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how mutch vac to use ?

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not annonymous
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Re: how mutch vac to use ?

Postby not annonymous » Mon Jun 24, 2013 11:59 pm

mattthieu wrote:i'm using only polythene film over the laminate, no release no breather.


If you are not using a peel ply and breather, then how do you expect the bubbles to come out of the laminate?

Where do you expect the excess resin to go?

With excess resin in the laminate, how do you expect the pressure exerted by the vacuum to effectively compact the laminate?

When I was doing a lot of vacuum bagging with a clear resin finish, I found it was pretty easy to get dry spots in the laminate with too much vacuum. These dry spots would become obvious as a fairly uniform whitish haze after the laminate was fill coated with clear resin.

To eliminate the problem, I limited the vacuum to 15-18 in hg measured at the vacuum inlet to the bag. The amount of vacuum you need with your set-up need might vary however, depending on what you are using for your breather and peel ply, or if you are using a perforated film to reduce resin loss.

Trent

FrederikS
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Re: how mutch vac to use ?

Postby FrederikS » Tue Jun 25, 2013 10:48 am

The process is wrong, you need to allow for transportation of the air bubbles on top of the laminate once they have been expanded. That is what the breather, bleed, perforated film is for.

This is a German company's handbook for laminates. Even though the site is in German the book has English translation included.

http://wiki.r-g.de/index.php?title=Date ... ndbuch.pdf

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Re: how mutch vac to use ?

Postby mattthieu » Tue Jun 25, 2013 2:12 pm

i was using one of the yellow sqeedgees from resin ( clean one ) to sort of sqeedgee the air bubbles to the sides wheres they would disapear ( as i vac from the bottom and have a sort of big piece of cloth on the bottom side of the board to help air to travel into ths hose ).

i got most of bubbles out but, not all.

will try it with release film and breather next time i do a top of board ( hell, it might even give me and antislip finish on the top off my board without adding any salt afterwards !!).

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Re: how mutch vac to use ?

Postby zfennell » Tue Jun 25, 2013 8:40 pm

mattthieu wrote:i was using one of the yellow sqeedgees from resin ( clean one ) to sort of sqeedgee the air bubbles to the sides wheres they would disapear ( as i vac from the bottom and have a sort of big piece of cloth on the bottom side of the board to help air to travel into ths hose ).

i got most of bubbles out but, not all.

will try it with release film and breather next time i do a top of board ( hell, it might even give me and antislip finish on the top off my board without adding any salt afterwards !!).



your way can work.
and can give good results if done carefully.

but you need to move excess resin and air about 10" with your squeegee.
with peel ply and breather, the bag only needs to move the excess about .010".

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Re: how mutch vac to use ?

Postby foam-n-fibre » Thu Jun 27, 2013 11:58 am

What did you say you are using on top of the board? Is it plastic like the vapour barrier plastic that you buy on a roll at Home Depot? That stuff is not stretchy enough and probably will want to wrinkle. Go get yourself some vinyl, like that stuff that some people use overtop of a table cloth. You should be able to find it on a roll with paper in the roll too, at a fabric store, or even Canadian Tire. If they have 2 types, get the thinner stuff, it holds wrinkles less. With this stretchier material it should be easy to move bubbles, and they should come out to the edge fairly easily.

I have not done this over wood though, so if there is a source for air within the wood then that could be a problem. It seems to me that in a very low pressure environment a small bubble can expand to be bigger (assuming it can't escape or be absorbed into something). In that case, you probably don't want to use a huge vacuum if you don't have a good way for air to get out. Do your layup carefully and cleanly. In a thin glass skin over wood, the amount of resin you will suck out may not make a noticeable weight difference anyway.

Peter

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Re: how mutch vac to use ?

Postby mattthieu » Thu Jun 27, 2013 2:29 pm

i actually dont get that mutch bubbles, but, does not look clean ! yep, it's cheap vapor barrier

i just god some strechlon, from a freeman counter, and fairly nice epoxy ( got one that is transparent as water and coats really well, will give you updates ).

so, i'm assuming strechlon is going to to the job !

will try table cover stuff for the next project !


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