I'm in the middle of building a board and have a question about how to install mastrail. The core is XPS foam. I have a 10 inch vented rail from Chinook. I made a block of H80 divinycell foam about 38mm x 57mm x 350mm that I plan to route a pocket for the rail. The deck will be 3mm divinycell with fiber glass on top and bottom of the 3mm divinycell. My question is the glass schedule in the area around the mast rail; how many layers of glass and where exactly to put them in this area? New member so no pics 
I would put a layer of glass between the board and foam block and a layer between the mast track and the foam block. I think you may need to thicken the epoxy so it doesn't disappear into the foam. Slow hardener as well.
I put the boxes and plugs in after the divinycell , before the top layers of glass. Fill the box with stuffed in EPS and sand flat. I build my deck very solid because I'm heavy. Two layers of 4 oz all over, one layer 4 oz from in front of track all the way back , one layer 4 oz from back of track all the way back and then a couple small patches over the boxes , plugs and under pads.So that's 5 layers of 4 oz over the box. It's probably way overkill , but I've never had a box or plug failure. Start with the smaller patches then the half length then the full layers. Makes for a smoother finish. Proper board builders will give you a better idea for a normal construction.
Please post pics of the build.
You say xps foam for core, so a denser, stiffer, foam than usual core. Is it for waves, jumps or slalom?
Route xps foam tight, no space between divinycell block and core is better. Set divinycell in xps with at least 6oz glass and epoxy microfiber reinforced mix. Add fiber patch over this place when vacuum bag sandwich. For me it's where carbon is better: a deck patch from in front of mast track up to back.
Then route tight and set mast track with fiber, that lap on sandwich foam.
^^ agreed
block in first
then sandwich layer goes over with a carbon patch
I put track in that before top laminate as vac bagging makes it easy but a wet lam can be hard to avoid resin running in
Select to expand quotelemat said..
You say xps foam for core, so a denser, stiffer, foam than usual core. Is it for waves, jumps or slalom?
Route xps foam tight, no space between divinycell block and core is better. Set divinycell in xps with at least 6oz glass and epoxy microfiber reinforced mix. Add fiber patch over this place when vacuum bag sandwich. For me it's where carbon is better: a deck patch from in front of mast track up to back.
Then route tight and set mast track with fiber, that lap on sandwich foam.
I sail on inland lakes so relatively flat water. I used xps just because it was available locally and shipping a one piece eps blank was cost prohibitive.
Select to expand quotegraygeezer said..lemat said..
You say xps foam for core, so a denser, stiffer, foam than usual core. Is it for waves, jumps or slalom?
Route xps foam tight, no space between divinycell block and core is better. Set divinycell in xps with at least 6oz glass and epoxy microfiber reinforced mix. Add fiber patch over this place when vacuum bag sandwich. For me it's where carbon is better: a deck patch from in front of mast track up to back.
Then route tight and set mast track with fiber, that lap on sandwich foam.
I sail on inland lakes so relatively flat water. I used xps just because it was available locally and shipping a one piece eps blank was cost prohibitive.
Xps is heavier than light eps used with sandwich but it's overall stronger so you"ll have to fight against weight and you'll probably use more material than needed. When it's dented skin delam easily from xps but with divinycell skin it's hard to ding and strong.
^^^ yup
I would even think very hard about only divinycell deck, just do bottom with 2x 4oz to save weight
Select to expand quoteMark _australia said..
^^^ yup
I would even think very hard about only divinycell deck, just do bottom with 2x 4oz to save weight
This is a bit confusing. Are you advocating for no divinycell on the bottom?
^^^
yes as say for 100L the core is already 1.5 to 2kg heavier in XPS
Back before no sandwich boards, glass over 35kg ish PU was ok
So for a flat water board which won't be jumped and he has to use XPS core, I would think about just glass over the bottom.
but given the XPS offgassing issue, maybe not in hot places.
prob an acceptable way to have stiff board and heel dent resistance and as the bottom is pretty much just in tension just glass could be ok
I think so too Mark. Denser foam with lam bottom and deck sandwich is an acceptable, easier to do right build tech for a garage builder. I would not go with xps, have some problems here and there with this foam, but it can work. I like to add something to stiffen the board after hotwire blank, like a stringer or a composite rib, i find it's help me when (hand) shaping and glassing to keep rocker and foil right.
