2 questions on skinning techniques

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#1

Ill make an introductory post once i finish up two more completed parts, but i have had 2 major problems so far.

1- getting my carbon to stick to my part nicely.

I have been skinning plastic parts so far. after i degrease, sand, and prep with alcohol i have been doing a thin coat of epoxy resin and waiting for it to tack up to stick the carbon to. I will wait to where its just far enough into the curing that the resin won’t soak through my fabric much at all. But even an hour after that it wont get tacky enough the the fabric will want to stick firmly, which creates lumps. Am i not letting it tack off enough? should i switch to a spray adhesive?

2- My first wet out will get applied and i have been using a heat gun to pull the bubbles out which works great, but if i try to let that tack up and add another coat of epoxy resin, again using a heat gun, it will pull bubbles from the first coat and get stuck at the top of my second coat and leaving pinholes. I need another technique here i think.

Should i look into vinylester?

#2
  1. Not quite sure what you mean, so let me get this right, you put down thin layer of epoxy and let it go tacky.Then laminate over the top of it. Is the problem you sometimes allow this to fully cure instead of going tacky - so its a timing thing for you? If so, when fully cured, you will need to sand and degrease again due to the formation of amine blush, an oily like substance that doesnt bond well to anything else. If its tacky, you’ll be grand and wont need to do this.

2)Vinyl-ester is certainly worth looking at, also polyester which has a considerably lower chance of forming air bubbles as well. Im guessing its not structural anyway so are there any benefits to using epoxy? Have you a nice clear resin? Im not sure about bonding ability of polyester with plastics as skimming is something I havent done, its probably not as good as epoxy I would guess (depending on grade) but may save some money also

#3

  1. no, the opposite. i think i’m not waiting long enough for it to get tacky to lay down the fabric. I cant seem to get my fabric to stick to the epoxy, it keeps pulling away.

  2. These most recent bits are lip spoilers for the bottom for a car bumper and i wanted it to be durable so i went with epoxy. Yes i have epoxy resin from US composites. 635 thin resin i believe.

#4

I noticed you’re using a heat gun to get bubbles out of the resin… is it possible that you’re using too much heat and the resin is actually curing too quickly? Also are you sure the bubbles are coming from your first coat into the 2nd? I’d prefer to get the first coat bubble free, then go onto the 2nd coat if you need.

What is the cure time on your resin? If you say that you’ve waiting so long that it doesn’t soak into the fabric at all, then maybe it’s too long? Even if you put the fabric straight onto wet resin, there shouldn’t be any lumps after you brush or squeegee it out. But even if you don’t have much resin coming through the bottom of the fabric, the fabric should stick down just fine when you start to brush more resin on the top and wet it out fully.

#5

I’ll take a shot at your problem…
It sounds to me like you aren’t letting it sit long enough to tack up. Epoxy can take anywhere from less than 15 min to as long as 8 hrs in my experience it just depends on what brand and hardener you choose. This is why I believe a lot of people doing overlays or skinning choose to go with polyester resin as the times are reduced greatly.

#6

To me it sounds like you’re appling the build up epoxy too soon. Coat the part, and when it is tacky enough for the carbon to stick apply the carbon. Watch corners and edges for lift but let it sit overnight. At this point the carbon should be adhered to the part. Now build up the epoxy and finish. If you apply the build up too soon it will just soften the adhesive layer of epoxy and release the carbon.