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Re: [PSUBS-MAILIST] Mini Nautilus Minisub
Well, I'm working with epoxy and glass right now,
and it's still too wet to go to the next step, so here's a few things I think I
know about this sort of thing, in case anybody is interested. Let's
see...where to start?
Some guys use either styrofoam or (even better)
extruded polystyrene foam (pink or blue insulation from the hardware store) as
the basis for a "plug" from which to make a fiberglass fairing shell from.
This is a good way to go, but there's a few things to know about it.
1. Bondo will "eat" (dissolve) these kinds of
foams. Bondo and some fiber glass resins contain chemicals like
styrene monomer which dissolves styrofoam and polystyrene foam. If you
make a shaping error and need to fill a ding in this kind of foam,
don't use Bondo. Instead, scuff it with coarse sandpaper and pour in
polyurethane foam. It will bond to the substrate without dissolving
it. A little goes a long way: "surfboard foam" starts as a liquid and
expands. Once you fill the ding, sand it as you would any other
foam.
2. Fiberglass resin will also eat styrofoam and
polystyrene foam (but not polyurethane foam). To protect styrene-based
foam from being dissolved, coat it with epoxy. Epoxy doesn't heat up like
resin does, so it won't melt the foam. It doesn't dissolve foam, either,
because it doesn't contain styrene monomer. But it is expensive, whether
you buy the amber stuff that comes in two tubes, or get it in gallon or larger
cans, the price is high in comparison to fiberglass resin. Worth it if the
project requires it, though.
3. Generally, curing time is a factor
in determining strength. Slow curing epoxy is a lot stronger than the
fast curing stuff. If you want to put a good strong protective seal coat
on styrofoam or polystyrene foam, use the slow-curing epoxy.
4. Once you have the foam sealed, you can
cover it in fiberglass. Scuff the epoxy with coarse sandpaper, and apply
the glass. Then, sand smooth, apply your finish, and you've pretty much
got a plug from which a female mold can be made.
5. If you just want a one-off fairing from
this process (and don't want to make a mold) coat the ourside of the foam plug
with several layers of fiberglass cloth for strength. Sand the exterior
and get it as smooth as you want it to be. Then, dissolve out the foam
core inside with a foam-eating solvent. What works for me is 100
octane low-lead av gasoline (airplane fuel, available at the local
airport). It will melt the foam away; doesn't leave a bad smell
when dry; cleans up easily with soap and water; and is relatively
inexpensive as solvents go.
6. Once the foam is gone, if you want to strengthen
the fairing, apply some fiberglass matting to the inside surfaces to thicken it
up a bit.
OK, I gotta get back to work. Any body want
to add to this thread on working with 'glass?
Pat