Greetings from Toronto, Canada!

I recently submitted an idea to a sculpture festival, and they've accepted my proposal. 
Now I have 3 months to build and install it (totally self funded as well).
The following is a quick overview of my experience and tools.
If any of you offer advice I'd be most grateful.

Current Experience and Tool Access:
- have a high rez 3D scan file of a Toy Giraffe
- have been doing small layer CNC carving on an X-Carve from 3D tool paths generated in Fusion 360
- have basic knowledge of silicone mold making and small casts (from previous projects)
- have very basic understanding of basic layup process, and some of the differences between epoxy and polyester

Tentative Approach:
- cutting many (84) layers on the CNC mill out of foam, basic finishing
- EITHER building up layers of fiberglass on top of the foam (with tinfoil layer if polyester) or making a number of larger molds and doing layup into the molds.
- the fear is with adding material on top of the mill work, I will lose most of the detail if it is to be strong enough. Making molds on the other hand adds many more steps and material investment (silicone, mother molds etc)

Seeking Advice on:
- how many layers of what kind of fiberglass and resin I will need to make it strong enough that it will be OK if people climb on it?
- any suggestions on epoxy vs polyester? Polyester is appealing for my budget, and also because it will be ouside for 4 months (I've read the epoxy doesn't like the sun).
- any other general approaches.

p.s. I have access to a space where I can leave work to cure for weeks on end (regarding polyester fumes) but it isn't consistently heated and Canada is pretty cold in winter.


MUCH MUCH thanks for any direction or suggestions on my approach, what I might be missing, or what I should be researching.

It doesn't take that much reinforcement for a foam structure to take the load of people climbing on it. But if people are permitted to climb on a sculpture, they usually end up doing much worse.
 I would start of by using a styrene resistant foam. This is much more expensive, but also much more resistant against delamination. If you use something like airex, the sculpture will already be strong enough to gently hold a person on top. And it's still much cheaper than taking moulds.
Than cover it with 450-600 glass mat and polyester resin. Done right, this will not affect the details. Sanding and painting. This will give you a really strong sculpture. Only thing to worry about would be the joints, as I don't know what exactly you got in mind there.

By far the easiest way would be to carve it in foam and coat over in fibreglass.  Use a layer of epoxy on the surface so the polystyrene doesn't get eaten into.  You can then use polyester resin and woven fibreglass to coat it to add strength.  The detail looks fairly generic so you could modify the 3d model to make it stand out a little more so that when covered in fibreglass, the slight loss in detail is made up for the fact you made the detail more proud.  Depending on how fine you need to be, adding a mm or two of fibreglass to make it very strong should still leave the detail intact.  You can sand any edges or fine detail to restore edge "crispness".




Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hi Gentlemen,
Thank you both very much for your replies and insight.

Oekmont, I was originally planning on XPS foam as is readily available (with a tinfoil barrier), but I will look into Airex. That sounds interesting!

Warren, do you think the thin layer of epoxy (good trick) would be better than tinfoil? Would either matter in terms of the bond once it's embedded in polyester and woven fiberglass?

Would you also give me a sense of how many layers / coats I would need to reach 'a mm or two', and the best weight / weave for that? Would that be the 450-600 Oekmont suggested?  I don't have much of a sense the relationship between strength and composite thickness.

Finally, as you say, it would be far easier to build and coat, then build, mold, a layup in mold etc. However, this will also mean I will need to put in more muscle to the finishing right? Would putting a coat or two of resin over the final glass layer give me enough to smooth down to a perfect finish? I'd really love to have the work give a polished, automotive type level of finish, and am willing to put in the work. Wondering if that will be possible in terms of building up a coat or two of resin then sanding back.

Much much thanks.

Tinfoil will do you no good here, because the styrene will get through the gaps and attack the foam. And it separates the foam from the fibre reinforcement. This way, you won't get a sandwich structure, but a loosely foam filled fibre structure, wich will be far less stable, as the shear forces can't be transmitted through the foam.
A epoxy coating has a different problem: lamininating polyester doesn't bond to epoxy, no matter what you do.
An automotive finish will be a real challenge for a rookie.
in my opinion you got 2 choices (excluding mould making, wich will be a whole different story) wich will lead to a structural and visual high quality product.
1: the epoxy/xps  route. Take the densest xps foam you can find. And reinforce the neck and legs with a rod on the inside. Xps get's wobbly pretty fast. Than reinforce it with several layers of woven glass of 200-300 g/m^2. Something like 4-6 layers should do the job. You can sand it with coarse grits and add additional layers, if it's still not strong enough. Finally, sand it smooth, and apply a coating type epoxy. and a second coat at the b stage. After curing, sand everything smooth with finer grits. From there on, you could spray paint it with automotive laquer.
2: the polyester route. Ok, I can't find any affordable pvc  foam anymore. But  you are cnc'ing anyways, so you might as well create a hollow poplar plywood structure out of interlocking semi circles (to save material). This should already be quite strong. The reinforcement only has to strengthen the structure across the individual layers. A single layer of 450-600 g/m^2  chopped glass mat will do that with quite some safety marging. After curing, sand everything smooth. Than apply polyester top coat in your desired colour. Carefully sand everything smooth, and wet sand to high grits. Finally, polish to high gloss. You could also paint it after flattening the top coat.

The second route would also make it very easy to  make the sculpture in several pieces, with hidden joints, wich will make everything way easier.

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.

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.

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

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?