[Biplane-Hangar] Fiberglass mold release question.

[biplane-hangar at lists.aviating.com]

PVA is polyvinyl alcohol. West Marine carries it as "Evercoat". It's used  as 
a mold release agent and also a a curing agent for polyester gel coat. I'm  
not an expert on this stuff, but as I understand it from my childhood  
boat-building days, polyester resin comes in a "coating" variety, and a  "laminating" 
variety. The coating resin develops a sort of wax coating that  causes it to 
cure hard, whereas the laminating resin maintains a bit of  tackiness to 
promote adding of more laminations. Evidently spraying on PVA will  cause the 
laminating type of polyester resing to cure hard. PVA is pretty neat  stuff...it 
looks like purple water, sprays on clear, and dries to form a  plastic-like film. 
It washes off easily with water. This is the first time I've  used it.
 
The curing property isn't a factor for Epoxy resin; I don't think there's a  
specific "coating" epoxy. But the PVA seems like a good mold release  agent.
 
The aluminum tank is painted white, and the fiberglass is quite clear, so  if 
the tank is leaking, fuel can be seen between the shell and the tank. One can 
 "palpate" the shell and see the fuel move around. That's why the shell isn't 
 bonded to the tank. If it's leaking badly enough, fuel will drip out of the  
overboard drain.
 
Doug




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