Hi,
Doing some board mods (extending the deck for foiling) and the board is a super nice carbon/glass sandwich so I want to do the mod fitting with the board.
Where I live, divynicell or other pvc foams are expensive and expensive to ship. I've used cork for other projects but it's a bit heavy. I'll probably be doing the extension out of xps (eps is another foam that's hard and expensive to obtain for me) and pour foam. I'll be vacuum bagging things and have regular glass, S glass and cf at hand.
Am I overthinking things and just do a layer or two of cf with a top of 4oz glass? Or, go ahead and use the cork as I've done with other extensions? Or, just suck it up and order some PVC foam?
I live far from the ocean so running down to the local surf shop for cutoffs is out of the question.
Select to expand quoteImax1 said..
Where are you , how much do you need ?
States, thanks for even pondering it, though. 
To answer your other question, a total of probably 1m2 either in one piece or two pieces.
Select to expand quoteaeroegnr said..
Was just curious and saw fiberglassflorida has 1/2" sheets of 4'x8' at $165.
Shipping something 4x4 will bring it up to around a couple hundred. But the real issue is that it's too thick. Looking for 1/8 or 3mm thick. Thanks all the same. A good thing about the thinner PVC is it can be rolled a shipped a bit cheaper.
Yeah thick stuff gets pricey. If you're mucking around with stuff like filling up cutouts and glassing over, offcuts of surf blacks (about 2.5lb polyurethane) is great.
Or for flat, end grain balsa - just don't let that get wet.....worse than styro
Third choice XPS (blueboard, building grade stuff) but it can have delam problems if not treated right - for experiments it is great and $20 not $100 like PVC foams
What do you mean by extending the deck though.....?
Select to expand quoteMark _australia said..
Yeah thick stuff gets pricey. If you're mucking around with stuff like filling up cutouts and glassing over, offcuts of surf blacks (about 2.5lb polyurethane) is great.
Or for flat, end grain balsa - just don't let that get wet.....worse than styro
Third choice XPS (blueboard, building grade stuff) but it can have delam problems if not treated right - for experiments it is great and $20 not $100 like PVC foams
What do you mean by extending the deck though.....?
Widening deck from front straps back for foiling.
My current project - cork sandwich over xps foam. Same board in both pics Nose also got bobbed a good bit. Mast track and strap inserts moved, too. Probably would have been cheaper and quicker to get a job flipping burgers to pay for a new board. 
Edit: just reread your comment and realized how to make blanks to fill in us boxes! Thanks! 
What density xps? If it's around 40 you can probably get away with layers of carbon.
Well I wondering if a carbon glass carbon, sandwich would work.
Now I see what your doing, compression resistance is key, bonding to deck is key, but tensile strength and rigidity etc not so much as the board is already doing all that work
As you are vac bagging (big advantage)
I would go leftover surfboard blank foam glued on with a layer of glass and resin/q-cell mix. So far its free - offcuts. And its magic to shape compared to EPS or XPS (yuck, tears. Ugghhh)
Then laminate with a wood laminate (I use 0.6mm pine like all the WS board manufacturers as at 500kg/m3 its the same as 3mm 80kg corecell when you do the math) ..... and also some fibre.
So on the shaped foam
1x 4ox glass
2 x 6oz carbon or CK of any variety just under the feet
1x 0.6mm wood laminate
1x 4ox over all the additions and deck to tie it all together.
That would be like a surfboard deck with wood and carbon added - I do that kinda lam on kiteboards and they don't heel dent. So for a non-slapper WS board, it will have enough rigidity. And cheap!!!!!
As an aside - maybe it is still better done with a PVC foam like divinycell. But is the cost of the thick stuff to make a big higher/wider rail so I think you should do cheaper.
But - I don't do PVC foams anymore. Corecell is soooooo much better
Heat forms better
same compression resistance
same density
less brittle so less cracking when vac bagging around a rail etc
and the best of all - longer elongation at break - so it bends further before snapping and that's what we want. All the physical properties are the same but the thing can take a lot more deflection before it busts.
