Is CoreCell Air Tight.. Leaking Vacuum bag

[FirstLight]

Just finished a layup of some carbon over corecell for a rudder and having a heck of a time getting more than 15 inches of vacuum. It's either the corecell or the bag. The sealant tape is directly between the bag and the corecell.. The adhesion between the tape and the foam is very good.

It's either the corecell or the bag.

Ran out of the good stuff and am using the 3 or 4 mil plastic construction stuff bought at the hardware store.. Bag is about a year old so perhaps it has degraded in a way that will allow air to permeate?? Although it has been in a closet and not exposedto UV..

Any ideas??

Thanks,

R

[KnottyBuoyz]

I've never been able to hold a vacuum on any stack with that kind of plastic. Finally bit the bullet and got real vacuum film and no more problems. Dunno about the core-cell though. It's supposed to be closed cell so you'd think it'd be airtight but unless it's perfectly smooth you'd have a hard time getting a good seal. We're building a rudder too (articulated) and was actually thinking of doing a full bag and hang it from the rafters so it's totally enclosed then infuse it from the bottom up. Going to do a half scale trial first!

[FirstLight]

I think it is the bag that's causing problems.. I've seen photos of folks using a bag over corecell before.. Perhaps they hot coated the foam with goop before vacuuming over it..

You are a brave man with the infusion.. I have a hard enought time getting a seal as it is.. If I'm not perfect on the bag I don't cry too hard since it's only a bit of extra resin here or there.. But with infusion, I hate to think of seeing $300 - $400 in material go down the drain on a rudder.. Although I suppose repair are possible..

I've got some flat sheets of Nida-Fusion I'm looking to infuse for 'furniture' and floorboards and non-critical bulkheads. I figure I'd try it on 2 x 4 piece and if that worked would scaleup to the 4' x 8' sheets. I'vegot a super flat 5 x 10 tablewith a formica sheet on top so I think I'vegot a shot..

We'll see..

[KnottyBuoyz]

Do a search on User "Ausiwik" aka Steve Marshall, he's downunder in Australia and is putting together a nice little trawler in foam core and infused. Looking for his site link right now. Here it is....

http://marshalldesign.blogspot.com/

He's doing some large size infusions and appears to be having some great success with them. I have other links somewhere at work I can look up tomorrow.

I tried the cheap route on the consumables with no luck and a lot of wasted epoxy & fiberglass. Eventually you'll realize there's no substitute for the proven materials. I had my share of failures but am getting the hang of it. Bought some carbon fiber biaxial fabric to enclose our rudder with. Still toying with the idea of making my own carbon fiber rudder shaft. Don't really know why but I'm trying to eliminate as much metal (especially underwater) from the boat as possible.

I was getting a lot of leaks where the pleats joined the butyl tape. A dab of acoustical sealant fixed that. I've seen guys use two rows of butyl tape too.

[AndrewK]

I am infusing with epoxy and the cheap 150 micron plastic from a hardware with no problems. Have not tried sealing directly to the foam, I resin down a 1 - 1.5 inch strip of peel ply first and seal to this.
I have also found that it is better to put a small piece of tacky tape under the pleat.

[marshmat]

CoreCell is closed-cell, yes, but it's not perfectly impermeable against full atmospheric pressure.

The extra few dollars spent on proper bag film is worth it. 6 mil poly, the stuff sold as a vapour retarder at Home Depot, can barely serve its intended purpose, let alone hold a vacuum. Airtech sells a wide range of pretty good ones from $1.20 a square metre, http://www.airtechonline.com/econo/econo_a.html .

Sealing those damned corners.... bad memories of late nights at the shop.... in the end, it ends up being enormous globs of bag tape everywhere, and plastic flash tape over the edges. Sealing for prepreg and sealing for infusion are both a fair bit harder than sealing for hand layup; even small leaks can make it fail.

[Polarity]

Hi
Doubt the corecell is 100% vac tight, and also seriously doubt that you will get a good enough seal to it with the tacky tape due to the open cut cells on the surface

We infuse almost the whole of our Class 40's - Hull, deck, bulkheads. Build gallery here: http://express40.com/coppermine/index.php and we have some top notch guys doing it - one thing I have noticed that our best guys put a bag on, vac test and infuse, the less experienced spend 20 mins in the middle looking for those damn leaks!

Cheers !

Paul