Question about Epoxy/XTR Construction

First of all, Hi all, this is an interesting forum and I thought I’d join.

Now let the incessant child- like question asking begin:

I was surprised to hear that boards built this way had to have vent holes poked into the laminate.

My questions to all the guys out there are:

  • What is the difference between the XTR type of core and the sheet foam construction (basically core cell/ divinicell type foam) that was/is used for kiteboards? Is that stuff eps as well? The boards are made with epoxy as well and have no vent holes, and I've never heard of a delam issue of this type. Is the difference the vacuum bagging? I doubt it. Maybe the size of the kiteboards makes for less total gas volume?
  • Is this the only Current method to solve the outgassing problem? Would a vent plug work or not? (I get it about closed cell foam and air not being able to travel around the board, so I suspect the answer's no)
  • Where is the Gas coming from, the foam, the epoxy, or the reaction between the two?
Thanks. Not a shaper, but a dabbler

As promise what little I know…

My understanding is that XTR is XPS - extruded polystyrene.

A number of players on here have experimented with it.

In some ways it has a lot in common with XPS. For example it’s a good idea to vent it to prevent delams, especially with lighter build schedules.

First question - don’t know. Perhaps the difference is in the thickness, so less air gets trapped in it? perhaps the skins are far thicker so it doesn’t really matter? The latter makes sense to me because kiteboards are designed to survive a lot more stress than a surfboard.

Second question - I imagine a vent plug would work fine with XPS in a surfboard.

Last question - it’s locked in the XPS when it forms. As the board warms up that air expands. As it cools down the air shrinks.

Like I said I don’t really know. But hopefully someone with more experience can pipe in now.

Hi Doug -

As a vacuum guy you can test it yourself. Just rig up a small vacuum bag, put some EXP in it and cut a window. Seal the edges of the window to the XPS and apply vacuum.

Smear some water color against the foam where it is exposed in the window.

Depending on how far the vacuum line is attached from the window and how big your chunk of test foam is, you should be able to tell immediately if the vacuum is communicating through the foam and if a single localized vent would work.

I did a similar test with various densities of EPS. It helped me understand what densities might benefit from a vent plug.

My hunch (I haven’t tested XPS yet) is that vacuum doesn’t communicate through the foam. If that is the case, a vent would only work in a very localized spot where the vent is installed leaving the rest of the board subject to delams.

I like the idea of just poking holes with a wire brush or roughing up the surface with coarse sandpaper.

From what I understand D-cell core cell etc. are made from PVC, and XTR is extruded polystyrene not expanded with steam or however they expand it EPS.

Polystyrene is very cheap and PVC foam is very expensive.

If you look at the cell structure of XTR it is made up of tiny little bubbles filled with gas, this is what I think would cause the outgassing when the blank heats up.

Regards

Daren

XTR vs PVC foam are two totally different animals. One is low density building wall insulation the other a structural foam core for making high strength to weight composite sandwich panels. PVC foam is typically much higher density than xps. XPS has tiny sealed closed cells that have gas in them…they can heat up, expand and cause problems. Resin doesnt stick to XPS that good. A single vent wont do any good at all with XPS…vents are for very low density EPS foam.

The archive is loaded with such info…

PVC foam like corecell/d-cell is a completely different animal more dense and more strong with no outgassing except when you burn or melt it and then the fumes are toxic…

It doesn’t outgas when it heats up but more when the cells get damaged and gas is released so you have to find ways to

release the gas through the skin, protect the core or insulate the surface from releasing it’s grip to the skin.

XTR’s method releases the gas through the glass

roughing the surface boundry makes the binding layer more dense and harder to lift up.

another concept is to seal the surface with a layer that has alot of excess space in it such as EPS so an 1/8"-1/4" skin of EPS or balsa would help disburse some of the out gassing by containing and spreading it through that layer before it reaches the external glass layer.

Also XPS has other structural issues other than gassing that also make them prone to snapping beyond a certain tension point so you have to deal with that at well. The thicker the core the more potential to snap earlier in a flex.

Designing the structure and or how to build out the layers is something important to consider as well.

But their ride is much closer to PU than EPS is because of the density

and they are 100% water resistant which is all you can ask from any core or rail material.

With all the foam options out there there’s not a lot of good reason to be doing them over PU or higher density molded EPS blanks. But if your making your own it may be a better possibility than the EPS across the aisle at the big box.

I’ve only seen one label other than Soloman that is doing anything in volume retail wise with the blue stuff and the XTR cores are much more refined than the typical blue stuff.

Every hotshot shortboard PUPE to XTR convert I’ve seen riding them really loves their’s till the spring dies, which seems to be in about a year… I think it has something to do with the holes but I’m not sure… I guess if the core keeps out gassing it’s going to lose some of it’s spring over time.

I have shaped a lot of XTR and know that everyone love the lite snappy feel. The pin holes are vents. I’ve seen XTR glassed like a poly without vents. The guys ride them to death. Epoxy Pro has it down to a science with there pin hole venting. it is a very hard foam to shape. watch pulling screen on the nose? It rolls off if you go against the grain… It’s so light you can glass with 5oz and still get a real light board. Just keep out of the sun when its not being surfed. Just to be safe.

XPS is a closed cell foam. That’s why it is waterproof. Each cell has gas in it. All is good until the cell is ruptured, and then a little heat will make the gas expand and cause a delam. Cells get ruptured by dings and dents. But a single vent won’t work like it does on EPS because the cells are closed and don’t connect to each other. Even the Salomon board which is hollow doesn’t help with this problem. The XTR holes work a little bit because they are open, but they would have to be everywhere to completely prevent delams.

There are better ways to deal with the outgassing on XPS, but mums the word.

I had an idea about solving the dent->delam problem.

