Talk Composites - The Forum for Advanced Composites

Duratec Sunshield Voids Appearing

http://www.talkcomposites.com/Topic37854.aspx

By KLComposites - 9/10/2020 5:29:56 PM

This is happening intermittently, sometimes days after applying the first coat of duratec sunshield to parts. The duratec was sprayed on, then brushed in to fill some voids. After a few minutes flash time it was placed in an oven at about 140F to cure for a few hours. The following day, it was block sanded and coated again. The guy doing it didn't notice the porosity until I pointed it out, so I can't say for sure when it appeared exactly, but it looks to me like the first layer was still out-gassing while the next coat was applied. Putting it in the oven to cure the second coat probably exacerbated the problem. I suppose our recourse at this point would be to oven cure the first coat 24 hours or so before moving on, and we can be a bit speedier with the later coats. The duratec was not thinned or modified in any way. Any thoughts or experience with what's going on here?
By Fasta - 9/14/2020 2:54:35 AM

 
KLComposites - 9/11/2020 3:17:15 PM
Not disputing the presence of voids in the surface of the laminate - we're rescuing it with the duratec. The bubbles are forming in those voids between the first layer of duratec and the laminate, long after we've applied 2nd and 3rd coats of more duratec. 

Or are you saying there's air trapped in the laminate and we're causing it to escape by curing it further in our hot duratec curing process?

You can kind of see that the air is related to fabric as the those little air bubble lines are mostly oriented with the fabric. Air expands when heated .

Maybe just heating the parts well before applying the duratec could bring out the air first?? That is then filled with the first duratec coat.

Or it was just one part fault due to poor fibre wetting somehow?