Hello,
In the past I have resurfaced a cast iron bath and some hand basins. I have done this using  2 or 3 coats of gelcoat..
It has been fairly successful apart from a few chips and yellowing over the years.
I am about to do this again on another cast iron bath ( which will be lightly sand blasted first ) and thought that this time I would first give it a coat or two of fiberglass resin then a coat or two of gelcoat, hoping that this would be an improvement.
Could you offer any guidance on this ? Thank you.

Just add 5% wax-in-styrene solution to turn the gelcoat into a flowcoat and solve that issue ^

Hello,
Thank you.
I was really hoping to not have the gelcoat turn yellow, even if it is only slightly. It has always dryed perfectly and quickly in the past.
 Are there two types of gelcoat ? If so what are the differencies?