I’ve tried searching for this topic on so many sites but haven’t been able to find it. I want to make my own 9’ to 9’3" ish blank and would like it to be out of XPS foam. The biggest this foam comes is 8’ so I was wondering if anyone thinks its possible or smart to do this…
Adding about a foot of extra foam to the 8’ long board and gluing them together with a polyurethane glue? I was also thinking it might make it stronger if I could insert a small wooden beam into both ends of the 8’ board and the extra foot of foam to make it stronger?
Let me know if this is too crazy to try or if you have any advice, thanks!
If you aren’t using multiple thicknesses of foam and are unable to stagger them, I would cut like shown below (top view), and glue with epoxy or polyurethane.
3M 78 works fine for XPS. Could be a bit of a challenge for gluing foam strips. The trick for 3M 78 is allowing a 36-48 hour cure time for maximum bond strength. It sands better if shaped right away though.
Pretty sure Sharkcountry and Oneula use polyurethane glue for their XPS builds.
The biggest challenge with foam mosaics is sanding glue lines.
EPS and XPS are both made from “polystyrene.” FTR the only reason EPS bonds better with epoxy is because it’s porous. The adhesion problems with XPS and epoxy are because it’s 100% closed cell (not porous) – reason why XPS doesn’t absorb water when dinged. XPS adhesion problems are also related to using low density XPS (1.3 pcf).
However, I agree. Gluing up a few pieces of scrap XPS with polyurethane glue and 3M 78 is a good test/practice run.
Minimise the glue lines if you can. They do require extra attention at the end as they will all stand a little proud of the surrounding surface and you have to go around with some sandpaper and a small, hard block, and finish each of them back.
I prefer staggering the foam the way the way Stoneburner shows compared to the way RDM has it. Done it both ways, and it’s easier to glue straight lines versus the vee cut. I also have made many by cutting rocker strips to get more rocker than the foam I had would allow. A foaming polyurethane glue like Gorilla Glue works really good on XPS.
I’m backing off from XPS due to delaminations caused by heat. You can add pinholes on the board to help avoid heat delams. Last summer was pretty hot here in Hawaii and 2 of my XPS boards developed large delaminations. They were stored outside in a well ventilated shed.
XPS shapes easily compared to EPS. I make a lot of my boards stringerless and they’ve held up to the abuse.
Something that I noticed a few years ago, when I stripped and made a new board from an old XPS board I had… the glass peeled off very clean and very easily. This is probably why it delaminates so easily.
I like the way xps shapes and rides but they do require a higher level of care insofar as handling and transporting are concerned. You can’t let the board get any hotter than it takes to melt the wax on the deck. In cool climates that’s not a problem. But leaving the board exposed on the beach on a hot day or leaving it in your truck on a hot day is a no-go.
I wonder if that issue could be eliminated by perforating the foam in the fashion of a wallpaper perforator prior to glassing? A whole bunch of tiny holes to give the resin something to bind to…
I know that German guy who came up with the Hydroflex glassing technique does something along those lines. At Boardroom a couple years ago he had taken one of his boards and sliced it into quarter inch slices. You could not pull the glass off them.
Javier at XTR adds tiny holes after the lam to allow air to escape to help avoid delams. XTR had a really good white XPS foam. I don’t know if they still have that foam, but I liked it.
That board I showed was sanded with a block and 60 grit media. It is really course compared to a finished PU or EPS blank. The foam is blue Dow XPS.
I thought the hydroflex boards used EPS foam, but I don’t know for sure.
Javier at XTR adds tiny holes after the lam to allow air to escape to help avoid delams. XTR had a really good white XPS foam. I don’t know if they still have that foam, but I liked it.
That board I showed was sanded with a block and 60 grit media. It is really course compared to a finished PU or EPS blank. The foam is blue Dow XPS.
I thought the hydroflex boards used EPS foam, but I don’t know for sure.
I shape the XPS with a surform and 60 grit. I final sand to 100 grit. I then vacuum foam dust off surface. Then I use a modified TopFlite Woodpecker Tool (doubled the number of tynes). I perforate the shaped foam with the WP tool. I pre-seal with a thin layer of epoxy. Then sand to 150 grit. I laminate using epoxy with opaque white pigment (to reflect solar heat). I don’t use less than 1.55 pcf XPS. Saving my higher density XPS for when I have my new designs well dialed in.
