Clear coating carbon fiber parts with no gel coat.

General Composites Discussions Composites Talk
#1

So lately I’ve been trying to stay away from gel coats and I’ve noticed when I wet sand and wipe with a light solvent for clear coat, it looks good. But then when I clear coat it, I get tiny hairs. Like some hairs are absorbing the clear coat. I then have to wet sand and re clear which is a pain since my clear is $300 a gallon…

So what am I doing wrong? I infuse it with infusion resin from fiberglasssupplies.com. Should I reduce the resin to help saturate the fabric more? Or is this just how it is when using polyester / vinyl ester resins. I don’t want to use epoxies unless somebody can direct me an infusion epoxy that has a high heat distortion temp and a low cure temp.

The reason I’m trying to stay away form a clear gel coat on certain parts is because sometimes it cracks when demolding, and its a real PITA to apply and clean. That and time consuming. We’re a fast pace shop we don’t have time haha.

Thanks,

John

#2

hmm, i feel your pain. Try initially clear coating with a less expensive urethane clear coat. Let it cure, scuff it with 600 grit then reclear with two coats of the good stuff. Or mix up your cheap urethane clear ( $65 a gallon ) lay down two coats, let it flash, then hit it with the expensive clear. Let it cure 2 to 3 days then wet sand with 1000/1500 paper and buff if needed.

Reninfusion 8604/8604 epoxy is great for infusion. It is room temp cure… cures for demolding within 24 hours at room temp. It runs around $450 for 5 gallon kit… but imagine all the parts that will do at 6 gallons total. My only “beef” is how long it takes to cure for demold.

I have noticed with some vinyl ester resins they do not 100% saturate and bond to the carbon fibers. They do a very good job, but not as good as real epoxy. I would suggest talking to your resin manufacturer and tell them the problem… maybe there is something you can do to get the fibers completely saturated.

Composites One sells many types of VE resin… perhaps switching brands.

#3

In that case I think I should stay with double coating with the expensive clear since it dries to wet sand in only 15 min :(. But the epoxy might work real well! How about print through? All my parts go on cars so in California around the summer time I don’t want these parts to sit in the sun and then fall apart.

Last summer I made my mistake by buying a low distortion temp epoxy (110 degrees F) and after demolding it looked great, I put it in the sun for an hour and then it caved in… The surface temp at that time was 140 and this is Illinois.

Would this epoxy really saturate all the hairs? So when I scuff / wet sand the hairs don’t start sticking out? Also I guess I could always bump the heat distortion temp as well as the cure process by curing at 100 degrees F - 120?

#4

Saturation is an effect of surface tension. Get something with a low surface tension. A vinylester should do, but keep in mind that there are many vinylester species. (novolac, bisphenol A, pu modified).

As for an epoxy that survives California sun, carbon surface: forget it, unless you (post)cure at 80 degrees C or so.

#5

What about with a polyester gel coat?

#6

Again, only high temp stuff. I do recommend a Tg over 90 degrees C. (near to the point of boiling water) for both gelcoat and resin. (and a postcure, so your part indeed does reach that Tg. And moulds that survive the postcure…

#7

Ok thanks :smiley: