Well after the interest and feedback from people down the beach and pm's about my last 10 month board build thread www.seabreeze.com.au/forums/Windsurfing/Wave-sailing/Started-shaping-my-new-waveboard/ I'm starting up a new thread as I'm always tinkering with wave boards or fins or fin boxes or repairs etc.
Before I start with my stuff I really liked the board making vids that OES put up, if you didn't see that thread here's the link. www.seabreeze.com.au/forums/Windsurfing/General/Custom-Board-build-day-by-day/
OK well a couple of years ago Steve Stratfold who runs Steve's Surf Shed ( ph 0421 477 001 Unit 15/ 30 Peel Road O'Connor )
m.facebook.com/StevesSurfShed/photos/p.416519398402917/416519398402917/?type=1&source=46
Kindly gave me a couple of delaminated boards, Steve does great repairs and stocks Patrik boards and I think loft sails, please feel free to correct me or add other brands he sells.
Any way I cut the bottom of both boards of and have let them dry out in my shed the last couple of years.
My plan for my next project is to replace the polystyrene (eps) reshape a completely new bottom re glass it and use it for my high wind winter Hack.
This is great, I've got 3 boards with delamed bottoms, many say they are junk but I have never tossed them, even though they've all been replaced.
I've heard of so many ways to repair them but haven't taken the time to do what I know is a big job. So I will be paying attention to this.
I'll share one of the more interesting ways that I've heard of.
Cut the bottom off just like you did, make sure it's all dry, like you have, and here comes the interesting part.
Paint both surfaces of the split foam, making sure all loose chunks are gone first, with white Will Hold glue, the cheap stuff you can get anywhere, looks like cream. You can buy a gallon jug for around $10.
Then sandbag the bottom back onto the board, the more weight the better.
Supposedly that glue works really well with all types of foam, and you get your original bottom shape back with the minimal amount of effort.
Then patch/glass the seam using normal techniques feathering out the patch for strength.
It's the same glue they use to glue blank halves back together with an added stringer down the middle. So supposedly strength shouldn't be an issue.
Anyway it would be a cheap experiment.
I hope this thread will be of some use to you mastbender. Yes another way is to cut the bottom of as I've done and just paint a light coat of epoxy on then vac bag and glass around the cut. If the vac is too high you get a bit more concave so vac pressure is very important. Using the PVC glue you mentioned is great if the EPs remains 100% dry but with a delamed board that has dried out there is usually some dried salt that attracts any moisture like a magnet which then softens the PVC glue. You can get a special solvent based glue like a contact adhesive specifically for EPS but it needs to have an air flow for the solvents in it to evaporate, I learned this when using it with blue extruded Styrofoam I glued two bits together to get the right thickness the board delamed where it was glued together it was still tacky and not dry months later. Another way is to drill a series of lots of holes, then inject resin into all the holes, taped up all the holes keep rotating the board to spread the resin inside for 40 mins or until it starts to gel then vac bag, I've done this for a friend and the board lasted another 3 years until he got rid of it for a new one.
I'll be doing this board a bit different as I'll be shaping a completely new bottom shape, then use new glass and PVC instead of the bit I cut out.
I'm also doing this on the cheap by using offcuts and scraps that I have lying around my shed.
Well actually I'm sitting in front of the computer writing this. 
The most unique I've seen is Mal Falconers, he sewed the bottom back on (with I think aramid thread). I guess he injected some resin first, and soaked the thread in resin as he sowed. He drilled holes all the way through the board along the centre line and ground out a bit of a groove for the thread. I saw this when I was at Sandy point in 2010, as far as I know he's still using it.
I've done the resin, vac bag job, but there was so much damage to the internal foam, the bottom ended up with a lot of hollows, I had a fair bit of bogging to do to get it reasonable. But the board's still going after approx 5 years.
The best results I've had is what Mike's proposing now, replace the damaged foam and create a brand new bottom. The hard thing here is getting a dead flat surface on the old foam, so you get a good bond with the new foam, with no voids or a thick layer of resin. I'd left the bottom intact around the fin box where it seemed the box had held the board together, and forward of the start of the nose rocker, where that had also held the bottom down. As I wanted to recreate the original bottom as close as possible I also left the rails intact, so I was working in a well.
If you're making a completely different bottom, probably easier to cut the whole bottom of level.
Select to expand quoteR1DER said..
I have a plan to cut the whole bottom level.
I've heard of a guy who suspended a circular saw from the rafters, and used that to cut the bottom level, not a technique I'd recommend!
I just remembered how I did mine, I used rails and carriage to travel my router, (with an extended cutter) over the board. That worked quite well.
Select to expand quoteR1DER said..
Great minds think alike, I built a jig and ordered a wide router bit of eBay.
What type of bit are you using?
Yep, alike all right, mine was/is just about identical, unfortunately the rails on the board weren't straight so I had to provide timber rails alongside for the carriage to slide on.
Select to expand quoteBSN101 said...R1DER said..
Great minds think alike, I built a jig and ordered a wide router bit of eBay.
What type of bit are you using?
My router only takes bits with a 6 mm shank the widest one I could get is 25mm by 20mm deep.
I've seen sheets of eps 25mm thick at Clark rubber. So I'm going to cut to a depth of 24mm, epoxy glue in then sand flush with the rails.
Select to expand quoteR1DER said..BSN101 said...R1DER said..
Great minds think alike, I built a jig and ordered a wide router bit of eBay.
What type of bit are you using?
My router only takes bits with a 6 mm shank the widest one I could get is 25mm by 20mm deep.
I've seen sheets of eps 25mm thick at Clark rubber. So I'm going to cut to a depth of 24mm, epoxy glue in then sand flush with the rails.
