Idea to eliminate bubbles under top sheet

[pmg]

Hi,

tried to answer in viewtopic.php?p=35928, but it always throws me back to the index page.

So, I will try to press a cap with topsheet soon. So there is no way the bubbles can escape to the side once pressure is applied. Made up my mind a lot about dealing with this, but until last night no good ideas came to my mind.

But then, as always when I try to sleep, shortly before drifting off to dreams, a simple idea struck me:

If you lay up the normal way (layer by layer in the mold), you will always have the trouble that you will trap bubbles between the topsheet and the layer underneath (lets call it second layer for now)

So, why not alter this process a bit?
1) Put the top sheet flipped somewhere else, and put the second layer on top and roller these 2 together. Like this, all the bubbles should escape through the second layer.
2) flip this package again and add it to your layup. Like this, the bubbles will be between the second and third layer (e.g. the wood core).
3) Use rollers to get most of the bubbles caught between second and third layer to the sides.

In my case, the second layer is a thin fabric with a quite wild design.
What du you think about this? anyone tried already?

Cheers

[twizzstyle]

Clever idea, but whether the bubbles are between layers 1 and 2, or between layers 2 and 3, if your layers are translucent or clear after curing (i.e. fiberglass) you'll still see the bubbles.

I've done a couple of pairs with clear top sheets and have had zero problems with bubbles. Just don't throw the top sheet on there, unroll it gently so no air gets trapped, and if some does, use a roller or dry squeegee on the topsheet to push the bubbles out. Easy, just don't rush it.

If you're vacuum bagging your top, as long as the epoxy has sufficiently low viscosity (heat will help) and long enough curing time (heat will hurt), it should draw most of the bubbles out. You don't get the aid of the vacuum with just a firehose. You are literally boiling the bubbles out of the epoxy.

[pmg]

Sounds good - my epoxy has a very low viscosity and 300 mins cure time :)

Well, if the second layer is not transparent, it should work well. Will give it a try.

[twizzstyle]

Sounds like this deserves some testing. Don't test it on your skis, use some scraps and try a few different methods and see what works best, then use that method on the skis themselves.

[MontuckyMadman]

If any of my previous posts on this could be somehow retrieved and read then maybe someone would know the answer.
Its trapped air in small crevaces. It cant escape cause its trapped.
Surface must be smooth. Try a pre treatment.

[pmg]

Yes, there is some trapped air, and I doubt there is a way of completely getting rid of it. Thats why I want to try to have the little rest of trapped air between the second and third layer, unvisible.

[MontuckyMadman]

Pmg. You are wrong. Try a pretreatment it can be eliminated.

[twizzstyle]

He's not entirely wrong. Outgas your epoxy with a vacuum chamber prior to layup, be very careful and unroll the topsheet on, and then vacuum bag the the topsheet, you have a pretty decent chance of getting any tiny bubbles out even with a rough-ish surface. It's not much different than doing vacuumed layups of composite parts in female molds. When I do that I get tiny pinholes in the fabric, but no "bubbles"

[pmg]

I always degas the resin before using it. And am always impressed how much gas is pulled out!

@MM: What kind of pre-treatment are you talking about?

[MontuckyMadman]

It took me a year to figure it out.
Try stuff, fill the holes.

[pmg]

First try today, 100% success. Not a single bubble below the topsheet. Its this ski: http://www.skibuilders.com/phpBB2/viewt ... 6951#46951

[gozaimaas]

Nice work pmg.

[pmg]

Hi,

just took another pair out of the press. Its the first one with a sublimated topsheet. I put a layer of normal white cloth between the topsheet and the carbon fibres to get a white background (used whitened exoxy).

Now I can answer 100% that this method works, there is not a single air entrapment, only the structure of the cloth is visible through the topsheet. Came out perfect. Will post some pictures tomorrow.