Still use big chunks of dicivycell / airex / herex for mast track and fin installs but for a sandwich all over, corecell M80 is the shiznit.
Thanks, guys. Leaning towards wood veneer since it's a lot cheaper - Full 4'x8' sheet for $120 shipped so I have plenty left over for woodworking projects. Found a half sheet of corecell in the States for $80. Shipping is $120... At my weight, though, decrepit's suggestion of glass/cf/glass is tempting as both light and easy.
On the current build, I shaped the xps to the board edge, glued with pu and then filled the gap with 2 lb pour foam which is quite adhesive. Shaping the add-on to the deck is too complex for me. The glass both under and over the cork tied it to the existing deck and rails. I ended up using more bog than I should have because I didn't extend the foam or cork far enough and then got OCDish about blending the joints nicely.
Appreciate all the input.
Wow I'm normally p!ssed at how your prices are so much better
8x4 wood veneer is about $60 here ($45USD?) and rolled up with a courier taking it 400km might make it up to that price .... maybe...
Try any local woodworkers as you will only need a couple bits 3ft x 1ft..... ?
Select to expand quoteMark _australia said..
Wow I'm normally p!ssed at how your prices are so much better
8x4 wood veneer is about $60 here ($45USD?) and rolled up with a courier taking it 400km might make it up to that price .... maybe...
Try any local woodworkers as you will only need a couple bits 3ft x 1ft..... ?
Oh, my bad for being unclear. That's the price for corecell (and similarly divynicell) thus prompting my original post. Veneer is cheaper by half and about the price you are seeing there. Already scouted out some on ebay.
btw, is a paper backing a deal breaker? Seems pretty common for furniture grade veneer. I was assuming the resin would soak through and not really matter.
Again, thanks for the help. The posts the pros like you and decrepit do inspire the rest of us to get our hands dirty and try stuff. If nothing else, it gives us a better appreciation of the craft.
no backing I don't trust it. clean no glues or backing which here they call lay-on veneer
+1^
Glue under the paper is probably soft, allowing the timber to slide around under side loads. Epoxy probably won't stick to it if it does soak through the paper. It may work or it may be a disaster.
Select to expand quotedecrepit said..
+1^
Glue under the paper is probably soft, allowing the timber to slide around under side loads. Epoxy probably won't stick to it if it does soak through the paper. It may work or it may be a disaster.
well and i just realised too that when vac bagging, the resin is drawn thru the wood in the softer parts......... the glue would likely inhibit that
A bit more on a carbon glass carbon sandwich.
The suitability of this this would depend on your foam density. The last time I looked the lightest xps available was over 30kg/m2^, I think that would be OK.
I wouldn't try it with 13kg/m2^ eps.
I'm no engineer, so can't work out the exact numbers, but I have used xps for windsurfers. On one I used 3 X 6oz glass only on the deck. It was too soft, but not by much. I used the board like that for several years.
I'm fairly sure the extra stiffness of carbon would be good. However not so impact resistant as a glass wood glass sandwich.
If you already have the carbon and glass, that would cut your expenses considerably.
But only use it if your xps is high density
I was curious and just looked up shear strength numbers, which was what we were concerned with in certain reinforcements...
Low density eps is roughly half the shear strength of ~28kg/m3 xps. Looks like compressive strength tracks similarly. Divinycel at the lowest 38kg/m3 looks similar in strength to that xps, but you can get much higher density stuff in grades up to 250kg/m3, which has about 10x the strength. I just searched briefly but I didn't find good compression modulus numbers, which is the stiffness of what you'll feel under your feet.
Balsa is a lot stiffer and stronger than the typical foams from the look of it, but it really depends on the grade. These aren't materials I'm super familiar with but that seems to line up with what you guys are saying.
