vacuum bag keeps leaking

General Composites Discussions Composites Talk
#1

can’t seem to find the leak anywhere, but lately i’ve been getting leaky projects that go to the scrap pile. i got these bags locally and yes, they were built for vacuum bagging.

what i do is i setup an envelope-style bag where i cut a 2 foot bag for a 1 foot part and i fold it in half, seal two of the sides, slip my part in, seal the last side, and insert the tube. usually when i finish the vacuum (which holds well while the pump is on), then i’ll seal the vacuum line using a air-tight valve i installed, and before it held the vacuum well. but lately, air starts to leak in very slowly, messing up my project. what am i doing wrong here? im about ready to give up vacuum bagging at this point and just stick with wet lay-ups.

#2

There could be many different things. You’ll never know for sure until you get yourself a leak detector. Sometimes it’s in the way you put the sealant tape down, sometimes you have a sharp edge somewhere in your mold that’s puncturing the bag. If you had no leak before and it’s starting to develop now on the same mold, try cleaning you mold really well. Cured resin buildup from previous layups could have sharp edges, corners to them that will puncture you bag easily. Vacuum bagging isn’t difficult, but if you don’t know how to diagnose the problem then it’s frustrating. There could be many different reasons why you’re getting leaks too. I’ve only suggested a couple of possibilities.

#3

the molds were fresh, but it might be possible that a sharp edge might’ve caused the problem. i’ll have to look out for those problems on my next project thanks.

#4

us more breather fabric if you think that your mold is puncturing the bag!