By Telram - 8/14/2018 8:45:50 AM
Hi guys,
I'm in the process of working on my first composite project which involves skinning an ABS plastic car spoiler. I'm about midway through the project and wanted to get some advice for the subsequent steps as I've come across something strange.
Forthe project I used some 200g plain weave CF fabric and some 3:1 high strength epoxy resin that is supposedly meant for CF/kevlar fabrics.
After abraiding the surface with 80 grit sand paper and keying the edges, I put a coat of well mixed and accurately measured epoxy. Once at the b stage about, 1h45min later, I laid the CF fabric and teimmed the excess. Another 3 hours later a second heavier coat of epoxy was applied. All work occurred in a clear environment which was at a constant 20-21C. The results looked promising at this stage:
Once cured, about 5 days later, I re sanded with 180grit and 80grit to take down the low spots and used a dremel to take off the hardened overhang. I now applied another 5 coats, of epoxy, where each coat was applied to the previous at the b stage, about 1h40min.
It is at this stage I noticed the epoxy starting to turn milky near the surface, in more of a streaky fashion. This was most visible by the 4th coat and 5th coat. I left the spoiler to cure for about 30 hours. The epoxy did harden and looked like this:
Suspecting the streaking was some form of amine blush, albeit the surface was hard and I could not wipe off the streaks, I proceeded to wash the part with warm soapy water and a rough sponge. Once I dried the surface the epoxy had turned white with the same streaking patterns becoming more pronounced. Luckily I only washed a portion of the spoiler, however the more I tried washing off the supposed amine blush the white the piece became. It is worth mentioning that the epoxy in question is a non blushing type.
After initial washing:
After additional washing:
Worth mentioning, when the part is wet the epoxy shows clear and the weave is nicely visible. It is only when dried that the part returns to the whitish color.
At this stage, I'm at a bit of a loss as to what I've come across. I still need to block sand the part to remove uneaveness in the part. I was planning to add a final coat of epoxy and then do a final polishing but was hoping to get some advice from the community first. Any thoughts or comments on how to proceed are welcome.
Thanks for your time guys!
Telram
Montreal, Canada
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By Dravis - 9/9/2018 12:28:32 PM
I have been "skinning" and doing hand layup and Infusion for maybe 10 years now, and my conclusion is solid: Skinning and getting really good results is NOT worth the effort if you have a part you can make a mould from and infuse the part .. out comes a REAL carbon fibre product, lighter and stronger than the "original" - the work needed to make the plug, the mould and doing an infusion is much more satisfying than skinning.
Succesfull skinning is like doing a really top end paint job, painstaking attention to cleaning and degreasing, sanding and polishing. "soft and flexible parts are a bi*** to do, and you NEED a dry and warm room to work and cure the parts in. AND the room needs to be clean and free of dust .. Timing the B-stage of covers is essential, get it just slightly wrong and you loose adherence or mess up the surface of the first layer.
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