Question about carbon fiber finishing

Hi guys, first attempt at vacuum bagging an enclosure. IMG_20180927_170140

Question: The surface of the enclosure is opaque in some areas and lucid in others as if while removing the peel ply tape (didn’t checked it) some epoxy remained on the tape. IMG_20180927_170149 IMG_20180927_170155 IMG_20180927_170201

Why so? Is it normal or is it bad? Bad curing of the 2 component epoxy?

If it’s hard, then it’s epoxied, it’s good but it just has a smooth surface finish of epoxy. If it’s soft, epoxy didn’t get into it. Sand the shit outta the whole enclosure starting at a low grit and work your way to a high grit. You can apply layers of epoxy or a clear coat once you do a bit of sanding, and then keep sanding an applying, it’ll make the carbon pop and look amazing. There is a thread here where people added carbon layers to decks, they have the sanding/clear coat steps down to a science.

Thank you @MrHappy, is it this?

Yeah! Check that thread out for how to make that enclosure shine. Sanding is gonna take you hours and even days, but it’s worth it.

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It is Lucid in some areas because those areas didnt get vaccumed down making contact with the peel ply. Most peel plys leave some texture to the finish as they are porous allowing extra resin to seep through to get soaked up by the breather bleeder.

What are the materials you are using? There might be a better way for you to get a better looking finished product. Some CF I have used is much better than others… also what kind of vaccum?

What are you using for a mold? I have figured out that if you don’t have a great setup the best way to get to quality looks is to go the route of skinning an enclosure… they come out much better for me at least with my hobo set up…

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Well typically you get a glossy finish on the surface between the mold and the part. So in your case, that should be the inside of your enclosure.

I usually 3D print my enclosure negative molds, sand it, bondo it (if I want a very smooth mold surface), apply a gel coat, then 7 layers of release wax, and 4 or 5 layers of PVA. Then will start laying my cloth. This will lead to a shiny surface. But it is quite time consuming and the gel coat, wax, PVA, mold plastic, and bondo make this quite an expensive part if you only make one.


The mold is very shiny and the finished product will reflect this finish. The vacuum ply will leave the part dull.

Here’s a simple fiberglass part from another mold



Hi @Sender. That’s exactly what I suspected. So I wet sanded the porous surface just a bit and then applied a final layer of this two component epoxy resin, which I also used to sandwich the 2 layers Glass fiber + 2 layers Carbon fiber before. I used a 0,9 bar / 0,95 atm vacuum pump and some Toray 200 g/m² 3k 2/2 twill CF. Final result is good, I will post later some photos of the same uneven spots. I think wet sanding was a good idea because it helped me understand when to stop sanding: basically when you pour some liquid on the sanded CF fiber you have sort of a preview of the epoxied surface. The wooden mold was a nightmare: too many sharp edges (a real pita to lay the cf), used not enough mould release agent so I had to destroy the mould in order to free the enclosure: IMG_20180927_114905

(yes @baxtred, lesson learned: next time at least 7 layers of release wax).

I thought about skinning the enclosure as well, but I read on here that vacuum-bagging would grant extra mechanical strenght, and then I thought what would happen if a stone/sidewalk hit the enclosure hard. Thanks for the advices anyway

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I’d highly recommend using PVA along with your wax. It creates a film between the mold and your part. You can brush a few layers on (letting it dry between) then begin laying. Here’s a fiberglass enclosure straight from the mold. It’s not painted but rather uses a gelcoat that I applied to the mold prior to laying the fiber.


Don’t get resin in your pump! I personally don’t vacuum bag my parts and they turn out fine.

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