Grumpy wrote:
Hi,

I am doing a gelcoat repair on an area that I have rebuilt. I was told tho,
to use flowcoat not gelcoat as the gelcoat will not harden. Any ideas please

Thanks
Alan




Sort of, most unwaxed resins won't fully cure if exposed to the air, so
gel coat (& most laminating resin) deliberately has no wax in it to take
advantage of this. The gelcoat is usually against the mould or at least
the mould's release agent on one side so no access to air & the inner
surface deliberately remains uncured (tacky to the touch) This is so the
subsequent layers of laminating glass etc will fully bond to the gelcoat.

You can use gelcoat to finish a repair on the outside & when properly
sanded, cut & polished you can get an almost perfect glossy finish,
something you can't do with flowcoat.

To make the gelcoat cure hard on the outside you need to stop the air
getting to it just till it cures, so you can add wax in styrene at a
rate of about 2%, but this will detract from the final finish gloss
achievable (still be much better than flowcoat though) or;

(i) Build the gelcoat up to a reasonable thickness higher than the
surrounding surface. You can easily apply multiple coats because it will
remain tacky on the outside giving good bonding to subsequent coats even
though it's been allowed to cure a bit.

(ii) Once you are happy with the buildup, apply the final coat & then
you can spray over it with normal mould release agent (cheap PVA is fine
& you can even gently brush it on once the gelcoat just starts to go
off; for you will be sanding minor imperfections etc anyway). The
covering of mould release will exclude air & the gelcoat will fully
cure, then you can block sand it etc.

(iii) Another just as effective way is to gently lay cling type kitchen
wrap over the still curing gelcoat, again it stops air & it fully cures.

(iv) Last thing, start sanding as soon as the gelcoat is cured enough
to allow it, the longer you let it cure the more difficult it will be to
achieve a nice blended flat finish. Never touch it without a sanding
block, don't be tempted to just hand hold the wet & dry unless it's a
tight inside corner or such. Lots of water & work it down with finer &
finer grades of wet & dry till you have it all at 1200 with absolutely
no gloss at all on the new gelcoat or the old surrounding (careful the
original can be very thin:-)) Then you can buff the shine up with
machine cutting compound (a slow electric buffer & green cutting
compound is fine) & finally a good polish.

All the stuff you need is at your fibreglass suppliers including good
advice, not at a boat place.

K