Layup techniques to eliminate bubbles under clear top sheets

[deepskis]

Have anyone tried to put a very thin layer of fiber glass (80 grams) between the veneer and the topsheet? Ads som weight but I think it would look just fine.

[petemorgan(pmoskico)]

Maybe the cores are creating a concave surface during pressing. and with that concavity, the bubbles might gather towards the center of the board. your boards are probably flat going into the press, but maybe the edges and vds and hard plastic sidewalls are creating a concavity in the middle of the board, just by having a more dense material on the outside of the ski and less dense wood on the inside.

lets say for example that everything was perfectly flat, and there was no concavity , then the bubbles wont go anywhere, and they will stay in the middle.
i think you might need to design the cores to be slightly convex so that bubbles have an escape route.

i get bubbles when i do veneer inlays, but i am not using a clear plastic top sheet so I can always sand my bubbles down and then a finish coat of epoxy will disguise them.

[Jekul]

I'll throw my hat into the ring.

At one point in my career I helped design a 2 ton heated laminator for web to web converting machinery. We had similar issues when we pressed our top and bottom substrates perfectly flat. The bubbles got trapped in between and had not way of escaping.

I'm not sure how it would be done on a press, but if you could apply the pressure from one end of the board/ski to the other, you may be able to effectively "roll" your bubble out with your air bladder, and not have to worry about air creeping back in before you press.

[Toddh77]

I was having the same issue for a few tries. I had Troublemaker build me heat blankets, now my topsheets are coming out perfect without any air bubbles. Heat was the answer for me.

[jellyfish]

I would try the thin fiberglass layer between the two hard sheets, I would also flip over The top sheet and lay it up separate with the thin fiberglass on it and then flip it over and place it on the wetted out veneer.
Also try sealing your veneer if it's dry, lot of problems out here with veneers that are too dry and they expand as they get wetted out. So if you try and just paint thinn epoxy layer on it to seal it it warps all over the place so I was vacuum bagging to a large sheet of glass and curing a real wood knife cut 1/32" veneer top sheet last season with a layer of super white surfboard fiberglass ok results when I used lighter colored wood you had to look very hard to see the tiny bubbles but when it was a dark wood it was obvious, best results, was by accident when I precured a sheet with a thin glass it failed so I flipped it over and sanded it, it was wavy, I got it smoothed out the thin glass held it together, then I precured the other side with the super clear glass and it turned out perfect it was a week of hell.
I think it you got the thinnest flattest sealed veneers possible you will have the best results, I think the tiny splinters of wood (like hair) cause the bubbles.

Cheers
Jim

[petemorgan(pmoskico)]

i think a couple folks said this now, but i will echo it:

I believe that it is the ramp up that is causing the air bubbles. You are most likely ramping up too quickly to your cure temp and thus the resin is starting to cure before all of the air has time to escape, thus trapping the air inside.

I believe that if you make your ramp up cycle slower it will fix this problem of bubbles

(although maybe the firehose method of ski building will inherently have air trapped rather than vacuum bagging which sucks the air out. )

[astroskidder]

I am running a test that I will post an update on once I get some results...

Using 8210 and laminating it to a paper backed wood veneer as a first step, basically creating a wood veneer prepreg to use in the layup process. Buttered the top side of the veneer and the bottom side of the 8210 and used a 6 inch epoxy squeegy/spreader to push the air bubbles out towards the side... once I was happy with the look, I set it aside to cure.

My plan is to then use the above as the final topsheet during my layup. The paper backed veneer will be buttered and laid down over the final layer of glass and then the ski pressed as usual.

Don't see any reason why this should't work, but I've been wrong many times before.

[COsurfer]

How are you going to keep the 8210 from popping back up? the 8210 I use curls on the ends and side. As soon as you squeegy it, it pops back up.

[twizzstyle]

Maybe vacuum bag the clear top to the veneer? That will keep them pressed together, and the reduced pressure will help the epoxy out-gas.

[COsurfer]

Just tried that yesterday and it didn't work. U have to put a breather fabric above the 8210. Can't see the bubbles to get them out.

[twizzstyle]

Put the breather under the veneer, duh

[deepskis]

...or put a mylar film on top of the veneer and skip the topsheet. You will get a mirror like finish

[astroskidder]

The first step went well. No problem seeing the bubbles and working them to the edge of the 8210 with the squeegy. The assembled veneer and 8210 has cured and can be formed to any shape, but is quite more stiff than either product on it's own.

Next step is the actual mock-layup... more later.

I am running a test that I will post an update on once I get some results...

Using 8210 and laminating it to a paper backed wood veneer as a first step, basically creating a wood veneer prepreg to use in the layup process. Buttered the top side of the veneer and the bottom side of the 8210 and used a 6 inch epoxy squeegy/spreader to push the air bubbles out towards the side... once I was happy with the look, I set it aside to cure.

My plan is to then use the above as the final topsheet during my layup. The paper backed veneer will be buttered and laid down over the final layer of glass and then the ski pressed as usual.

Don't see any reason why this should't work, but I've been wrong many times before.

[COsurfer]

Put the breather under the veneer, duh Smile

Ya Duh, WTF was I thinking! Brilliant Twizz

Deepskis, have you used mylar? is it durable?

[deepskis]

Deepskis, have you used mylar? is it durable?

Yes, I have used it a couple of times and it gives you a very nice and shine epoxy finish. No need for varnish on top if you dont leave the skis outdoor for a long time. If you want to you can screen print on top of that and then put some varnish on. Looking good.