The perforations the WP tool makes are linear. So I have started playing with the orientation of the slits relative to the long axis of the board.
Next board, I will pre-seal using epoxy with opaque white pigment and vac bag the pre-seal into the perforations. Tried 45 degree orientation last. Will try 90 degree next (should help minimize parallel surface movements of the glass skins). Will also laminate using epoxy with opaque white pigment.
Pretty sure I have it mostly dialed in now. But XPS does get soft in high heat.
I still have a few tweaks I can try to further imrove bonding/prevent heat delams (one would be using white EVA foam on the deck).
But the number one of advantage of XPS is it does not soak up water – 100% closed cell (does not breath).
Top tool in picture below has 8 rows of tynes (modified). Bottom tool only has 4 rows of tynes (stock).
When we started make airplane RC wings by vacuum bag fiber and resin we used xps. No problems. At that time i made surfboards with Clark foam and sometimes epd/epoxy. Tried xps surfboards but every times delams under foot even with punch holes foam. Bufo (hydroflex) were first pu foam with punch holes then went to xps punch holes then to eps… Salomon bleu were a thin layer of xps, surftech tufflight use some xps for sandwich foam when they move from pvc foam to wood. Each time i repair some i must take care to not Peel off too much skin…
Perforation number, size, shape, orientation, surface area (internal & board surface distribution). Large (relative) circular perforations have low surface area to volume ratios – you want high surface area to volume perforations.
Glassing schedule.
Load and impact dispersion (deck skins: EVA, Cork, etc).
Foam temp (internal gas volume) at time of glassing – core and surface layer – affecting post glassing expansion and contraction. XPS does not out gas (closed cell foam cannot). Which is more likely to cause delamination, expansion or contraction?
Hand oils on the surface of non-porous foam, from handling during shaping and glassing. Wear clean or new dish washing gloves.
Board color – white to reflect solar radiation.
Design and construction must consider these variables.
There are many generalized assumptions when discussing XPS for surfcraft. I am not trying to convince anybody to use XPS. Just offering input to those who do want to try it…
Except adhésion problem xps is best foam for boards for me. Xtr delam around holes even if their foam is better than standard one’s. Broke lib tech skin show easy delam even with multiple punch holes grip and stiff skin. On other hand many guys build their one ez rutan plane by laminate fiberglass on spider foam ( dense xps) and they flight with so…
As with any foam, XPS has its limitations. But all of the variables must be properly controlled first.
I had not seen LibTech products. They claim “impact resistant” and “dent inhibiting.”
I think the deck skin property needed is impact “absorbing,” possibly used over FG. I suspect cork would work well, probably better than EVA. Maybe EVA over cork. But the correct thickness and density of a PE or PP foam deck skin would likely work too.
My board building was always experimental and always for my personal use. I’m probably at about 70-80 boards made now. The foam I use/used and the processes were never done under the best practices, they were done with costs in mind. I have access to the best surfboard materials if I want to go that route, but the EPS and XPS foams I used were always extremely inexpensive, even free. You won’t get the best results when you work the way I do, so when they have issues, they may be due to improper construction methods. I know many failures are due to my bad decisions, or lack of thinking things out better. Failure is a big part of learning, so I don’t mind some of it. What really sucks is when you make a good board and really enjoy using it, then it delams bad.
It will take making more than few boards before you figure out all the nuances of board design, not even mentioning the glassing half which is way more work and where a lot of the costs are. When I started making boards again, I had a good job and a lot of “play” money, so the resin and the other parts of making boards didn’t matter. I’ve been retired and living on much less for 4 years now, so the costs matter now. I’ve made boards with PU, EPS, XPS, hollow wood, and wood veneered. I’ve made boards with a mix of EPS and XPS too.
If I were to rate the foams I use, I’d put EPS above XPS even though EPS will suck water like a sponge. Main reason is I live in a warm environment, the temps never get too cold, but it does get hot at times. I have way too many boards to keep them cooler than the air outside, and we’re seeing temps get higher every year. If you leave an XPS board in the sun it will blister. Other than the heat problem, I like XPS foam. The hollow boards are at the bottom of my list because the places I surf are far from shore and any failure of the hull would be a big problem.
