered a chassis with PPG dp90 non sanding epoxy primer. The parts are now back on the car where the plan was to hand brush the PPG Acrylic urathane paint over top the epoxy primer.

The problem I found was that the acrylic urathane is not meant to be brush applied. Is there an alternative paint that can be brush applied over the epoxy that will give the same strength as the acrylic urathane? I was considering a chassis paint made by bill hirsch that supposedly has synthetic resins in it, but was not sure of the compatability with the epoxy primer.

Is there something I can do to modify the acrylic urathane so that I can brush it with good results?

A. First, I have no idea what Bill Hirsch paint is and so cannot comment.

Acrylic polyurethanes are usually made for spray application, as you have already found out. If you want to brush the paint you would need to add some slow evaporating thinners such as a 50%/50% blend of lacquer thinners and butyl cellosolve. BUT, please be aware of at least the following:

1. I have not tried this myself and therefore don't know how it would work. You would need to experiment, and perhaps change the ratio of the blend to have more or less butyl cellosolve. Even then, you might find that the paint is not adequately brushable. I do not think that it will affect the performance of the coating, but I cannot guarantee this. Therefore, if you decide to add these thinners you are doing so at your own risk.

2. When you add thinners to a paint you are increasing the VOCs and HAPs and in doing so you might violate your local state air pollution regulations. Since I don't know where in the country you are located I don't know whether or not you are subject to such regulations. You should check with your local agency.

Another slow evaporating solvent that might do the trick is PCBTF which used to be sold under the trade name "Oxsol 100". You will not find this solvent readily available, and you might need to call paint companies or look on the Internet for someone who can sell you a small amount. Again, you will need to experiment to determine if it will work.

Best wishes,

Ron Joseph