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May 21, 2019, 11:11 AM
plane destroyer and builder
skybattle's Avatar
Thread OP

Air bubbles?

Hi to all carbon fiber fans,

I am making some pieces with spread tow carbon for the first time... and the pinholes appeared. I did some tests first, so I thought that applying the resin with a roller would eliminate the pinholes. NO.

The process I followed is:

- Resin in the mold (semipermanent mold release; laminating resin, not UV resin)
- 25 gr fiberglass (applied with a a small paint roller before setting it in the mold, in both sides)
- Heat the wet fiberglass to eliminate bubbles
- 80gr spread tow carbon
- 1mm balsa
- vacuum and pressing well the laminate in order to eliminate bubbles

The result in the pictures.

I am painting now with clear coat 2k paint trying to cover the holes. Let's see.

What is your opinion? Are they air bubbles? How do you do it?

P.S.: The spread tow carbon has right and reverse! What an interesting discovery! Of course I put it in the wrong way!
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May 21, 2019, 05:56 PM
Balsa breaks better
Thermaler's Avatar
Looks a bit of the dry side, maybe a little more resin.
Is the balsa sealed? Could be sucking up some of the resin leaving the fabric dry.

Others with more knowledge than I will help, they helped me.

To those folks, Thank You!!


Who knows more than he did but not all he needs to know. ;>)
May 21, 2019, 07:45 PM
Suspended Account
That's why you use pant in the mold, it covers the pinholes.
If you you want that posh carbon shine you might need to use some thickening agent to the epoxy on that first 25g fiberglass surface coat, just like gel-coat. After that when laying up the fiberglass/carbon layers you use your favorite rapid floating epoxy.
May 21, 2019, 11:11 PM
Registered User
Since you are vacuum bagging you must degas the resin before molding. It would be wise to spray the mold before starting the molding process with your clear coat 2K paint. Just a thin/light relatively dry coat will do.
May 22, 2019, 03:43 AM
Registered User
Ward Hagaman's Avatar
I’ve had issues with woven carbon and too much resin sucked into the breather. I now wait a while...say, 1/2 an hour before I add the core to the outer skin. I also only use perforated plastic rather than peel ply so as to not suck too much resin out.
May 22, 2019, 11:02 AM
Barney Fife, Vigilante
tom43004's Avatar
I would not use glass over spread tow... but that's a preference. When using spread tow alone (textreme or A Spread) I usually roll epoxy on the mold surface and sprinkle a very light bit of cabosil on the epoxy to keep it from migrating. Also, as Fnev states, clear coating the molds will have the same effect, though may not be as durable.

Non-woven materials like carboweave or carboline don't need the cabosil as much as woven materials but definitely do benefit from a clear coat.
May 22, 2019, 02:00 PM
Registered User
Ward Hagaman's Avatar
A highly respected composite modeler, Adam from WyomingWingWorks? suggested that the best way to avoid pin holes is to wet out IN the mold...that way the layup is “happy” and saturated.
May 23, 2019, 04:35 PM
plane destroyer and builder
skybattle's Avatar
Thread OP
Thank you for your suggestions.

I use perforated film and I also perforate the balsa, but I didn't seal the core this time.

However, my previous test was without balsa, and the result was similar (perhaps a little better as you can see in the picture).

Is it a good idea to laminate de carbon fiber and let it cure (without vacuum), and put the core the next day as a second step? Does it solve anything?

Thanks again!
May 23, 2019, 06:10 PM
Registered User
Ward Hagaman's Avatar
That's sort of what I do by waiting for an hour or so before adding the core and the vacuum.

I still think that you should try wetting the mold first, lightly heating the resin to pop bubbles, and then wetting the veil cloth IN the mold. Then use Phil Barnes' method of using enough resin so that a gloved finger raises up a puddle when pressed on the carbon. Then wait for a little while before adding the core and the vacuum.

This last step is my idea...and could break some composite rules but the rest is pretty well proven by the experts.
May 23, 2019, 11:09 PM
Registered User
Originally Posted by skybattle

Is it a good idea to laminate de carbon fiber and let it cure (without vacuum), and put the core the next day as a second step? Does it solve anything?

Thanks again!
Nope, sticking to cured resin is nowhere near as strong and curing it all in one go. The previous suggestion of mixed a small resin batch, wetting out the carbon and letting it tack out a little is the best for adhesion. Clear coat on the mold/mylars is the usual way I've seen for best finish.
May 24, 2019, 05:29 AM
Registered User
Roguedog's Avatar
You said laminiting resin was used. is it an infusion resin?

Cause it looks like to me it just didn't wet out completely. Usually a problem when the resin has a high viscosity. Should be 500 cPs or less for vacuum bagging.

Also most epoxy resion will cross link for the first 12 hours. But yea a continuous lay up is best.

Just doesnt look like bubbles IMO and if that's the case even degassing wouldn't help.
May 24, 2019, 11:59 AM
plane destroyer and builder
skybattle's Avatar
Thread OP
I'm using this resin. It's an infusion resin:

I'm going to do two tests, one with clear coat on the mold and the other one without it. Both letting curing the resin for 1-2 hours before adding the core. I will seal the core and I will not perfore it. Of course with perforated film (I don't like the peel ply because easily demold your piece when removing it).

I will put pictures of the results.

Thank you very much for your suggestions. Playing with spread tow carbon is not cheap! But the result is impressive!
May 24, 2019, 01:19 PM
Registered User
Roguedog's Avatar
Yes it says it's for infusion but that depends on the hardener used. nothing mentioned on which hardener.

According to the data sheet the resin has a cPs of 1000 and then depending on the harder used like the 1053S hardener then lowers to 253 cPc (mPs) but with the 1059S hardener is 637cPs.

The 1053S is the one needed for infusion.
May 24, 2019, 01:51 PM
plane destroyer and builder
skybattle's Avatar
Thread OP
I use the 1055S hardener for 1h30' gel time.
May 24, 2019, 02:11 PM
Registered User
Roguedog's Avatar
That may be the problem. It's hardening before it completely wets outs the carbon fiber.

The viscosity of the 1055s is 362 cPs so that would be ok if it had a longer set time.

Like i said before it doesn't look like air bubbles. Looks like it didn't have enough time to flow out properly, and if you heat it up your accelerating the cure time exponentially,

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