Hi everyone, I was wondering if you guys could help me troubleshoot. I had some issues vacuum-bagging a 4' x 2' sandwich core panel. We used 18 oz. of epoxy resin/hardener for 27 oz of plain weave carbon fiber to follow a 40/60 ratio of resin to carbon fiber. We had a laminate sequence of 0/180/core/180/0. We had issues pulling a vacuum but we managed to achieve a vacuum level of 23 in Hg. During the layup, the carbon fiber seemed saturated with resin but I found today that the resin did not fully wet out the carbon fiber. We also had issues with striations on the surface and strands of breather sticking to the top of the layup. I believe our issues are a combination of not using enough resin (by not accounting for the resin uptake of the Nidacore) and not pulling a high enough vacuum. However, I would really appreciate any insight into this. I have attached some pictures of the panel for reference. Thanks!

I agree with Warren that less vacuum is usually best - I use 15inHg as a starting point but often 8 is plenty, especially with thin laminates... you just bleed off less resin.  The key is that you need to fully wet out the material before bagging - at least 50% resin by weight - and then use the bag - and release film and bleeder to pull off excess resin to get down to the 60/40 range.  For thicker laminates and with experience you'll be able to use less resin in the initial wet-out.  

Unless you're using it to press material into corners - which you shouldn't do - less vacuum will only reduce compaction and bleed, but should still be fine. With core bonding it can be good to use very low vacuum to keep from bleeding out all the putty.

Also, is there a way for resin or air to bleed out of the bottom skin?  If the Nidacore is non-permeable then air can't escape.  You'll get most of it with a careful wetout and good rolling with a bubble popper, but the core should allow air to escape, usually through small holes (in foam) but not sure about Nidacore...  

Alan, I am not sure I'd go along with the Airtech method you described - sounds like a good way to get lots of porosity.  Usually backing off vacuum is asking for trouble... but there may be something to it that I don't understand.