Carbon fiber layups - who does a second coat of epoxy?

[lt130th]

After the first round of epoxy dries and your cloth is hardened, who follows up with a second coat to "fill the fibers?" If it matters, I'm using West System 105/207 on 3k 2x2 twill. I don't really see any spots in my layup that a second coating of epoxy would "fill."

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[kfxguy]

It will make it stiffer, but more brittle. Did you go over it with a foam roller? That's all that's needed.

[lt130th]

I put on a thin initial coat, layed the cloth, rolled it to press the resin and then applied the top coat with foam brush, and rolled it afterwards with a fine, foam roller to even it out/suck up the excess. I don't see that it needs a second coat, but I'm falling back on fiberglass processes. This is my first turn with carbon. From what I have seen, with respect to epoxy and carbon fiber cloth, less is more for strength.

[kfxguy]

You got it.

[jcald2000]

Yep!

[larryrose11]

If you use a vacuum bag or compression process, the peel ply that compresses the fibers in place makes the CF mat looking, and in this case I use a faom holler with a top coat to give it a good gloss.
If you just doing hand layup, what your doing is good.

[olwarbirds]

Travis, brother you do nice work...Im sending you my next hull to CF

[kfxguy]

Travis, brother you do nice work...Im sending you my next hull to CF

Thanks!

[tlandauer]

Travis, brother you do nice work...Im sending you my next hull to CF

ditto! lol...

[ray schrauwen]

Do you mean that if an extra layer of epoxy is applied to hand laid c/f cloth it's weaker than not?

This is my first turn with carbon. From what I have seen, with respect to epoxy and carbon fiber cloth, less is more for strength.

[Chilli]

I think you did a nice job. If you look closely at small white reflected areas of the CF cloth in the second pic, it looks like the fibers were well saturated and the epoxy wasn't too thin. On some of the Fighercat CF layups I've seen, the epoxy was thinned out so much, it looks like the carbon fibers were not event bonded making the hull flexible. Any additional epoxy is just going to add weight. Maybe make the hull a little stiffer but not necessarily stronger.

[lt130th]

Do you mean that if an extra layer of epoxy is applied to hand laid c/f cloth it's weaker than not?

The way I understood it when researching was, when doing hand lay-ups with carbon fiber cloth, you don't want to use a lot of epoxy. For example, using a roller to apply thin coats of epoxy between layers of carbon fiber cloth is better than pouring on the epoxy and spreading (like how you might do a fiberglass cloth lay-up). Intuitively this sounds non-sensical, but I haven't researched beyond this hear-say to understand why less epoxy would be "stronger". If you've ever studied material science, you know the term "stronger" could mean many different things so who knows.

[ray schrauwen]

Thank you!

[iridebikes247]

less epoxy is definitely not stronger. This might make sense though if comparing two hulls and one has a higher epoxy to cloth ratio with multiple layers of cloth meaning one hull was vacuumed harder or something, making the cloth-to-cloth bond less "tight."

When doing inlays I have used multiple methods, including the spray adhesive technique. I still use it once in awhile but I think the best way to get a good bond is to brush epoxy inside the hull, wait until it tacks up and press in your pre-cut cloth that fits. You'll only get 1 maybe 2 shots at positioning it otherwise you'll distort the weave because of the tacked up epoxy pulling on it. At this point brush on the epoxy, when done wipe the hull down with a lint free rag or roller to absorb all excess.

-Have used this method in 3 of my mhz hulls where extra strength was desired. A chemical bond (hull fresh out of the mold) will always be better than letting a hull cure, then sanding it and creating a mechanical bond with the epoxy but it is possible to get fantastic results using the above steps.

[lt130th]

...making the cloth-to-cloth bond less "tight."

Maybe that's it. The context from which I took this information was during a process of applying multiple layers of carbon fiber cloth in a hand-laid application. Perhaps the point is simply to not have excess epoxy creating "gaps" between each layer of cloth...? When doing fiberglass layers you can pour the epoxy out in a pool on top of your dry cloth and just spread it with a flat trowel. Afterwards you often apply a second coat of epoxy to fill in. So my confusion came from these two peices of information that seemed to conflict.