I used system three fairing compound cause I had it left over from anothe project. All resin will be poly because that is what I have used for everything and have a gallon left over. However you got me thinking now. Poly won't adhere to epoxy products well from what I've heard but epoxy will adhere to poly. Can anyone verify that or is it one of those old wives tales. It's just a hatch so I think I may still stick with the plan of using poly resin over the system three fairing and cross my fingers...

Whenever I've tried poly over epoxy I wound up with curing issues. It seems to react better if the epoxy has cured for a longer time like 30+ days and it has been ground to degloss it. If you want to push the envelope (and why not lol) I would try a test piece.
Rod

Ok change of plan, gonna buy a 3 quart unit of system 3 epoxy. Also gonna get two yards by 50" wide of 17 ounce double bias cloth to lay down over my fairing compound before the core then lay another layer on top. This gonna be strong enough? All will be purchased from Mertons in MA.

Personally, I think you have to go all epoxy now, or grind out the fairing compound.

I'd go polyester, personally, as it wets the mat. And I'd just clean it up with a 36 grit belt sander. I'd skip the hull and deck putty, and pre-wet the nidacore skin. The nidacore I have took resin well. I used it with VE and 1708 for my "Whaler bench seat/tank cozy" project.

You do want thickness under the nidacore/ for the topside of the hatch for penetration resistance. Much less is needed on the underside.

With respect to mat- plain old biax may lay flatter, so you might want to skip that on the topside of your laminate (the bottom of the hatch). It gave me fits. ( I made note of this)

I would also put tape or biax in the trough section of the layup- for better screw and screwhead holding.

I in-lined rather than linked a pic of the finished product (with PVA and bits of glass still on top. I put peel ply on top, then paper towels, edit: THEN 4 MIL POLYETHYLENE SHEET, then plywood, then car batteries. That was almost too much and started to dry out the laminate, but that's because it didn't kick for nearly a day. That approach should be fine for a normal layup.

And no, the H80 core isn't centered, but it works.

Yes. And if I were to go epoxy, that's about what I'd do.

That epoxy layup will certainly work strength wise but it'll pricier than a polyester lay up for sure. I agree with Fishstretcher and would use polyester for this job.
Rod

I've never used epoxy before so this will be a good piece to tactics on despite it being about twice as much, at least I'll learn something. Thank you very much!!

I will throw this out there because I always do.

Mertons sells a nice vinylester epoxy. It has equivalent or better mechanical properties to a "conventional"epoxy. It seems even better than some. But the cure system is like polyester. MEKP and cobalt. And it wets out mat and you can thin it with styrene monomer. It is also said to stick to "conventional" epoxies and polyester. It certainly has for me. And some sailboat guys use it for just that. The formulation he sells is very thin- good for infusion. It is also quite reactive- it will gel in sunlight withou MEKP.

People think it is like polyester because of the styrene smell but vinylester is the short name. Generally it is listed as an epoxy- vinylester epoxy.

So that's an option

I have posted extensively on this before- with a bunch of data. If you are interested I can dig it up.

Be careful with conventional epoxy- you can develop an allergy to the hardener and never be able to use it again. So use the gloves. A few layers so you don't muck up the wrists when you peel off gloves.

General rule of thumb re: epoxy and other resins:

Epoxy over everything, nothing over epoxy.

;)

Perfect:D