Unfortunately your bottom layup is sandwiched between 2 hard surfaces and a sealed pathway your going to end up with bubbles, I don't think temp has anything to do with it it's lack of force to move the resin, squeeze out the air.. Wood core is cheaper but a core cell core won't give you bubbles when you press it in a vacuum, it will deform easier there is a reason we use bladder presses to get more force when working with hard surfaces add 180*f heat and everything moulds together. So perforate your core do the bottom first breather on top while stuck to the bottom mould do the top and hope for the best.
PV=nRT a gas? temperature always involved. Don't believe? lay a sheet of wet fiberglass over a porous substrate. Cure in rising temp - bubbles every time. Cure in falling temp - never bubbles unless you have poor technique (excessive exotherm etc.) If you get good at it, glassing a slightly porous substrate in falling temps can give results equal to most vacuum bagging jobs as air in substrate contracts sucking resin and fiberglass down to the core surface. >50% fiber:resin can be achieved.... Want to cure at higher temp? Make sure you have got rid of the air first! Or seal the substrate carefully before lamination!
I never said you were wrong I said I do not think the temp rise from curing marine type room temperature cure resin is enough to cause the bubbles on a wood core in a vacuum layup and then I offered a method I would use to eliminate this problem. I am not here to argue with you. I never have this issue I take the laminated wood core board from room temp to 180*f to cure the resin,,, no bubbles no troubles. Now that is a rising temp on a Porus wood core with air trapped in it , it just an extreme example. Basically the air cannot escape as you describe in a vacuum it would have to have an integral pressure greater than your vacuum acting against it to allow it to pool out of the core into pockets under the glass and the bottom of the board, i believe that the air would act equally inside the core balancing with equal force My point is the air was there when you put the core down you just could not see it it was a fine layer or many small and large pockets of trapped air on the surface of the board and they could not escape. It would not be air from inside the boards core there is minimal air in there and it would be trapped and so tiny. Its wood it has a density So solve the problem by giving the air pocket an escape route and they will its what they want to do you just will not let them. If you can see air bubbles on the top when not using a breather and they are air locked you can squeegee these to the rail and they will disappear , too bad you cannot squeegee these trapped pockets out from the bottom surface
depending on your method there is tricks to solve most problems. Not everyone does things the same there is always a better way.
Hand layups are a different story but that was not the question was it.
Not a smart man... All good feedback and I think pointing the right direction for success. I started this process a couple years ago just reading all your post before I jumped in the game. And was not sure why the bubble problem was happening when it seemed no one else really had it. Agree that it is a matter of getting my own system down a sticking with it once I find a method that works with my set up, using cedar because I like the strength, looks and it is cheap here in the PNW. I will increase the shop temp, use perfply in stead of peel, seal the core prior to layup, try it once with breather and perf on bottom and hope for the best.
Agree with Peter that the air was getting stuck between the table and glass when I have tried to do it all in 1 shot, then I went to a 2 shot layup and had air under the glass. But really want to accomplish things in 1 shot. I have always felt the air gets trapped when the board is going from straight to profiled under vac. I was using cheap 4 oz E and have switched over to 6 and 9 oz S glass to stiffen up the center of the board.
Jim - I think things are getting trapped between the plexi and core - so i will try perfing the core for escape to the top side.
Is there a preference for resin brand with you all? I have used resin research and west.
Hi guys, I just want know if any of you have an issue with some sort of micro air bubbles which makes the glass fibers whitish not trasparent in low thickness laminates? I guess it could be related to a relatively high pressure applied by vacuum bag. There is no whitish fiber issue in atmospheric pressure setup, but when i apply a high vacuum it will tend to get whitish. Is it a common issue for high compaction ratio and low thickness (50-80g/m2) glass laminates? Or there are some tricks to get a nice quality transparent glass layer under high pressure?
Hollow wrote:Hi guys, I just want know if any of you have an issue with some sort of micro air bubbles which makes the glass fibers whitish not trasparent in low thickness laminates? I guess it could be related to a relatively high pressure applied by vacuum bag. There is no whitish fiber issue in atmospheric pressure setup, but when i apply a high vacuum it will tend to get whitish. Is it a common issue for high compaction ratio and low thickness (50-80g/m2) glass laminates? Or there are some tricks to get a nice quality transparent glass layer under high pressure?
To avoid it you need to degas the mixed resin at a pressure lower than what you are using with the bag. Or you could give it max vacuum at first and then dial it down so that the bubbles compact once again. It is most likely just some micro air bubbles from mixing that get expanded due to the vacuum.
Quick update. I did lay the board up in one shot, did use breather on the bottom, and in general things worked out. Had some air leak issues with my vac bag connections (never had that before), and overall really like the ride of the board. Made and error on the profile table and the core was too thin near the tips, so I put a layer of triax near the tips to made up for the lost thickness of the core. Have some dry spots in the glass (lots on the base), I think mostly due to the fact the resin was kicking before I was really ready. In a nut shell, 138 x 43.5, board is really light (sorry no measurements as my friend has it now), 2mm of concave, lots of rocker and rides super smooth. Need to be more patient with my hot coats and sand more. I have two more cores ready to profile and will be laying up one side at a time to hopefully manage the dry spots better. Thanks for the advice - hoping to continue to dial in my process. Couple of photos of "The Otter" if you like.