Duplicating Architectural Ornaments with Fiberglass Part 3

After creating the molds it's time to start casting the fiberglass. I tried Smooth-On's DuoMatrix Neo which is a polymer modified gypsum but it was too heavy for our application and I just wasn't sure it would hold up for exterior use, so I decided to go with fiberglass. 

 For my first test I tried using just  polyester resin and fiberglass mat, it worked OK but when I took the parts out of the mold there were a ton of pinholes in the surface that I would have to repair.  I have to make too many to spend all that time fixing the ones I have already made.

So I tried painting polyester primer (Ilva PI40) on the mold first and after that had dried a while
I applied the polyester resin and fiberglass mat and that worked perfect.

This is a video of the primer being painted into the mold,
the aerosol can in the beginning is Universal Mold Release from Smooth-On

Continued Part 4