Making Your Own Vacuum Bag
I have a job coming up that I would like to use the vacuum-bag process on, but the piece is far larger than my 9 foot bag – how has everyone solved this problem? Would it be possible to cobble together a one-shot vacuum bag with visquine and duct tape? Could the bag be taped to the substrate itself? Any help would be appreciated.
Then I laid up the substrate and veneer, and caulked on the top. I then had some 6mil polysheeting laid over the whole thing and duct-taped to the MDF table. I pulled a vacuum and there it was – it wasn’t perfect, but it held 12-13 inches and ran my pump constantly. For the one shot deal it worked great. With a little tweaking and a better membrane or seal, I don’t see why it wouldn’t work perfectly. My veneer was very flat to start with and only a 26x112" size.
From contributor K:
I have always made my own bags using vinyl that I buy from a wholesale auto upholstery supply store. It comes on 54" wide rolls, and can be cut to whatever length I need. They sell a contact type adhesive for gluing vinyl.
Whenever I need a one-off bag, I use cloth core carpet tape which is sticky on both sides. I keep rope caulk handy for stuffing a little pinch into any wrinkles, and around where the hose passes through the film.
On really large projects, I find it easier to do the glue-up right on top of the bottom half of the bag, then just peel the tape and stick the top and bottom halves together. I have not had any problem holding 25" Hg. on projects over 20' long. I usually use epoxy for my adhesive for this kind of work because of the longer open time and lubricity for bending.
From the original questioner:
I have come up with a few more questions. Contributor B: Is what you’re calling “6 mil polysheeting” the same as what’s marketed as “Visqueen?” The reason I’m asking is that people have told me certain thicknesses of Visqueen are waterproof, but actually would be air-porous in a vacuum bagging situation, which may explain why your pump ran continuously. Does anyone know of a membrane that is somewhere between thin poly and expensive vinyl? What tape works best for a one-off bag?
From contributor K:
To the original questioner: I have used other types of plastic films just taped together with carpet tape, as described above. If there are any gaps between parts or edges of pattern and high stack of parts where the bag has to really stretch across a span, you should expect an implosion if the PSI on the surface of the bag exceeds the strength of the chosen film, but you could use film as thin as a laundry bag from the cleaners if it totally conforms to the surface.
Some of the poly films that I have used had to be cleaned with acetone to get the tape to stick, then it seemed barely adequate, but by the end of the cycle, it could not be removed. Also, use cautions or dull any sharp corners.
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Comment from contributor T:
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