On fiberglass, gel, due to how slick will be difficult. Other than washing I didnt do any real prep. On the new flashing wiped with paint thinner. I also wanted the extra sealing, if just blacking out might be a better product.
If rolling on a product first coats will look pretty bad. When I redid ours didnt think about slickness of the added aluminum flashing. 1st coat roller kinda slide around, I was thinking this isnt going to work.
I had the same experience when I rolled the bed liner on our truck. Even though I had sanded it 1st coat just was bad. However 2nd coat is where it starts to build/cover. So I continued on camper.
On the al first coat I 'helped' the roller just to get product on. Let it dry, subsequent coats back rolled in one direction once tacking. Let it set for an hour, roll on another coat and it started building. Think 3 coats, Next day I rolled 2 more coats. All coats, dont dry roll, but dont over work too wet (or youll be back to square one for coverage). If it matters, rolling with any high solids product it will be textured, last pass (each coat) needs to be rolled in one direction. Bottom line its the film build up when rolling.
I coated aluminum flashing, galvanized tin angle, poly tank cover, primed wood, and previous coating. Only real problem was the exposed section of rear bumper, powder coated white. Its even more slick once wet & just sliding around. Just mopped and let dry. Took several coats before film thickness started to cover.
