Topsheet with a vac table? Can it be done?

[dbabicwa]

Hi gents

I am after some advice about a topsheet.

This is my third attempt to build a kite board with a topsheet and vac.

Not happy with a results. Whatever I do, I get some dry looking spots under the topsheet (well, bottom sheet actually).

The FG is 200g/m^2, wetted with about ~130g of slow epoxy. Topsheet wetted with 30g and placed carefully on a FG from the middle. Used rubber roller to squeeze bigger air pockets out.
Than I just vac bag it in a vinyl bag with no breather or anything. Again using a roller to work out the air out on a sides.

Pls see below:



So, a question:

Is is possible to achieve really good looking results with a vac and topsheet?

Or is it my technique which I need to change? How do you do it?

Cheers
D.

[MontuckyMadman]

Dont you want a breather?

[dbabicwa]

Tried that, the same.

Used a lighter FG cloth as well, the same.

[MontuckyMadman]

Its trapped air. Looks like its in lines? Lack of compression in those areas or wood is trapping air or epoxy is over worked and foamy with air.

[dbabicwa]

Thanks mm,

The lines are reflection from behind.

This "dry" smaller spots are of my concern.

[twizzstyle]

Do you have a pressure gauge on your pump? Sure you're getting a good strong vacuum?

Should always be using a breather when vacuum bagging, unless you're doing resin infusion. I don't think lack of breather is causing your issue, but it's still something you might do differently.

[MontuckyMadman]

Try presealing the wood to fill the small poors.
Is there a composite layer there?

[knightsofnii]

wet out both sides? ie the glass and the topsheet
are you using a medium viscosity epoxy?

I have bubble issues similar when i do clear, but they're so small it hasnt been an issue as of yet. And I'm using a press.
It seems to be for me that it happens in areas where part thicknesses change, its happened more around the perimeter of my boards than inside

[gav wa]

Would using a press help?
My press is finished, I'm just finishing off other items like my heat blanket control box etc. You are in the same city as me and are welcome to use my press if you want to try that.
We would need to make a mold though.

[gozaimaas]

Air will still get trapped using a press if you dont bring the pressure on progressively to swueeze out the trapped air. Kind of difficult to do

[gav wa]

Air will still get trapped using a press if you dont bring the pressure on progressively to swueeze out the trapped air. Kind of difficult to do

I have been toying with this idea myself. I have 3 X 4" hoses in my press, so been thinking about pressurizing the middle one first then 2 minutes later open the outer two.
Anyone else tried this.?

[dbabicwa]

Do you have a pressure gauge on your pump? Sure you're getting a good strong vacuum?

Should always be using a breather when vacuum bagging, unless you're doing resin infusion. I don't think lack of breather is causing your issue, but it's still something you might do differently.

Thanks

I do have a gauge. Tried with a breather as well. Problem with a breather is it will imprint with any irregularities, hence a thicker plastic sheet like 0.5-1mm must be in between.

Try presealing the wood to fill the small poors.
Is there a composite layer there?

Good idea, thx. I do think I've sealed 2 of 3 boards tho. Same results. If the air is trapped, it's trapped. No way to get it out.

Layer on top is just glassed Paulownia wood.

wet out both sides? ie the glass and the topsheet
are you using a medium viscosity epoxy?

I have bubble issues similar when i do clear, but they're so small it hasnt been an issue as of yet. And I'm using a press.
It seems to be for me that it happens in areas where part thicknesses change, its happened more around the perimeter of my boards than inside

Yes, both sides, slow WS epoxy.

That's what I'm after. Is anyone doing it with a vac?

Would using a press help?
My press is finished, I'm just finishing off other items like my heat blanket control box etc. You are in the same city as me and are welcome to use my press if you want to try that.
We would need to make a mold though.

Cheers for that. Yep, a mold definitely. Might try something different first.

Air will still get trapped using a press if you dont bring the pressure on progressively to swueeze out the trapped air. Kind of difficult to do

Yes, I think so too.

I did have a prod. clear wood board with a channels and topshets with almost zero air trapped, so it must be possible to do somehow.

The kite board surface is heaps wider than a snow board.

And concaved (3-5mm), plus rockered (35-40mm), board which makes extremely difficult job for a topsheet to lay with a hand.

Now, the other idea might be to drill the core first with a tiny holes, sort of like a perforated core to enable the air going out. I would need to build it from the bottom up, tho.

But the above board did not have any visible holes at all. Duno.

Would resin infusion work somehow under the topsheet? On such a big area?


D.

[gav wa]

Are you pressing your boards upside down?

What material is your topsheet?

Is it the base or top of your board that is concave?

[dbabicwa]

Are you pressing your boards upside down?

What material is your topsheet?

Is it the base or top of your board that is concave?

I do it in two steps, the top first and than the bottom next day or so.

The topsheet is Scorp Duraclear corona treated gloss. I do have some Crown Durasurf mat, 33cm wide if u interested. Not wide enough for me. Got SS inserts too, 8mm high, rounded base.

The bottom is concaved, that's the waterline with a topsheet.

D.

[MontuckyMadman]

the surface has to be super smooth. pre seal and then sand light 400 grit and clean then press = no bubble.