I have a 38.1 leveling bit that would halve your time. But it is the thick shank. I got it from Carba-tec Perth. Must be hell messy
Select to expand quoteBSN101 said..
>>>>
Must be hell messy
Not as messy as carving out a whole board with an electric planner!
Its like white Xmas.
What's with the nuclear bomb resistant paint on these boards, don't really want to have to sand it of so I tried test spot with acetone hmm didn't dissolve it. Tried all purpose paint thinner ( I reckon this stuff is really toxic gives me a hell headache) no luck. Tried heat gun and bubbled up glass underneath, gotta repair a small section of damaged glass now! Kevlar carbon to be precise. Fnck I hate working with Kevlar when it Fuzzes up so easily from sanding.
I've bought some paint stripper from bunnings has taken two Applications to semi dissolve the paint. I might have to hand sand carefully so I don't sand into the Kevlar.
^^^ Like I said, the paint only falls off in areas you don't want it to, when repairing. Then a half arsed wipe with W+G remover takes the paint off... 
If the paint it that good, I reckon a light sand to almost touch the laminate then when all done just 2K clear the whole thing. Sh!t paint jobs are trendy :)
I do like your process so far, very interesting with the routering flat then adding new EPS sheet. Lateral thinking :)
Thanks Mark.
The new foam is 25mm thick, I've routed down 23mm and I will fill those couple of deeper spots with a light weight bog mix of qcell eps bubbles and resin.
I've decided to take out those two front boxes, one was leaking and I prefer US box system rather than the mini Tuttle, but still not sure if I should just leave it as a twin or add the extra front boxes.
I've made a template by rubbing pencil on the brown paper at the edges of the hole that I can then cut out and lay over the new foam to cut it to an exact size. I'll have to do some joins in the eps as the block isn't long enough.
Select to expand quotedecrepit said..
Well actually I'm sitting in front of the computer writing this.
The most unique I've seen is Mal Falconers, he sewed the bottom back on (with I think aramid thread). I guess he injected some resin first, and soaked the thread in resin as he sowed. He drilled holes all the way through the board along the centre line and ground out a bit of a groove for the thread. I saw this when I was at Sandy point in 2010, as far as I know he's still using it.
That was my old board, squashed flat while flying back to Cairns from Perth, even the rails were cracked. I was going to bin it but Mal wanted it, just goes to show what you can do if you're keen, he sails GPS and got himself a PB with it, how good's that 
what board is it? it looks like horrid Styrofoam? or someone really really really miss treated this board.
A really usefull glue is the one part polyurethane, used to be called vice, now it's sika tech grip. You can get it from bunnings. It is moisture cured and once cured nothing I know of dissolves it. It foams slightly when it cures so fills gaps like nothing else. If you mix water with it it goes creamy then foams up like expanda foam. It glues eps great as it expands Into the gaps. You can spread it out real thin and because it expands still get a strong joint.
Select to expand quoteP.C_simpson said..
what board is it? it looks like horrid Styrofoam? or someone really really really miss treated this board.
Every delamned board I've seen looks very similar
Select to expand quotePiv said..
A really usefull glue is the one part polyurethane, used to be called vice, now it's sika tech grip. You can get it from bunnings. It is moisture cured and once cured nothing I know of dissolves it. It foams slightly when it cures so fills gaps like nothing else. If you mix water with it it goes creamy then foams up like expanda foam. It glues eps great as it expands Into the gaps. You can spread it out real thin and because it expands still get a strong joint.
x2 good stuff. www.seabreeze.com.au/forums/Kitesurfing/General/woody-build/#1096537
Select to expand quoteP.C_simpson said...
what board is it? it looks like horrid Styrofoam? or someone really really really miss treated this board.
Its an F2 PC but I've opened up Starboard's, Quatros, simmers and they call look pretty much the same after a delam. The glass weave was showing thru from when it had got very hot and the epoxy starts to go soft. Probably been left in a car on a 40c plus day with the vent plug done up.
Select to expand quotePiv said...
A really usefull glue is the one part polyurethane, used to be called vice, now it's sika tech grip. You can get it from bunnings. It is moisture cured and once cured nothing I know of dissolves it. It foams slightly when it cures so fills gaps like nothing else. If you mix water with it it goes creamy then foams up like expanda foam. It glues eps great as it expands Into the gaps. You can spread it out real thin and because it expands still get a strong joint.
Thanks I'll get some and do some experiments with it, if it goes well I will try it on my next project. Going to use what I know with this one epoxy and qcell.
Can see where u hit that kevlar - fun fun fun
Intersting this is the third F2 of that model I have seen badly delaminated in the last month or so. Seems they were a bit dodgy. Then some RRD of same age had repeated bottom delam also. Cobra grrrrr 
Select to expand quoteMark _australia said...
Can see where u hit that kevlar
But wait there's more!! A lot more !!!( I fuzed up)
Excess protruding foam sanded flush with the rails.
Deciding what rockerline to use^^^
The origional bottom was double concaves within a single then changing into a vee in the tail. I'm going to shape just a single concave and also change the position where it flattens out and goes into a vee a bit further back in the tail, I also might add a couple of mm to the rail rocker between the mast and front footstraps. Well that's the plan.
I notice you write a lot of stuff on the rocker gauge to confuse any copycats
tick cross hole
vee runs longitudinally arrgghhhh
Just Asemic writings of a crazy mad man. You do know human civilization was here billions of years ago!!!!!! OOPART
I'm going to regrip a friends board so mine will go on hold for a bit I'll take pics of the process. I have rubbed back the old grip with wet and dry sand paper detergent and some water. Next weekend if the weather is good I'll do the regrip.
