Looks like you still need to sand through a bad layer of resin - the rings of white show where you have gone through one layer to the next.

Multiple layers of resin applied at each B stage should not cause any problems on their own.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

So, I'm pretty much at my wits end.

It sanded down the part with some 80 grit and got the part pretty smooth . Whenever I wetted a part to clean it off the fabric would shine though nicely. Things were looking good.

On the advice on a friend, I left it out in the sun for a day to help any uncured resin fully cure. The next day, the party developed some blotchiness mainly at the surface but beneath as well. 


When the part is moistened, it looks like this:


I'm really getting fed up as I've put so many hours into this part and can't get any decent results.

Any thoughts on what went wrong?

Thanks guys
T

The white is the effect of the moisture from either sanding too early or a slight issue with the mixing ratio (and hence the blush you had).  In either case, the resin is left hydroscopic and hence wet sanding causes the white issues you have seen.

I would flat it back until the surface is smooth  and hopefully you will have cut through any  bad resin and be down to good stuff.  You can then coat over the top to give a final sealing coat.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

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