Hi there! here are pictures of my last ( fifth) board... I'm not happy with the results ..there is air between glass and wood core on the bottom
here is the lay up
rocker table
epoxi-glass
wood core ( cedar)
epoxi-glass
vacuum bagging sistem

What do you guys think I did wrong? what shouldI do to avoid having this problem again ?

I dont think the glass was dry , may me if I lay the glass on the bottom of the core and then put the core on the table would change something?

another question is it the same to glass one layer of 18 oz than 3 layers of 6 oz?? I ask because I have a roll of 18 oz glass sitting here and I can give it good use!!

I'm open to suggestions!!!

Thanks in advance for all!!

You get air bubbles because you didn't get enough negative pressure at the right time in you bagging set-up. That can be down to many things.

1. Epoxy too viscous, didn't wet out the core of glass fully.
2. Not enough pressure to form the core to the rocker, could be a leak, crappy kinked rocker table, or insufficient vacuum pressure.
3. Too much vacuum, you crushed the wood core releasing bubbles into your epoxy and this happened too late in the set for them to migrate to the peel-ply and breather absorber.
4. Too damn hot, your epoxy set-up before you achieved sufficient vacuum.
5. Any variation on the above would do it as well.

These are all things I've seen when bagging.

My advice would be. Check your pump, rocker table and consumables and use a slower set. Think about when you bag as well. In the summer try to do it as late as possible for longer working times.

best of luck.

Thanks for the advice . It's a lot of new variables againg for me to start checking. Hope the next one comes out right !!
Thanks again!

sq225517:I was just thinking after reading your reply. I did run my vaccum pump at 22.5 hg for a few hours until the epoxi was set. it fell hard to the touch so I knew I couldn't get anymore epoxy out of the system. Turned it off and left the weights on top of the rocker table-board...until finished curing, may be I did it too soon?
Do you think 22.5 is too much or too little presure for a cedar core?
Thanks again for the advice

I've never built with wood cores, only nomex and Airex.

simon may be right.
he has enough of the variables covered, so its likely to be one of them.

however my opinion is that you can never generate enough vacuum to damage a cedar core.
cedar is quite stiff and in all likely hood you are not able to generate enough differential pressure to force the core completely onto the rocker table.
despite its flexability it will not completely conform to the rocker bed as most plastic cores would.

i'm assuming you really have a bubble under the glass and not just a dry lam.

if your procedure was to wet the glass out onto the table instead of wetting the glass onto the board it will be difficult to get a good layup.

what you are suggesting is close to ski or snowboard construction where they force the rocker into their core with 100s of psi ( not 14) by using a press.

i think you will be better off wetting out both sides of the board (or one at a time , if you prefer)but use a full bag layup around the board .
then use clamps or weights to clamp entire assembly to the rocker table

regards,
-bill

ps:
cedar is quite strong, so w/o knowing any of the details i would be surprised if you needed more than 4 or 6oz per side to get the strength and flex you are looking for.
a small test piece may be in order if this is still a variable for the final layup
(never mind, i'm sure this board will answer that question for you)
but to answer your last question :
3 layers of 6oz will be very close to 1 layerr of 18oz assuming similar weave and orientation.
the 6oz cloth will probably have smoother finish due to the finer structure of the weave.
the 3 layers may use more resin, depening on your lam procedures and how much you need to fill coat the relatively coarse 18oz stuff

Bill, you are very close to the way I think about what happened here. I think I had not enough vaccum to force the core into the rocker table and glass, even having weights on top of the core when vaccuming.
My glass lay up was on the rocker table ( I have done it before they way you say with great results ) and I think no matter how much weight i put on top of everything the core wasnt goint to contour exactly to the rocker table

next time I'll do what you suggest of using a full bag with the glass lay up on top of the core and clamp it to the table

Thanks a lot you guys for sharing info !!! I love this forum!

Bill
the board on cedar has only one layer of 6 oz glass per side and reinforcements on the inserts
I was asking for the 18 oz glass because I have a roll of it and I can use it with balsa or foam cores I believe. It is a shame to have it sitting there till it go to waist.