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Plywood and cork

Posted: Mon Aug 20, 2018 5:53 am
by zensuni
I have a new project in mind.
I would like to make a plywood board that would minimize the inherent plywood boards flaws.
Which are, to me, the lack of buoyancy, and these dangerous hard edges.
So, my plan is to make a sandwich:
- the bottom layer will be a 1cm plywood sheet, the same one that I would use to make a basic ply paipo.
- for the middle layer, I would use 1cm cork isolation sheet.
- the top layer would be a 0,5cm plywood sheet.
I will glue the layers, I don't know yet what kind of glue to use.

The cork will add some buoyancy (very little but I don't want too much either, I like easy duck dives).
The cork layer will be a little wider and longer than the plywood layers, so it will exceed like 1cm around the board edges. So it will be a cork rail, this is for safety.
Another advantage of this sandwich construction is that it will result into a ticker board (not as tick as a bodyboard though, only 2,5cm), that will provide a better grip.

I will update the thread with photos.

Re: Plywood and cork

Posted: Mon Aug 20, 2018 9:30 am
by zensuni
Another annoying thing with regular plywood paipos is the fragility of the edge. Mine keeps to get dings on the edge, I always have to re apply some varnish to fix it. I hope the kork edge wil help with that.

Re: Plywood and cork

Posted: Mon Aug 20, 2018 2:34 pm
by zensuni
Another option would be to replace the cork sheet by this recycled rubber sheet: ... 1400791687
Less natural for sure, less buoyant, but maybe more resistant ?

Re: Plywood and cork

Posted: Tue Aug 21, 2018 11:17 am
by GeoffreyLevens
I think having the plywood on the outsides of the sandwich, you may still have pretty darn hard edges if/when they impact your body. I do like the idea of experimenting with sandwich construction using easy to source materials!

Re: Plywood and cork

Posted: Mon Aug 27, 2018 5:54 pm
by rodndtube
I will try to have PhillyViking reply. He has been working some materials along with cork and the adhesives.

Re: Plywood and cork

Posted: Mon Aug 27, 2018 7:37 pm
by asier esnal

Re: Plywood and cork

Posted: Mon Aug 27, 2018 9:12 pm
by PhillyViking
I have been in slow-mo on a cork core project with each step weeks and even months apart. I will give a full report when I actually finish sometime in this decade. I was initially going to use titebond III to adhere cork to paulownia ply but the titebond manufacturer I called raised concerns. I turned to Entropy Epoxy that does bind. I have been doing one layer at a time because I did not know how much epoxy to use and I made a mess of my one shot at all layers first attempt. I can now eye ball it but neglected to keep records of the epoxy weight.

I was trying to get more float with cork than solid wood. I ride a wood board today. However, using a vacuum bag and the density of cork I used, I wonder whether the saturated weight of the cork might end up weighing as much as solid paulownia ( I still have one layer to adhere when the stars align and then .. finally shaping). The possibility of more weight than expected was reinforced when I came upon someone with a Bodypo (cork with internal fiberglass layers). I was surprised at the weight when I picked it up.. It was only promoted as having neutral float. At some point I will weigh some comparable sized boards and report to the forum.

I am using the vacuum to clamp the layers against a mold. In this iteration I will end up with a blank with rocker and some shape but I will still need shaping of rails and channels. In theory you could mold the final shape.

It appears that most builders using cork do saturate the cork with epoxy. That keeps it solid. I see that many then sand off the top most part of the skin so that they do not need to use wax. If you use low density cork you end up soaking more epoxy into the cork. If you use high density cork you get less epoxy infusion but more cork weight. I wonder if I could keep the weight down by sealing low density cork without vacuum first so that I do not get as much epoxy saturated into the cork. I could then vacuum that with ply or cloth layers. Maybe only the skin of outer layers need saturation?

Cork as a soft thin skin over other materials is a different discussion than cork as the primary core. I still think cork is a viable core alternative. I am just saying that it might not end up being a light as you expect. One way or the other you need other material layers to stiffen it and you need some some epoxy weight to adhere the layers and to keep the outer most skin intact.

I would love to hear from others going down the cork path.

Re: Plywood and cork

Posted: Tue Aug 28, 2018 10:28 am
by GeoffreyLevens
I have never worked with cork but might be you could seal it and prevent a lot water weight from saturation. Squeegee on so super thin, multiple coats of....something, epoxy perhaps. That might act like the spackle cheater undercoat used when glassing EPS foam to prevent the resin from running all the way through and adding lot of weight. That I have done and it dramatically reduces the amount of resin soaking into the blank. Urethane varnish might work as well.

Re: Plywood and cork

Posted: Tue Aug 28, 2018 3:14 pm
by PhillyViking
I guess I could think of this as fairing as in wood boat making .. smooth and seal.

Re: Plywood and cork

Posted: Wed Aug 29, 2018 4:49 pm
by krusher74

Re: Plywood and cork

Posted: Mon Sep 24, 2018 3:56 pm
by PhillyViking
As I said my board with a cork board core (not just skin got heavy).

I circled back to what should have been my first step .. what are the relative densities of materials?:

200 kg/m3 for NL-20 ... ecork.html

280 kg/m3

EPS Foam
2 lb/yd = 0.99 kg/m (I hope I used the correct conversion)

My 50" x 20" x 3/4" cork board ended up weighing 10lbs 7oz compared to my 48X18x1 1/4 paulownia board that came in at 7lb 6oz. Not exactly an apples to apples comparison but I think the point is the same. I might do the actual comparison math later but it seems heavy. Cork starts out lighter than Paulownia but absorbs a lot more resin. As executed, there was no compelling buoyancy benefit to the cork compared to wood.. That was part of my motivation.

A lot of the core cork builds I see in retrospect use templates more like foam body boards but thinner than my build.

In principal I can get some weight out by fairing the cork to seal it against unwanted infusion of resign but that might also make the bond weaker. I could also use unidirectional flax instead of woven flax fabric. The woven flax even with a vacuum took on a lot of resin. The unidirectional that I will use in future projects lays flat and absorbs less to get the same results. I can lay perpendicular layers if I need strength in both directions.

I was able to mold the cork core to get a bit more rocker than I have in my solid wood boards and I also got the right amount of flex compared to my more ridged wood board. With wood you either need to waste a lot of material or do so some splicing to get my target rocker.

Re: Plywood and cork

Posted: Sun Sep 30, 2018 11:07 am
by Atlantasurfer
Do you have any pictures?

Re: Plywood and cork

Posted: Tue Nov 20, 2018 6:26 pm
by asier esnal
I'm interested in this conversation. I am planning different ways of manufacturing very fast and cheap that allows me to try different paipos

the corecork is a fantastic material. It disperses the energy of the blows avoiding damage to the board but maintains flexibility. if you put EPS boards with fiberglass and corecork they are important

weight. That is your big problem. It absorbs the same amount of resin as its density. a Cork of 250 giving it epoxy can be put in more than 400. a barbarity. That happened to me 3 years ago when doing an EPS board. poor choice of materials

I'm thinking of 2 thin 2mm birch veneers one on each side. in the middle xps. there will be a delamination problem but since it does not absorb water, it is not necessary to throw a perfect seal

I do not know how to make rounded rails very quickly. with just this recipe the rails come out square