A local foil board builder is using XPS and intentionally not sealing the glass to allow offgasing. He also runs a spiked roller over it and leaves a rough sanded finish.
Then again foil boards don't need to be smooth.
^^ aware of that... not a fan
If only as XPS is such a bloody pain to shape, it tears.
He's saying it's a lot more durable and of course way faster to produce them like that. Pretty sure he doesn't bother with much carbon but does use some other fibers on the rails for impact resistance.
I've used XPS for models and it's definitely a pain to sand. Hot wires nicely and is very common for building here.
I have 2 layers of 6oz glass lining the cavity for the divinycel block and the block fitted to the cavity
Now on the the next question. Note the blue tape on the edge of the board, it's there to accentuate the rail profile. I'm looking for any advice on the shape before I start laminating.
Select to expand quoteHydrosurf said..
Have you seen the tool you can use to copy the rail shape? Is it a slalom board?
I have not seen a copying tool, it is to duplicate another board or just make sure I have the same shape on both sides?
It's meant to be my light wind board. I currently have beginner board that's wide and planes easy but weighs about 16kg. Some of the launch sites have a long walk to the water so I'm shooting to be in that 11-12 kg range. I'd like to be relatively fast for it's size but I'd probably still categorize myself as more freeride. It has a few more foot strap position options as I'm still progressing.
Select to expand quoteHydrosurf said..
Oh, yes I'm familiar with that tool. I have a similar one with steel pins and also one with plastic pins. Even the plastic one will mark the foam so I've only done a few spot checks for symmetry using that tool.
My tips only to prick it all very well for the gas inside to prevent delam
you cannot put too many little holes in it really
then get it warm for couple days
then laminate on a falling temp with the fastest resin you can get away with
Select to expand quoteMark _australia said..
My tips only to prick it all very well for the gas inside to prevent delam
you cannot put too many little holes in it really
then get it warm for couple days
then laminate on a falling temp with the fastest resin you can get away with
When i use xps now, mostly for light stringer (2 layers of 35kg/m3 xps with fiberglass between), i prep it like you, sand coarse, small pinholes every where then couple hours in oven to "open" cells at surface. Before lam i squegge a thin layer of resin and lam when it's set and tacky.
All full xps boards i see ( fill blank) still delam at dings. Punching holes in lam like XTR work to stop growing delam but i don't like and don't know how to do it right.
Now in Europe there are brands that make kite and foil boards with a denser, stiffer xps, mostly with carbon over. Less delam but when it start, where foam is crushed, it's a nightmare.
Thanks for the advice.
I've made at least a half dozen test panels 300mm x 300mm to work out the glass schedule and practice handling the materials and vacuum bagging and all that. They all laminate up just fine, no signs of delamination. The panel that seems to be the best compromise of weight and strength and ding resistance is; XPS, 4oz cloth, 3mm divinycell, 6 oz cloth. So that's probably what I'll go with for most of the board with additional layers around the stress points as needed. How can you even tell there's delamination in the XPS in a panel like that?
Pvc sandwich skin are stiff so less risk of delam. Delam from xps come from off gas of cell crush under impact dent. To test delam give a good impact on skin with an hammer, cut through it and look if it's still stuck to xps.
Like a good board build thread, great work greygeezer 
Interested in the xps foam, never having to worry about water getting in your board.
I saw on the sup foil forum a guy building his boards in Northern California. When asked about gassing I think his reply was 'pinholes are your friend '.
I know someone doing foil boards in XPS who really doesn't bother to fill the weave. No idea if they'll last forever but foil stuff is changing rapidly anyway.
PVC is now laminated top and bottom. Rather than bed it in the epoxy of the first layer of glass I bonded it to the first layer of glass using urethane adhesive. The foaming of the urethane fills under the areas that are not perfectly pressed to the fiberglass and has fill at least 3/4 of the gaps in the top.
Next will be to fit the mast track, foot strap inserts and fin box. When it come to final layer of glass what do you do with the fin box and mast track holes? Just glass over them or fill them with something? I plan to vacuum bag and I'm concerned about the bag collapsing into the holes.