What about balsa wood?, and not end grain, but a sheet of balsa wood, usually thin, cheap on Amazon, see up to 12"x18"x1/8", 6 sheets for $35.
Yes, it works well, but hard to bend round the rails. You need a different technique if you want nice round or oval rails.
And if it gets wet it will rot.
What we are after for the center of the sandwich is compressive strength, the outside fibers give the tension strength
Select to expand quoteSandman1221 said..
What about balsa wood?, and not end grain, but a sheet of balsa wood, usually thin, cheap on Amazon, see up to 12"x18"x1/8", 6 sheets for $35.
I can't see sheet balsa is any use when he wants to build a structure with some thickness - up to about 2" at the thickest.... would be heavy AF and no compression resistance compared to end grain balsa or foam in a sandwich.
Difference between doers and theorisers.
I await the suggest about Six10 epoxy....
Sheet Balsa will not give you the compression resistance. It's very soft. That's why they make end grain balsa. Some sort of veneer will give much better compression resistance.
Where are you located?
I don't have the experience of others that have commented but learnt very quickly trying to save money on materials is not worth it. You spend so much more time messing about and normally for a worse result.
Just looked at your earlier posts and see you are in the states. I would have thought you could get veneer easily. Maybe try some 0.6mm maple veneer.
Does the paper backing really inhibit epoxy uptake? Or is this a supposition?
I have tried clean veneer sheets and paper backed and noticed no difference. The paper appears to disappear within the epoxy a bit like decals, and it is much easier to get around the the deck without splitting.
I have only done a few boards with veneers, but they haven't delaminated. Below is my latest dyneema / veneer / Nomex honeycomb freestyle board:
Select to expand quoteOverner said..
Does the paper backing really inhibit epoxy uptake? Or is this a supposition?
I have tried clean veneer sheets and paper backed and noticed no difference. The paper appears to disappear within the epoxy a bit like decals, and it is much easier to get around the the deck without splitting.
I have only done a few boards with veneers, but they haven't delaminated. Below is my latest dyneema / veneer / Nomex honeycomb freestyle board:
Beautiful work. If only Starboard's wood boards had looked this nice especially after being in the sun a bit.
Very nice construction . I have pondered using honeycomb . After touching and holding it , one sided and double sided , I'm presuming it can only be used on a relatively flat bottom because it's so stiff ? The thinnest stuff would have problems on a slight V or concaves . The one sided stuff is flexy , but how would that go hand laminating or in a vac ?
Select to expand quoteOverner said..
Does the paper backing really inhibit epoxy uptake? Or is this a supposition?
Mainly supposition on my part, but I do have experience of a sandwich failing because contact cement was used to glue the tension element to the core. It just allowed enough movement to counteract the tension force.
I just don't think it's worth the risk.
Select to expand quotedecrepit said..Overner said..
Does the paper backing really inhibit epoxy uptake? Or is this a supposition?
Mainly supposition on my part, but I do have experience of a sandwich failing because contact cement was used to glue the tension element to the core. It just allowed enough movement to counteract the tension force.
I just don't think it's worth the risk.
Is that because the contact cement doesn't soak through the paper and into the wood ?
Select to expand quoteManuel7 said..
Local guy uses canned spray foam
I'm cheap but I'm not that cheap.
For anyone tempted, the uneven and large air bubbles inside make spray foam a horror show if you try to shape it. Get pour foam instead if a block of foam can't be shaped for what you are doing.
Select to expand quoteImax1 said..
Is that because the contact cement doesn't soak through the paper and into the wood ?
This was a totally different system, an X-ray table top. It had 10mm dense foam of some sort, with laminex bonded to it with contact cement.
Heavy patients on the table caused it to sag, creating problems underneath. The laminex still adhered to the foam core but it had moved, just enough to cause the sag.
I've no idea what sort of glue is used on the paper back, so wouldn't trust using it.