And I might try this on my next board. My idea was to make a decksandwich, like the compsand but then only on the deck.

This will prevent the pressuredenting and so the delams too.

And because the deck is more under compression and bottom under tension, I think this is a very good construction with the benefit of a waterproof core!

has anyone an opinion about this?

So it sounds like one of the big differences between PVC sheet foam and XTR foam from a behavioral standpoint is that the cells don’t rupture on PVC foam, at least not in any large quantity.

I'm guessing the sheet foam still has gas trapped in it as well, I can't imagine they're blowing bubbles in a vacuum.

This makes me wonder about the above solution as well, because whatever your top layer is, it has to be absolutely crush proof. If the deck were to dent at all, I’d imagine that the delam would be between the inner sandwich layer and the core now. 1/8th inch divinycell can definitely heel dent eventually.

That sounds scary now that I think of it. You have a board that can release a gas pocket anywhere you dent it, and there’s no effective way to channel that gas somewhere else, it sounds like, so it just wants to bubble up straight through the skin. Sounds like the current microperf approach that I see on alot of the production boards is not so much about letting gas travel to a hole and vent there, but more about poking enough holes in the laminate that any dent that occurs is likely to occur near one of those holes. Wow. Is that the case?

Quote:

You have a board that can release a gas pocket anywhere you dent it, and there’s no effective way to channel that gas somewhere else, it sounds like, so it just wants to bubble up straight through the skin. Sounds like the current microperf approach that I see on alot of the production boards is not so much about letting gas travel to a hole and vent there, but more about poking enough holes in the laminate that any dent that occurs is likely to occur near one of those holes. Wow. Is that the case?

Sounds right to me. If the delam starts between vent holes, you are screwed, especially since the foam-resin bond is not so good to begin with.

When you coat the blank ,do as normal ,then coat with epoxy rubber mix ,then put on your cloth over the blank and finish. If it delams ,simply sringe epoxy into the delam spots . If your getting heel indents, when laying up use a carbon patch where the heels go .

Thanks for the thoughts guys. Some interesting stuff there I hadn’t thought of :smiley:

Hope the original poster appreciates the CPR performed on this thread :wink:

Cheers!

The current EPS has gotten so good … why? Marko, American Blanks, White Hot, they don’t leak. So why drill holes and worry about gassing and delamination and snapping and … come on guys.

I do, this answered alot for me.

I’m partial to epoxy from a sailing/windsurf/kite background, but I’m not sure about XTR being the way to go as a core at this point. At least not for longevity, IMO.

However, I don’t think I’d feel the need to beat anybody else up if they wanted to use it, or keep trying to come up with ways to make it hold together.

The scratching the surface with a wire brush thing sounds neat as far as getting a good initial bond, but that only takes care of the outer layer of spheres in terms of outgassing. Any crushing that goes on underneath that layer would still have the same issue.

Thanks for all the info.

if you’re layering 3/8"-1/4" thick balsa, bamboo, cedar or paulownia with glass under and multiples layers of glass over with 3/4" to 1" thick solid wood rails I don’t think you’ll or should get get too much pressure compression issues with the core.

The key with a good compsand is that the primary strength is in the shell and the solid rails and all the core should be doing is providing filler. If the thing was engineered properly in the first place like Eva said the core of a modern sandwhich surfboard would just be air(maybe aerogel instead) …

I think that’s why Bert’s been such a strong proponent of the super lightweight cores cause his focus is in making bullet proof prefab shells and tailoring the flex with shape which includes core/rail and skin thickness. And if built correctly what ever that process is, I don’t think the cores in bert’s designs ever feel any of the types of stresses that would normally dent or fracture a core.

The question is how can you flex a xps core without stressing it to either outgas or break. For me based on a little experience bending the stuff for rail bands, it seems that if you glue up thin sheets inorder to to create the needed core volume and still allow for some slippage between them with a flexible adhesive then the thin sheets will bend very easy without too much stress. Also if the core it small enough and concentrated along the center of the flex axis then it really won’t be bending all that much anyway which is what I think Surflight is doing by wrapping that thick polypropylene shell around the narrow xps core.

For home made boards where you could careless if your board breaks or bubbles up then why not play with it since its waterporoof. But I’m with GL in that there’s just too many great foam choices out there to be monkeying around with the stuff for any type of production work. That is unless you have real good process to prevent pissed off clients.

The guys I know who are buying the XTRs are not buying them to last forever they’re buying them for the ride and the fact that they’ll last a little longer than a PUPE. These guys seem more interested in board performance than how long a board lasts… If they did they would gravitate to a Surftech but they don’t like the ride of those boards. In fact one of my shortboard lineup budz initially made the jump to surftech and after a couple of months switched to a JS XTR and now a Lost SD2 XTR.

I’m old enough to know to listen to the guys with the most experience and with this compsand stuff from what I understand that’s Gary Young and if he tells us that he’s changed his compsand wood board technique to use XPS inplace of wood rails and he’s at a point where he doesn’t even have to glass them at this point, I’ve got to respect that. The stuff everyone’s pretty much showing and doing with wood compsands today he was doing back in the 70’s and that 's a long time to figure what works and what doesn’t…

Your solid corecel or a solid wood kite board is going to be strong.

But for pure strength there are other options like Nidacore, Foaming Aluminum. Nomex Honeycomb, Ceramics, Carbon and Basalt fabric all expensive options but a stronger end product than whats being used in the surfboard construction industry. Just depends on how much you want to spend and whether you can get the stuff. For a kiteboard project if you want super tough and long lasting then you can resin infuse nida-core over with balsa/paulownia with carbon or basalt cloth with this new nanoparticle-epoxy resin. Should be bullet proof…

I wonder how soon someone will figure out how to cast a blank mold out of foaming aluminum to use as a core.