Replies

1. 
   BertJ | Jul 24, 2003 09:06pm | #1

   Lechel,

   Check out automotive finishes for fiberglass. One of the Dupont products (Imron Poly Enamel) is used extensively in painting aircraft and fiberglass yachts. It offers UV protection as well as excellent adhesion. Pricy but worth it.

   BJ

2. 
   Telemike | Jul 25, 2003 08:05am | #2

   The first step is to figure out what the skin on the door is.  Is it vinyl, is it polyester fiberglass, or something else?

   That said, clean and rough up the surface really well by washing then sanding or sandblasting.  The physical roughness may give you  most of your adhesion.

   Then go to a marine supplier and use a marine paint with the appropriate primer - ask the guy at the counter; if you're lucky, he'll actually know what he's talking about.

   PS:  If it's really fiberglass, you should be able to see fuzzy hairs of the actual glass fibers protruding from the surface if you use a pretty good hand lens.

1. 
   Kevin | Jul 25, 2003 06:12pm | #3

   clean and rough up the surface really well by washing then sanding or sandblasting.  The physical roughness may give you  most of your adhesion.

   That's true with any non-catalyzed, single component finish or paint. But, with any of the cross-linking catalyzed finishes it is definitely possible to actually interfere with adhesion by abrading the surface to a too rough texture. This is especially true with plastic substraits. As the finish chemically cross-links during the curing process, it will physically pull away from the deeper crevices on the surface, leaving less actual surface contact with the substrait.

   Another problem that has the exact same cause is what car painters call "sand scratch swelling." That is usually caused by less severe surface abrading that doesn't result in adhesion loss necessarily. In this case the slightly thicker wet paint film in the valleys caused by deeper sanding scratches causes the cross-linking finish to swell up and telegraph every contour of the sanding scratch valley into the surface of the cured finish. You don't really notice it with just a clear finish. But, it is easily noticable with solid color paints that are glossy at all.

   What I've found when painting plastics is that sanding with nothing courser than 400 grit is easily sufficient to promote adhesion without incurring any negative side effects. But, I'll qualify that by stating that this is with catalyzed automotive paints.

   Regards,

   Kevin