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Old 05 November 2005, 07:48   #21
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Quote:
Originally Posted by boatster_sr4
Gelcoat is just polyester resin. You can use a thick celophane to keep the resin from air while it cures, this is called Vacuum bagging.
Vacuum bagging, doesn't really describe laying cellophane over un-cured gel to stop it getting a sticky surface.
Vacuum Bagging is exactly as it says.
For the best possible strength & lightness, the main laminate in any composite structure should have the highest fibre to resin ratio possible, as the resin is only the medium that holds & bonds all the fibres, whatever they may be, in place and to each other, too much reduces the strength and flexibility.

Vacuum bagging is the process of covering the uncured laminate in celophane, with vacuum pipes attached at various points both in the celophane itself, and also at points around the mould. A vacuum is applied to these points decreasing the pressure tween mould & celophane to a level considerably less than that of the surrounding atmospheric pressure (approx 14.5), this causes all the excess resin within the lay up to be queezed out, and compresses the laminate to a very efficient, dense structure.

Most carbon fibre structures are made this way, but are also submitted to a greater pressure from the outside by pressurising the vessel that it's cured in, which is also an oven, as in most cases, C-F is cured with the aplication of heat to the resin pre impregnated fibre matt, so no catalist.

lots of 'suck', lots of 'squash', and a bit of 'warm', and you have a wing, or a tailplane, or a race boat.

Not trying to steal the thread, just wanted to point out that VB-ing is a little more involved that just draping a bit of selotape over some gel.

jf


PS. just realised this has already been covered, sorry to repeat.
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Old 05 November 2005, 12:27   #22
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Quote:
Originally Posted by slimtim
Can the cracks not be filled with that stuff in a tube (name escapes me) that uses capillary action to penatrate deep into hairline cracks and seal them tight?
Captain Tolleys Creeping Crack Cure! No it can't.

I've just "vacuum bagged" me cheese and pickle sandwich. Well, wrapped it in cling film.

A little knowledge is such a dangerous thing.
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Old 05 November 2005, 13:03   #23
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Ok forgive my loose verbage of the term "vacuum" bagging but it is still a legitimate method of laying thick celophane over the resin/gelcoat to help it cure and mold to the surface. This method is discussed in the West System boat repair manual just before the process of vacuum bagging. Its the same concept except applied for smaller repairs which is what Biggles' type of job requires.
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Old 05 November 2005, 13:47   #24
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Quote:
Originally Posted by Dirk Diggler
A little knowledge is such a dangerous thing.
Vacuum bagging, celophane, gelcoat, oh so dangerous! Watch out!
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Old 05 November 2005, 14:05   #25
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Quote:
Originally Posted by Dirk Diggler
I've just "vacuum bagged" me cheese and pickle sandwich.



Good one Dirk, I'm still laughing.
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Old 05 November 2005, 14:43   #26
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Quote:
Originally Posted by boatster_sr4
Gelcoat can come as straight pigmented resin, so gelcoat at times is in fact resin.
??? so what you are saying is you can use gelcoat instead of resin to laminate if they are one and the same???
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Old 05 November 2005, 15:48   #27
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Ah shucks, I might be wrong about the gelcoat as well. I do know that straight laminating resin is used with the fibreglass layup. You guys really know how to stick it to ya when someone gets it wrong. What a friendly bunch.

As far as any of the advice I gave in the original subject to Biggles it was purely from my own experience. I even stated it as such. Just trying to help a fellow out with a minor blemish on his boat. If you read my posts alot of the info is correct and helpful. Whats with all the snobbery?
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Old 05 November 2005, 16:02   #28
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Quote:
Originally Posted by boatster_sr4
Ah shucks, I might be wrong about the gelcoat as well. I do know that straight laminating resin is used with the fibreglass layup. You guys really know how to stick it to ya when someone gets it wrong. What a friendly bunch.

As far as any of the advice I gave in the original subject to Biggles it was purely from my own experience. I even stated it as such. Just trying to help a fellow out with a minor blemish on his boat. If you read my posts alot of the info is correct and helpful. Whats with all the snobbery?
oh stop bleeting! lol! i got the general idea with the celophane idea.... and the wax additive(4% styrene solution) is a far more widely used thing over here....

you say tamayto, i say tomartow.............hehe!
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Old 06 November 2005, 05:20   #29
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Thanks for all the replies folks.

I've been working over the weekend and haven't had chance to catch up on the forum.

I'm going to read this well over the next couple of days and then do the work maybe tuesday or wednesday. So long as the rain pi__es off.
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Old 06 November 2005, 05:30   #30
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If you need a large workshop for a fortnight you could do worse than have a chat with Rogue Wave, I am sure he do you a short term deal with light and power available to work on the boat in Drivers Wharf. I watched him do a couple of scratches on his Avon 4.7m, very impressed with the results he achieved.

Pete
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