So I screwed up and shot my flange with gel clear coat and when I put my vaccuum on it my tape pulled it up. Grrrr after fighting it over and hour I pulled it all off and made a big bag to go over the whole mold. I can get my part to 25 hg but can’t get my 27. I tried to figure out where my bag could leak but it’s all laid flat and sealed together with the gum tape. After 3 hours I gave up and had to leave. I’m so frusterated I can’t get a good vaccuum any suggestions. I can’t find a leak and it has to be tiny. I wish there was another way to seal vacuum bags!
double bag it
Is it possible to tape off your flange with packing tape before spraying your gel coat? Then there is no need to double bag, because the tacky tape will stick perfectly to your mold as intended.
Is there a diagram or a how to on double bagging ?
Yes I plan on that next time
When I double bag. Do I just pulled a vacuum on the inside bag?
Just use some no more gap filler ( or similar) to seal bag 
I use it everyday on painted flanges never have any problems with leaks The Tape sometimes causes more drama’s than it worth as the flange has to be very clean and with some tape they don’t stick well to semi perms.
Tim
Nice I’m gonna try that
From my understanding, he already bagged the part but sealant tape wasn’t sufficient because he stuck it to the gel coat. The bag is already on the part, therefor best decision in that case is to double bag it. Otherwise, you would need to remove the first bag, and re-bag, which would be a bigger waste of time.
Yes, you need to pull two vacuums, one inner bag, one outer bag. Separate vacuum circuits.
Yes I removed my first bag and then made a bag that the whole mold would fit in with sealer tape sealing the two bags. My frustration now is I can’t get rid of a pin hole leak somewhere.
Tell me why double bagging works? If neither bag is 100% will they help seal
Each other or are you still relying on a 100% seal on one?
I think if your mould is small enough then you can do a full envelope type bag (also a double bag) and leave the old bag in place
Or
You could remove the current bag and some of the cured gel coat from the flange only, so that you can then tape a new bag to the clean flange?
Opp’s. Didn’t mean to press the thank button :o
I find the most pin hole leaks come from the centre of the plastic not the seal. I hold the sheet up to bright light and most of the time you can see them.
Tim
air leaks will take the path of least resistance, so if there is a leak in the outer bag, the path it will choose is through the breather/flow media you placed around the first bag, out to the vacuum pump. However if both outer and inner bag has a leak that is in close proximity to each other, than there is risk to then go to the part. However risk greatly reduced. This is why when making expensive, or big parts/moulds, it is wise to use two bags, it increase your bag integrity, and lowers your risk of leaks, or even full failure. The cost difference is minimal, but the control is maximized.
I second the double bag. I do this when I have a part that is being a pain when I’m doing an infused part. It’s kind of a pain but not that big a deal if you get a perfectly sealed bag afterward. It’s definitely much preferred to starting the infusion and then later finding a leak and having to try to ‘fix’ it. If the part is small enough just make the second bag an envelope and it’s pretty quick and easy.
My part isn’t too bad it’s 55" by 38" roughly
Okay guys I got a vacuum to some what hold. I got it to 27hg after 30 minutes it dropped to 15 hg. Is this good enough to pull my epoxy? It gels in 40 minutes?
That will do the job
What are you building ?? Got any pics ?
Vacuum drop was 15hg in 30mins? If so this is way too high of a leak rate for a successful infusion. If measuring a leak by cheap analog dial gauge, I would do zero “noticeable” drop in 20 mins. However, better to use a digital absolute pressure gauge at the part, and do zero mbar drop in 5-10mins (depending on the size of part)if you want to measure the exact vacuum integrity of the bag and part.
It is a analog dial gauge at the catch pot. Guess I will go back to sealing something. Thanks for the help.