Talk Composites - The Forum for Advanced Composites

Skinning advice

http://www.talkcomposites.com/Topic20762.aspx

By MarkMK - 3/8/2016 10:55:56 PM

Not a technique I've had masses of experience with, but looking to do a little carbon skinning on some fairly small parts that have some subtle cosmetic features that I'd like to retain and not lose too much when adding material and coating

So, I was wondering if vacuum bagging the part once the fabric had been laid onto the tacky backing resin would help consolidate things a bit more tightly and help reduce the potential 'softening' of any subtle lines or features? I guess I'm asking if doing this will help to, in effect, de-bulk the single fabric layer and help make the skinned part a little closer to the original parts' dimensions and true form? 

Just wondered if anyone regularly skinning parts did this or if it's unlikely to make any noticeable difference? 
By mrlindeman - 4/6/2016 4:51:22 AM

My wife and I usually try to vacuum bag using an extra food saver. What we do is,  thin coat the part to be over laid with 2 part 5 minute epoxy glue. this takes about a half hour to full tack at 70 degrees F. Then we lay down the carbon fabric and cover all contours tucking and folding to fully envelope the part. If any extra needs to be taped to the back we will do that as well. Once the material is secured, we place it in a vacuum bag for a food saver or similar. You have to have at least 3 inches on all sides of the part of extra bag.

                Then situate the part while in the envelope/bag so that your cosmetic sides of the part have as little wrinkles of bag on them. Then start the vacuum process, working the bag by smoothing quickly to avoid as many wrinkles as possible. The bag for the most part will not grip the carbon and wrinkle the fabric itself. It usually will bridge but we are only doing this to hold the carbon to the contours until the glue/ tack layer fully cures.  

                Once the bag is sealed you can gently stretch and flatten the bag to smooth it out. Let this setup fully cure at least overnight.  Once cured take the part out of the bag, and then start the coating resin process using either the easy comp coating resin or in my case due to impatience and lack of money..... a good high quality art resin. Yes I said it, art resin. For me it works great and sands great, is thick and very very clear; but is not UV stable. Clear coat is a must, but should be used in most cases if the part is to be exposed to the elements in any shape or form. The art resin is a pouring resin for pub/bar tops and works at a 1:1 ratio due to its thickness  and self  leveling properties. 

                Your standard store bought art resin cures slow and needs very sanitary conditions just like the easy comp coating or art resin. Curing times at 70 F are about 72 hrs before you should sand and clear coat. I have had good success with using a heat gun on low after the resin has tacked out. The heat gun should be used a bit to help pop bubbles when first applied but not to much as too fish eye the resin. Just keep the gun at low and at least 20 inches away from the part in a sweeping motion when popping the bubbles. 

                Once the resin has come to a tack in about 4-5 hrs you can apply the second coat and repeat the bubble process until they stop popping. To accelerate cure time, let the second coat come to full tack and sweep the heat gun on low setting about twenty inches from the part for about 1 minute. Once the resin cools back down to room temp, it will start setting up. Curing overnight can be accomplished; but it takes sometimes longer. Its worth it though.