Minimum working temps for polyester resin

Poly v epoxy

The cost of using epoxy goes well beyond the initial cost of some resin. Once you apply epoxy all subsequent fillers, hi build and undercoats must now also be epoxy. Poly resin gelcoat finish much cheaper.
My only advice would be to use Iso not ortho.

 

Thanks to all, again.

 

I often use Polyester to repair Polyster hulls. Never had a real problem except with Coremat with EPS core and even that I got round with Polyester. Never had a structural failure either but then I tend to be fairly careful about the layup and preparation. On some older types with timber inserts I coat the timber first (bone dry) with a coat prior to putting any laminate cloth/roving on. Occasionally I will use epoxy as a complete seal (for the timber) then abrade and laminate Polyester but only in rare cases.

On the more modern Epoxy FRP builds use epoxy and any of a variety of suitable 'core' materials and they work fine.

Horses for courses. Use whatever is suitable, a lot of older hulls repair perfectly with Polyester and it is a lot faster to work than Epoxy as well as cheaper. At least the more modern resins have lost 'most' of the really powerful styrene smell....of yore.