Thanks again gentlemen.
I appreciate you both taking the time to answer the rookie questions.

I'll follow up with some images later as I get going.

If you go the plywood polyester router, you should be done after one session anyways.

You want to stick with one or the other.  Polyester can be applied to older layers after a week or so no problem, just give it a good key with sandpaper and a a clean.  Epoxy is the same in essence, once hard, a key and clean will allow the next layer to bond.

I would be concerned about budget and work environment.  If you are restricted on budget and stuck in a cool workshop then  polyester resin may be a better  choice due to cost and being less temperature sensitive.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Sorry @oekmont

Warren had posted that '
I've just googled and see seen what you're referring to now and understand.

Your point about the lack of attachment to the tinfoil, and hence core is a really good one. One I hadn't realized before.

Do you have any thoughts on epoxy vs polyester, given I may have to space out work on weekends? Would the polyester (unwaxed) allow me to come and add layers a week later, better than epoxy?

Regarding price: I know it will cost a lot. I've just graduated art school though and this is a big opportunity for me, as 1000s of people will see over the 6 months its out this summer. I am therefore committed to making it happen, and appreciate all the feedback you and Warren have given me doubly so because of it!  (ps. price and temp suggest polyester)

No, not like delamination. Fisheyeing ruins your surface, because the resin doesn't stay flat. Google it for pictures, than you will understand. Where did I mention delamination? I guess you meant my opinion to the tinfoil barrier? My concern here is, that the core isn't bonded to the tinfoil, and therefore the core isn't bonded to the laminate either. That way, the foam doesn't act like a sandwichcore, wich would be beneficial for your application (sandwich= good).
If you use epoxy, you don't need a forced ventilation, but a stable room temperature. If you are working with polyester,  you'll need good ventilation, but temperatures could be lower, to a certain degree.
Are you aware, that this would be a really expensive project? you should definitely try to build something smaller with the same techniques, to get a feeling for that kind of work. Especially when working with epoxy.

Thanks for the clarification Warren,

So like a delamination bubble? Oekmont mentioned that in the context of epoxies, but I thought polyester resins were supposed to be worse at delamination. Is that right, or are they just less adhesive?

Also, I'll be working alone and the project is large. I know epoxies need to (ideally) be worked before previous layers have cured. Is it true that polyester resins, if unwaxed, can bond well much later (say a week)?

Regarding heat, it seems like I may need to work in a heated area without excessive ventilation, and have a forced air feed coming from outside the building. Have you hear of that approach when doing composites in winter?

Most epoxies are quite temperature sensitive so we would recommend working in an environment above 15C and ideally around 20C.

Fisheying is when  a resin separates on a substrate due to the surface being "slippery " or not rough enough. This can be caused by the physical smoothness of the surface and/or chemical contaminants and release agents.   Imagine water beading and rolling off a freshly waxed car, same concept.  Coating resins are generally a little bit thicker which means they are less likely to split and fisheye when applied on a surface.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Poplar is quite the opposite of hardwood. And a rough pass with 1mm steps as final pass would be fine enough. No need for 3d contour here.

your right about the fumes during lamination. Although I am only using styrene free polyesters nowadays. Just that there are no wrong expectations here: it still smells, only less and (they say) less harmful, and it still attacks foam.

coating type epoxy is basically a usual epoxy, handles the same, behaves similar. But the formulation is optimised to inhibit the fisheyeing effect, epoxy tend to have. And they got good uv resistance compared to some other epoxys.
however, for complete outdoor use, you should get uv additive for the coating layers, or paint it. But if you are talking about automotive shine, I guess you also want the colour quality of a automotive paint anyways.

Hey @oekmont
My sincerest thanks for the brainstorming and thorough details.
Your awareness of pitfalls and suggestions are very helpful.

One issue with your second option (2) is that the CNC I have access to is more of a hobbyist model -- great for foam, but very slow for hardwoods.

That would have me lean towards your first (1) option: Some internal frame with XPS and Expoxy. Epoxy, although costing a fair bit more, would also be less offensive in terms of fumes right?
 - You mention a second layer of 'coating type' epoxy. I have used that type of product before, and am unfamiliar with the way it would differ form a composite epoxy. Will I need to worry about choosing my composite epoxy, in the same way as I would differentiate between 'waxed' and 'unwaxed' for early and final coats of polyester?  Also and importantly, it will be in the sun for 6 months. Does this sway your opinion about epoxy vs polyester, or would I just need a good jell coat / 2K paint over the epoxy to protect it from UV?

Based on your feedack, I'm leaning towards epoxy.