Hey guys , I gelcoated with two layers my pattern about week ago…
and I couldnt finish it with fiberglass. Now I have gelcoat layer for over one week. If ill put fiberglass on it will it bond? should I firstly sand paper gelcoat for better “contact” or maybe put fresh third coat of gelcoat and then proceed with laminating?
laminate over the existing gelcoat and it will be fine
Yeh if you work for Boeing then it’s start again time, but on a home-made, non-mass production mould, you can just laminate over the existing gelcoat and it will be fine. Your mould possibly won’t last 10 years if that matters 
I normally just give it a quick wipe with acetone to clean off any contamination that has occurred, and if you’ve laid it on nice and thick then a quick scuff up with 60 grit won’t hurt. I find acetone is normally enough.
I’d check to make sure none of the gel has released from the part. The outer surface is fine to glass to but I had a similar situation and as I started the layup I noticed that in a couple areas the gel had released so had to start over.
thankss guys, i laid on existing layer. same question goes to rapid laminating poly resin , may i make a 1 day break between layers?
Not to be Nancy Negative here but I’ve repaired boats that have had secondary bond issues because the gelcoat or laminate was left to cure past it’s open time. That being said, sometimes an acetone wipe can do the trick, sometimes it’s sanding. There is also a product called Bio-Lock 9000 that works extremely well for surface prep.
Yes you wouldn’t do it on final parts. But on a mould, you’ll be fine. As I said, a mass production mould would need to be made to a standard, but a home made mould will be fine.