The resin does soak in the cork. So insticntively the idea of getting the lightest density cork(nl-10) you would come away with the lightest final product. But you actually get the lightest board with the denser NL-20 because it soaks less resin.
The tricks to a light board is start with a light core, use a 2 oz or 4 oz glass layer between cork and foam. I only have been using 4 oz cloth on the final outside glassing. It is sealed from the inside out and then glassed like a regular surfboard with 4oz cloth. On two boards I used pull-ply during the initial corecork vacuum bagging and was able absorb unecessary resin successfully.
The most suprising discovery was the unreal flex acheived when a did a PU short board with the corecork. The EPS locks up with the stuff but I am talking FULL range of motion flex with the PU blank. I finished two boards last Friday I will send pics of. I know I can get way lighter and am getting there slowly.
Drewtang from FL is the expert on this site with the stuff. He probably has the best advice on corecork.
I still see it taking off in board construction in the future.
I dropped in on Drew a few years ago and visited his shop when he was first getting started. Straight up guy. Very generous with the knowledge. Drew, if you are reading, good on ya.
I only use epoxy resin. normally 4 oz e glass wetted out on the cork, flip to foam side and vacuum. The EPS locks up but the PU is very flexy as in one foot push down will make it flex. The eps is stand on the board with both feet and bounce tight.
also my final outside cork lamination is 4 oz E glass. 1 layer on either side.
Regular surfboards have the PU with 1/8" wood stringers and the EPS have a 5lb, 1/8" high density foam stringer. EPS tow boards are stringerless, 2.5lb foam. with wood and 18 oz of cloth on each side.
paulownia is hellova lot stronger then balsa and im pretty sure balsa is stronger then cork. paulownia has benefits of cork with a better tensile strength. as far as i know cork is used spareingly if at all in dynamic load bearing composites for this reason. i think it would be good for rails tho.i was under the impression it is a similar density to paulownia with far less tensile strength. anyone got any figures on its tensile strength mode of rupture
as far as i know cork is used spareingly if at all in dynamic load bearing composites for this reason.
Hey Paul, with all due respect, I think you're a little misinformed. I don't have scientific numbers in front of me, but I'll give a practical argument. You can't just lump corecork in with "cork". This is a problem as guys routinely try a roll of corecork and then buy a much cheaper roll of cork underlayment, or cork for bulletin boards, and their parts fail. Amorim has a proprietary process to make corecork from raw cork bark into product, it's a little over my head honestly. As far as dynamic load bearing for composites; burton snowboards has been a customer of core composites for 20+ years. They have switched all of their cores from balsa or coremat to cork, commiting to more rolls in 2012 than we (surfboard builders) could probably all buy combined:) Searay boats is one of our country's largest builders. They have scrapped all coremat in their laminates in favor of corecork. Once they began with the cork in their laminates they began putting the thicker (3/4") corecork in hatches, eventually even stringers and bulkheads. Corecork when used in a laminate schedule has similar properties to hd pvc's with no water absorption, fire retardant, sound and vibration dampening, and huge cost reductions. I'm not just soapbox preaching, the stuff is legit and it's just the tip of the iceberg. You wouldn't beleive how well it's been accepted into windmill turbine composite construction (with some weird unexpected benefits regarding moisture inside their motors?). The windmill thing is huge, and the reason why I'm waiting on a new shipment of cork right now, I"m out and the new product is a few weeks out on the boat:(
One other point for corecork, this is just from a personal opinion, is sustainability. You're also comparing with woods that have to be harvested. To produce corecork, they just skim the bark and no harm comes to the tree. I know this isn't much of a valid point when comparing strength and loads in a composite, but you have to cheer for the greener product as a surfer, don't you??
