FRP is not a tight surface *at all* (even if you don't see any pores).
Soaking a FRP part in acetone is certainly not a good idea.
However, wiping such a surface with acetone to remove grease or whatever
doesn't put a problem because the thin film of aceton left behind will
rapidly evaporate from the surface.
On gelcoat, however, I wouldn't use acetone, but rather ethyl alcohol.

"Martin Gregorie" wrote in message
...
Bruce Greef wrote:

I would be very careful about using Acetone on a glider, depending on the
construction you could do damage. Reliable sources indicate that acetone
can penetrate the structure and damage the foam core in GRP/foam sandwich
structures.

I'd agree. Speaking as a model builder who molds his own composite
structures for wing D-boxes and fuselages, I'd like to make the following
points:

- the glass/carbon skin *should* be impervious to liquids but you
never know. The problem with making light, strong composites is
to get excess resin out of the layup after you've wetted out the
glass or carbon. If the wetting is thorough then blotting out as
much resin as possible and then curing under vacuum will leave
you with a compacted structure with no pinholes etc. However, if
the wetting wasn't right you will get starved looking patches that
may well be porous.

- Model dope thinner is mostly acetone. This dissolves white polystyrene
foam almost instantly. A standard way of making complex one-off glass
fuselage shells, fuel tanks etc. is to carve the shape from white
foam, cover it with glass cloth and epoxy and, when the epoxy is
cured, pour thinners onto the foam. Result: an empty shell all ready
for finishing.

- acetone wets composite surfaces really well and will wick through the
finest pores or cracks.

The moral is to test any unknown liquid of a scrap of foam (if you can get
one) before putting it on your glider unless you're certain that the area
you're working on is absolutely impervious to liquids *and* you're sure
the liquid can't run onto any part of the structure that might be porous,
cracked or has poorly adhering glue lines.

HTH


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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