If Gelcoat is used in a female mold then no filler / fairing should be
required.
If paint is used over glass then usually some amount of filler and fairing
would be required.
The weight of filler under the pain should easily exceed the total weight of
gelcoat.

Having said that I wouldn't think that the weight difference between gelcoat
and painting would be significant enough to worry about and it would be
pretty difficult to accurately calculate. If painting so much would depend
on technique.

wrote in message
ups.com...
I think we're talking ablout two different construction methods...
"Gelcoat" generally implies female mold, fiberglass laminate
construction with polyester resins, where the colored gelcoat is
applied against a release agent, (preventing the gelcoat from sticking
to the mold) followed by a few to many-many layers of fiberglass of
various weaves & thickness. Here, the 'color' is the *first* item to
be applied (against the female mold).

"Paint" is generally used in male mold construction, mostly used in
"one-off" boat building. (Paint is also used over "old gelcoat" after
it has faded after years of sun/abuse/neglect). In M-M construction,
various materials (cold-molded wood, sheet "foam", fiberglass planking)
are laid over a male mold with the hull thickness then laminated up
(often using epoxy resins) with either additional wood veniers, woven
or knitted fiberglass, kevlar, carbon fiber or what-have-you.
Here, the paint (color) is applied *last*, against a primer that acts
as an adhesion base for the paint as well as a barrier against any
epoxy 'blush'.

As to the weight: One applies Polyurethane paint in multiple (like 3)
*very* thin coats. I'd guess you could do a canoe with about a quart
of paint / solvent / reducer which might weigh (guessing) about 2 lbs
(total).

MW
Los Angeles