Thanks for the kind words up here guys, I'm always a phone call or pm away if anyone needs any help (as much help as one hack can be). ps Greg Tate, that was fun when you came by, you should come over more often (but I wasn't just getting started, that was like 07, I got addicted to this hobby/career in high school, 94, man I'm old).
thanks BB30, I’ve been doing stringerless EPS with 4oz sglass over a cork deck with 1.5 oz under the cork. The flex is pretty good, but i’m probably shaping my boards a little on the thicker side. I’m getting about 3-4 inches of flex with the very scientific foot in the middle of the board test. I’m going to have to try an epoxy over pu board. I’ve been thinking about doing suncure poly, but keep resisting-all those fumes.
hi Drew, im not denying its useable i just said its tensile strength is far less then paulownia. i wouldnt use it in a hull of a boat or a deck. hatches yes, bulkheads if your crazy. paulownia can be used in hulls. i was reading the pdf from corecork and it neglected to compare tensile strength to wood cores . wood cores have far greater tensile strength. thats all im saying. if anyone has data to prove otherwize go for it. i would say cork would work well as a dampener. i think that would be why i would use it on eps cores and also its water resitance properties are favourable. paulownia absorbs water .
now real world testing of pvc cores. pvc over eps boards with pvc rails will still snap prettty easy. if you do one skin in wood other pvc the rest of the board will snap but not the wood. if you do both skins in paulownia i have no evidence of one having been snaped to date. if anyone can has a snapped paulownia skined board with a core of at least 3mm could they please post it here. the corecork pdf shows cork having a slightly higher tensile strength to pvc. so i would consider using it on the rails or for a fast clean build. but it would not be superior to paulownia as a core for the the reason that vertical grained paulownia is far stronger.
huie is gunna send me some so i will try it but i dont expect a snap proof board like i get from cedar and paulownia
Right on, im following. Just do some test panels with huies stuff and I’m sure you’ll be stoked. I built hundreds of bamboo skinned boards before corecork fell in my lap. Still do plenty of bamboo, stuff is hella strong, also hella stiff. Honestly didn’t put any bamboo skinned boards under the foot of a"better" surfer without stiffness complaints. Average customers no problem, they are beautiful and bulletproof, and will always be valid. No experience at all with paulonia, don’t even think I spelled that right;) just keep an open scientific mind when you build your test panels. Its a dream material in my opinion. Solved several of my problems… I needed a flex neutral sandwich core lightweight, water tight and cost effective…check that off the list, now give me my carbon innegra braided tape…(oh wait, its in the mail!!! Yyyyeewww)
Edit and add;
Want to say real quick that I’m quick to dismiss any claim at “figuring it out”. corecork is really radical, really new, and really “now”…but so many builds skin the cat. Wood skinned, hollow wood, pvc, whatever the hell those twins are doing, etc… All valid, all sick, the only real fear I have is settling down with one build. For me, bamboo on certain builds, cf framed on some, perimeter stringers and dual densities still in play after a quick shift in"popularity, corecork for me is cream, works on everything and I can think of at least a dozen valid builds with the product. Its in the right hands now, soo fun to sit back and watch; this is still a voyuer site, correct?
Cork is a really good damper for sandwich material for panel that experiment dynamic compression constraints perpendicular to skin. It was use for that in european aeronautic buiding in last 70, came from a factory in south of France. I see some sandwich panel test made in R&D lab, they not really found similiar results but we don’t know how are made samples… If you look to corecork sandwich mechanical propetries in their pdf, you can see that cork sandwich panels have more or less same results than pvc panels, but cork is 2 to 3 time heavier ! if you do same test panel with 140kg/m3 cross link PVC no compare possible for stiffness and flexural strengh.
But for our surfboards we don’t want stiffness and flexural strengh is not the problem. Board skin break by buckling, the main properties of skin against buckling is toughness. Dampening properties of cork is a really good thing to add toughness to a sandwich panel. PVC foam core panel have low toughness. In KCU test i can see that best results ratio toughness/weight were for sandwich with wood core, and i understand why Huie say wood is the best fiber for him.
That’s why I like the cork- still allows the board to flex, but provides impact resistance. I hadn’t thought about the dampening aspect, but I wonder if it would help epoxy boards with the weird feel that turns dedicated poly riders off to them. I’ve only done the cork on the bottom of one epoxy board, not enough to really tell.
As far as weight goes, my cork boards are coming in a little too light for my taste. I did a gloss coat on the last one for myself just to give it a little more heft.