> Hans Jrgen Danielsen wrote:
>
> The manual states that a second bake must be done after
> filling - before priming, and my question is: Is this really
> necessary??
You mean the current Europa manual? Surprise there, as baking raises
the glass transition temp of the epoxy, for best strength of the
fiberglass structure under hot conditions. The filler though is not
structural, and the epoxy therein will bake on its own in service,
raising the transition temp, if exposed to hot enough sun.
> My next problem is UV protection. Do I have to apply silver before
> paint, or can I just spray on a layer of clear Polyurethane UV
> protection as final top coat?
Silver is a physical UV barrier, which is best. PolyFiber used to
sell a dark gray UV primer, touting its being a physical barrier, but
now sells a white primer they claim is equivalent, but presumably now
a chemical barrier. As does a competitor, but they say that all
chemical UV stabilizers are sacrificial. Namely they eventually break
down, but paint does eventually anyway, but protect the underlying
substrate in the interim. That's what's in the UV poly clear coat you
reference. It's to protect at least the paint, to prevent fading of
color coats. Unknown if it's effective to protect the structure
underneath. That's why at least I, and a few others here, prefer to
stick with products that are specifically intended to prevent UV
degradation of fiberglass aircraft structure, cause even if we knew
the chemistry, we don't know what's in a product intended primarily
for painting metal.
Regards,
Fred F., A063
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