andrew-theasby
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| posted on 18/2/08 at 11:58 PM |
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fibre glass and polythene
Does anyone know if fibre glass resin will stick to polythene or not? I know it doesnt stick to parcel tape but id like to know for certain about the
polythene before i try it. (polythene sheet, not a carrier bag) Thanks
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colt_mivec
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| posted on 19/2/08 at 12:01 AM |
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Use a small test piece,Best way to be certain 
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dhutch
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| posted on 19/2/08 at 12:22 AM |
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I beleave most parcel tapes are polypropylene rather than polythene.
- However its very hard to get anything to stick to polythene anyway. Certainly epoxy resins dont readly stick to it. Not sure about polyester
resins.
Daniel
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Triton
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| posted on 19/2/08 at 12:29 AM |
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might react try a bit first.
If the stuff wants to stick it will even if you have waxed it...it's got it's own gremlins...
Mark
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Simon
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| posted on 19/2/08 at 01:10 AM |
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Andrew,
If this is a get around using release agent, I'd recommend trying ALL materials you will be using.
The reason I say this, is when I was amking my bodywork, I used brown tape as a release "agent" and it worked a treat for
fibreglass resin.
Great I thought, and lined the mould to my bonnet with it (yeah all of it).
Unfortunately, I didn't try it with gelcoat and I had a major reaction requiring a good few days filling and sanding.
So, best advice is to try it first I'm afraid.
ATB
Simon
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Benonymous
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| posted on 19/2/08 at 03:19 AM |
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Polyester
Polyester resin won't stick to polythene plasic. However. If you are going to use the polythene as a surface to mold onto, like putting a
90degree flange on a part. Make sure to stretch the polythene out and tack it down. The endothermic reaction in polyester resin will heat the
polythene and make it wrinkle. It may even do this if it's stretched or tacked, if your resin/catalyst mix is hot enough. A better tactic
would be to use mylar packing tape, or good old masking tape to lay up over. Neither type of resin will stick to these.
Epoxy does not have endothermic heat when curing so you could just go with polythene and stretch it and tack it a s I suggested.
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blakep82
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| posted on 19/2/08 at 08:16 AM |
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carrier bags are polythene, so i'd say it won't stick, but as before, mix some resin and pour it on, see what happens
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dhutch
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| posted on 19/2/08 at 08:42 AM |
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quote:
Originally posted by Benonymous
Polyester resin won't stick to polythene plasic. However. If you are going to use the polythene as a surface to mold onto, like putting a
90degree flange on a part. Make sure to stretch the polythene out and tack it down. The endothermic reaction in polyester resin will heat the
polythene and make it wrinkle.
I think you mean exothermic, but a very good point, polyethene is rediculasly temperature sensotive.
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twybrow
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| posted on 19/2/08 at 12:46 PM |
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Agreed - exothermic. And belive me epoxy does exotherm. I had a fire in my department last week because of it!
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NS Dev
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| posted on 19/2/08 at 01:36 PM |
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I have never had cling film stick to cured resin, but then I haven't done that much moulding!
I use cling film when fitting wheel arches (like manta 400 ones) to fill the arches out the the body and get a decent fit, when I don't want to
bond the kit on as I want to make it bolt on (proper job no bodge)
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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andrew-theasby
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| posted on 19/2/08 at 10:05 PM |
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Thanks for the tips, it was just an idea id had. Im not really using it to release anything, just when i added some glass cloth to the last job i
did, i had trouble with all the frayed edges trying to get them all to lay down nicely, just wondered about laying some polythene over it then then
smoothing it over by hand to spped it up, then peeling the polythene off when it had cured. Im still practicing/learning at the moment and going to
have a go with the chopped strand matt next which i presume will be even trickier to smooth out.
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adithorp
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| posted on 19/2/08 at 10:13 PM |
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I used a polythene bowl to mix up some resin today. I did a bit too much and the left over set in bowl. I just gave the bowl a twist and it came out
clean. So based on that I'd say no.
adrian
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twybrow
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| posted on 20/2/08 at 12:02 AM |
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Working with CSM is much easier. Use a dabbing (stippling) technique with a paintbrush. Dont be tempted to flood the surface with resin. Paint some on
the surface to be laid up, then add a layer of glass, and work the resin up through the glass. The edges should e fine. If anything they are easier as
they dont trap air.
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Triton
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| posted on 20/2/08 at 12:24 AM |
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Use a roller of some description to consolidate the matt and resin and remove any trapped air.
Mark
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Syd Bridge
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| posted on 20/2/08 at 06:08 PM |
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Poly resin won't stick to polythene sheet.
The boatbuilders around here use polythene all thge time for vac bagging.
Sheet is cheap and can be bought in rolls from Plastics by Post, here on the I.O.W.
Cheers,
Syd.
PS. Put the new layup in place,(mix with as little catalyst as possible,to give you working time), then put the polythene over the top and tape the
edges airtight. Then run a small tube from an old vacuum cleaner into the polythene bag, sealed around the tube. Turn on the old vacuum, and
you'll be amazed at how much the layup is compressed. It'll need sanding to smooth out though, when all is set up.
I've seen big boats done using as many as ten industrial vacs in one go!
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andrew-theasby
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| posted on 21/2/08 at 11:53 PM |
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Thats interestiing, so the polythene jusyt peels off then i would have thoought any wrinkles would have held it tight. Theonly time ive ever seen
vac bagging used the same meethod, but with mylar sheets in there
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