How much vac pressure can you apply when bagging without getting 'pin holing' in the surface of the laminate?. Answer in Hg (inches of mercury' please for those of you with imperial gauges. Does it vary depending on the weight of cloth used?

Thanks Mike. I was using thick breather but I dont know what type it was I think it was dacron. As far as pressure goes, I understand that one atmosphere is equal to 30 Hg (inches of mercury) so your pulling about 10 Hg if your operating at 1/3 ATM. Apparently blue foam is Ok up to about 18 Hg but I dont know for which density (I do some tests) As far as resin goes, I'm told Epoxy resin is safe to use on blue foam when using carbon or Kevlar.

Jamie.

Hi Guys,
2 things, I look forward to being corrected however in my experience the likelihood of generating a pinhole free bagged laminate is as good as zero. I know a few amateur and ex-professional makers in WA and we all wet layup our final coat with a low weight, very tight weave glass, no bag.
b) experience with avon descent powerboats (yes they are high tech constructions) suggests that while you may save 50g in weight by pulling the last bugger alls of resin out via bagging you will suffer a significant loss in impact resistance, resin sucks up damage very nicely.
You can generate a pinhole free laminate but generally not via bagging it has to be either labour intensive wetout or via the generation of non vacuum derived external hydrostatic pressure (you can pick your own method but they are all a hassle)

L

so what pressure is that in PSI. because those naish pumps can go upto 7 psi and cutoff (or what ever pressure you set it at). so anyway this could be an easy vac, with no construction needed as well as a practical use outside of construction.

why walk when u can sail?

where abouts can i buy some Divinycell 5/8 inch foam ive been looking everywhere

I suggest to anyone who is unsure of the pressure unit conversions, visit joshmadison.com/ and download CONVERT.

If CSM fixes pin holes I want some!!!
So what the f is it????
What do those letters stand for?

ps hesion sounds like a bad idea, I'm sure it has a "wick" action this will suck the resin out of the layup. A non wick action soaker layer. won't suck. The excess resin is just squeezed out by vacuum pressure, the soaker layer just gives it somewhere to go.

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Originally posted by sinker

CSM is chopped strand mat

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Oh that stuff!

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what type of peel ply are you using?

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Don't know actually, just bought it from the shop, it's a greyish very fine material coated with release agent.

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How long do you leave the bag on for?

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overnight usually or until resin is well set.

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What resin do you use.. gel time?

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varies, at the moment I'm using botecoat, sets in about 6 hours.

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There shouldn't be that much resin getting through the peel ply into the breather layer,

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There's heaps mate, depending on how thick the lay up is, the worst is when carbon is involved, I'm never sure when there's enough resin with that unlike glass, when it's obvious when it's wet out.

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I get the feeling that far too much bag-pressure is being applied.

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I use about 1/2 atmosphere

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We are talking about resin infusion here aren't we?

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No idea, what's that???

I think most people making boards at home lay up all the glass, wet it out, lay peel ply and breather cloth then stick it in the bag till it has all gone off. (Thats how Ive allways done it anyway) Resin infusion would be pretty tricky for most backyarders.

Well why bag then?

If you're wetting out and laying up/rolling by hand you should be able to calculate the exact ammount of resin to use (glass/resin ratio) so shouldn't have to reduce the resin content.

I imagine if you leave a bag on for 6 hours there will be a bit of pinholing because the glass/resin ratio would be too lean.

Or is there another theory at work here?

Guys,

I am interested in making my first foam core kite board. But I have my suspicions about the benefits of the vacuum bagging. Specifically I see the logic in what sinker is saying.

I have read previously that the glass has a certain strength with a certain ratio of resin and that more resign simply adds more weight.

But I can not immagine that there would be that much weight saving by vaccuum bagging such a small kite board, as opposed to a large boat which would use a sh@t load of resin, so I am wondering the following.

1)Has anyone any estimates of how much resign to use for say a 140cm TT kite board, I would imagine it to be a 1kg to 1.5 kilos max.

2)Has anyone actually measured the before and after weights of the blank glass and resign to determine how much is being pressed into the breather cloth, by the vaccuum. i.e. is it a half kilo or less??. I would imagine that you would be using at least a kilo of resin on the board.

3)As the strength of glass is along the cloth, does anyone think that if the rails were overlapped in a traditional hand layup like a polyester board, that it would be stronger and require less glass matting, my theory here being the main strenght is in the rails, not the flats.

4) what is with the long gel times for epoxy, can you not get 1hr gel time, why is the gel time so long for such a small job. I suspect the gel times are so long because guyes like Sinker need a heap of time to difuse the resign into the job?

5) I have a fridge compressor, Im looking for the parts to make a circuit, especially check valves, a solonoid preasure release valve and pressure controller. I dont particularly want to spend all weekend mucking around with an old vacuum advance from a car. can anyone advise me if I can use normal pressure phnumatic fittings or are there special vacuum equipment suppliers. Anywhere good to get these near Caringbah Sydney?

I am not opposed to the vacuum bagging as I see it will save time sanding.

Thanks

Please advise Andrew

Just a guess but I dont think bagging a board that small will make too much difference,especially if you've never done it before. If you're worried about too much sanding then use a layer of peel ply over your glass job. It's easy to do and gives a much smoother finish.
Have fun.

eightfootplus , there are a few epoxys out there so shop around the the price changes alot . i use FGI R 180 with fast hardener now that it winter the gel time is about 2 hour which is very fast . any faster than that and it will heat up to much and melt your foam core if you use styreine . as for vacum baging if it is for kite boards i always use a bag beacuse it is the only way to hould the klegie cell in place ( to get rocker and concave perfect every time) you are best to make a rocker jig. but if you are making one of back yarder it will take longer to make all the tools you need than to make the board . but no matter how good you hope it will turn out you will have to make at least half a dozen boards before you get the idea how evey thing works .
the vacum bag is the greatest invention for boardmaking since since foam . and should be used always . it reduces the glass , epoxy ratio . compress the lay up , prestreches the cloth and form moulds the klegie cell and the list goes on ,
after saying all that for one board you can get away with (only kite boards) make a jig and weigh the board down with sand bags .not to heavie may be 2kg each,
i have made quite a few kite boards and my best advice is to put concave in it has it will help alot with the stiffness and use a smaller than you think amount of carbon .
good luck and go for it