Epoxy is superior in every way (except price and the lack of gel coat) to polyester resin.  However, epoxy is not really compatible with polyester.  Why I say this is because epoxy can only achieve a mechanical bond and not a molecular bond.

I would suggest, if you are repairing a part laminated from polyester resin, stick with polyester resin.

You could, however, go with vinyl ester resin, which is stronger and more chemical resistant than polyester AND is will form both a mechanical and molecular bond with both polyester and epoxy resins.  https://www.fibreglast.com/category/Vinyl_Ester_Resins

Watch "1110 Vinyl Ester Resin" on YouTube


Keep in mind that vinyl ester resin only has a 90-day shelf life.  Make sure your project is on schedule and you will have enough time to complete it before your vinyl ester resin expires!

There is a valid argument that, once a polyester resin hull becomes degraded by sunlight and chemicals, there is very little molecular bond.  In this case, the superior mechanical bond of epoxy resin may be beneficial if that is all you have to rely on.

There are a number of epoxy resins available for marine use.  Based on my testing and experience, http://www.appliedpoleramic.com is by far the best.

As for what glass?

Watch "Fiberglass Overview" on YouTube


Watch "Stiched Fiberglass Overview" on YouTube


I would use a 6oz cloth https://www.fibreglast.com/product/6_oz_Fabric_38_inch_wide_259/Fiberglass_Fabric to cover the wood on all sides because resin by itself has no structure.

I would use a tape https://www.fibreglast.com/product/Woven_Fiberglass_Tape_217/Fiberglass_Fabric to laminate the cloth covered wood  into the hull, or you can simply cut your own tape from https://www.fibreglast.com/product/saertex-450-gm2-stitched-biaxial-fiberglass-2805/Stitched_Fiberglass.

Good luck,

Joe

(Attachment Link) Whats the best epoxy and fiberglass to purchase for building a new floor plus fixing hull(1973 Kona 19ft). I screwed the pooch because the original floor was so close to the hull and crooked so I sawed a thin line through a few inches of the hull(peekaboo garage concrete). I want it super strong because last season(2018) I spent $3000 bucks having the entire top and lower 140hp 2 stroke motor/tranny rebuilt. Thanks Brothers & Sisters. :banghead

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