This post is sort of a cautionary tale and then leads into an experiment. If you’ve been around wakesurfing for any length of time you’ll recognize that many wakesurf boards are built from a core of EPS foam. EPS is short for Expanded PolyStyrene foam. Polystyrene is a plastic and it is found in everything from disposable coffee cups to the dashboard of your car. It’s a remarkably versital plastic and can be injection molded, extruded and just about all manner of processing.
Now for wakesurf boards, the most common method is block molding in which small beads of EPS are pre-expanded, then dumped into a mold and heated up again and also compressed. The beads get soft and melt together and the expansion from heating sort of forces the beads together. The key point there is that the beads aren’t glued together, they are melted together. Now EPS foam comes in several different densities. The most common for wakesurf board construction are 1 pound, 1.5 pound, 2 pound and 3 pound. But, there are all manner of other densities available.
Ok, so here is where the cautionary tale comes in. You may have seen wakesurf boards with one way vents in them. The Walker Project was one of the early adopters of this tech. Although they no longer use that with their newest construction. There was this thought that lower density EPS foam would expand at a higher rate than higher density EPS foams and so anything below 1.5 pound density needed a vent. There was never any factual information to back that up and it was sort of a rule of thumb and would be tossed around like a football.
There was a discussion on a wakesurf forum that is known for it’s spamming and misinformation. It started as a “look at my board” and spam the manufacturer. The board had a deck of black carbon fiber. Another manufacturer came in and said that needs a vent. Another shaper came in with the rule of thumb is 1 pound does, but nothing above that and finally the owner came in with his board was placed in an oven and so didn’t need a vent. No one questioned that.
So the oven toasting is referring to post-curing of the epoxy and has nothing to do with heat-treating the internal foam. Epoxy needs a post cure to reach it’s full cure and strength. We’ve discussed this in-depth in previous posts. Neither foam nor air can be heat-treated to prevent further expansion or to make it tougher. But also remember this, online forums are filled with all manner of misinformation.
So let’s go back to the whole concept of heat causing EPS to expand and that 1 pound needs venting whereas 1.5 and above doesn’t. That almost sounds reasonable doesn’t it? Certainly you’ve probably never seen a 3 pound density EPS foam board with a vent. Let’s get some factual information here.
There is a term when measuring or grading EPS foam that deals with this expansion. It’s referred to as the Coefficient of Thermal Expansion. It’s a fancy term for how much does the EPS foam expand with each degree increase in temperature. It just so happens that within the useful temperature range of EPS, that expansion is linear. So for each 1 degree increase there is a specific amount of expansion.
BUT, if all of the talking heads were correct then we would expect each separate density of EPS foam to have a unique Coefficient of Thermal Expansion. AND if the whole 1 pound needs venting and the others don’t we’d also expect the 1 pound density foam to have some crazy larger number compared to the other densities. AND if we believed any of that crap, we’d be wrong.
Welcome to misinformation age!!!
All EPS no matter what density, has the exact same Coefficient of Thermal Expansion. So no matter if it’s 1 pound or 3 pound density, it expands at the exact same rate. Here is a link to a common table of physical properties of EPS foam. It’s just the first one we found, so feel free to google the CofTE for EPS and you’ll find that same table again and again. Working up from the bottom, the 3 item is the Coefficient of Thermal Expansion.
Did you find it? The three columns correspond to 1 pound, 2 pound and 3 pound densities of EPS foam and each shows the same number:
Coefficient of Thermal Expansion in./(in.)(F) 0.000035
Huh! No matter what the density, it all expands at the same rate. Wait, wait, wait! 1 Pound needs to be vented! No it doesn’t, just more crap that gets tossed out there from folks that really are being negligent. If you don’t know, just say that. It’s fine to say: I don’t know that answer, but I’ll sure find out! Instead it comes out as: my ego’s so big don’t question me and you’re a poopyhead for even asking. Blech. Anyway, the reality is that ALL EPS foam would benefit from a vent, if the board is going to be subjected to an environment where heat and this thermal expansion is going to be an issue.
Anyway, all EPS does expand and all EPS expands at the exact same rate. That’s true because it’s all the same stuff. It’s Polystyrene, pentane gas and air. The plastic doesn’t really expand measurably with heat, but the two gases do. And we’ll repeat this, they can’t be heat-treated to prevent further expansion. So normally there is some truth to these wives-tales. If we see large 1 pound density SUPs they often have vents. So here is our thinking. ALL EPS can benefit from a vent, especially those being subjected to extreme heat or heat build up. It’s not strictly 1 pound EPS, but ALL EPS. We’d also think that folks that are working with higher density foams have their processes worked out, so have found that within a relative range, venting just isn’t really needed to prevent delamination or other failures. The folks that use 1 pound without vents, like Surftech and Inland Surfer have refined their processes so that the vents are needed.
If you are making $2,000 SUPs, a $20 vent is pretty safe way to avoid returns if folks are leaving their SUPs out in the sun all day long.
Really, we think that’s probably the long and short of it. Not that 1 pound needs venting and other densities don’t only that the processes for some have been worked out and the rest haven’t figured it out for 1 pound or the manufacturer says, $20 is cheap insurance!
So we decided to do a little test, let’s get some factual information here. So here is our test, we took a piece of really crappy 1 pound density EPS and laminated it on all exposed surfaces with some 4 oz Carbon Fiber. It’s nice and black and the core is really crappy low density foam, probably a little lighter than 1 pound, it feels like a nominal weight of 0.5 pound density.
We’ll post cure the project and then take it out and leave it in the sun. We are hoping for some 90 degrees days here in NorCal soon. We’ll leave it out all day and get some temperature readings. What we are wanting to test is whether it will delaminate and if so at what temperature.
We don’t question that it’s possible, only that 1 pound or 3 pound will both delam at the same point and also, it really requires that you mishandle the board. Don’t leave your black EPS board in the sun, unprotected all day.
So here is the lamination process. A chunk of EPS foam and some scrap Carbon Fiber cloth.
We wrapped it up like a Christmas Package and then wrapped that with clear plastic wrap to hold it all in place while the epoxy cured.
Imagine that’s a carbon wrapped EPS board! We’ve used plenty of Epoxy and then squeezed it nice an tight with the clear plastic wrap.
It’s currently RAINING in NorCal, so we won’t be testing the whole heat expansion concept today, but the weekend is projected as 90, so hopefully that will give us some useful information. We may not be able to replicate 110 in the shade conditions, but if we can get it to delam, we’ll know at what point that took place and if your environment is cooler than THAT, you should be golden.
Thanks so much for following along, we really appreciate it. Hopefully we’ll get out on teh water this weekend for some buoyancy testing!