Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2005

Wash Primer Improves Paint Adhesion on Aluminum Extrusions

Q. We are a manufacturer of track lighting and have been painting our aluminum extrusion with a water-based acrylic bake paint. We have been pretreating the aluminum with a wash primer prior to topcoating. We have been advised by a paint manufacturer that it is not necessary to use the wash primer and we should apply their topcoat water-bake paint directly to the bare aluminum extrusion. Is this a good practice not to pretreat the aluminum or are we looking for paint failures by not using a wash primer?

Do you have any pretreatment at all? Do your extrusions go through an aqueous washer followed by a conversion coating, or do you simply take the raw extrusion and apply the wash primer?

If you are applying a conversion coating, such as Alodine, Chemfilm, or equivalent, then you do not need, and in fact should not apply a wash primer. In this case the wash primer would be a weakness in the system.

If you are coating untreated raw aluminum extrusions then a wash primer is better than nothing, but you MUST follow the application instructions exactly. Improper application of the wash primer can lead to failures.

If you are not pretreating the aluminum then in my opinion you are running a risk if you do not apply the wash primer. Before eliminating it, I suggest that you conduct extensive tests to confirm long term adhesion of the acrylic to the aluminum extrusions. I'm not suggesting that your vendor is incorrect, and I haven't seen the extrusions, but eliminating all forms of pretreatment can be dangerous. I am currently working on a law suite in which coatings are delaminating from aluminum, although in this case the aluminum is exposed outdoors in a humid environment.

Best wishes,

Ron Joseph