This is an explanation of why low density EPS should be vented... 30 years of trial and error...
A properly vented low density EPS core can easily tolerate 100c with no damage... Way higher temperatures than any other core material before damage or heat distortion occurs..
I had one board back in Oz, it lived in my car for 7 years all year round, a dark blue Hiace van, stayed in pristine condition..
Don't forget, steam at 100c is used to expand EPS, so it's obvious it can tolerate those temperatures...
Another different issue I have seen, even with a functioning vent, boards left in a car with direct sunlight on them ( hatch backs being the worst offender ) can get so hot the core melts, this is not a pressure delam but rather a full core melt down leaving a hollow void, dark colors making it worse, this tells me the temperature must be reaching 110c or more at the surface of the board...
In the early days before I realized EPS needed to be vented, I noticed that the boards that blew up on hot summer days were always the ones we built in the depth of the Australian winter...
So I devoted a board to science ( one of many), I noted the temperature the board was glassed and sealed at, 31c, then placed it in my van with a thermometer on a hot day and kept regularly checking, it blew up at 67c...
So it became clear that the temperature the board was glassed and sealed at, determined what temperature it could tolerate before it failed and delaminated from heat pressure build up, about 35c difference...
Still didn't make the connection with vents, instead I built an oven and heated the boards to between 60 and 70c prior to lamination, concluding the boards could now tolerate at least 95c before heat failure...
2 major flaws with this theory... The boards were now almost permanently under vacuum or negative pressure at ambient temperatures, so if you damaged your board in the water, it sucked water like a syringe...
Issue number 2, One customer Jason Weeks will support this, he had an early one done this way, went 4 years in his car over the summer, then mysteriously it blew up, summer number 5, He damaged his board in October, fixed and resealed his board at a lower temperature, lowering the temperature now needed to do damage...
By that stage it had already become clear that vents were the ultimate solution...
For the first 10 years I ran manual vents, undo when not in use, tighten before you hit the water..
These still had issues, you either forgot to undo it and it still blew up in your car, or forgot to do it up and got water in your board...
Even tho each person who purchased a board had the vent explained to them, it was always difficult to make them accountable, plus now other retailers were also selling my boards and vents went unexplained...
So in 2005 I decided to swap to a self breathing Gortex membrane, set it and forget it..
This had 3 major advantages..
1, it kept your board tight and in great condition, it was always equalized, unvented and a board starts to fatigue and break down, gets squishy and worn out even if your not using it, coz daily, it's expanding and contracting, wearing it out..
2, if you did damage it in the water, being equalized, it wouldn't suck like a syringe under vacuum but rather just soak water,, making repairs way easier..
3, I created a connection I could screw into the vent housing, so if a board did get water in through a ding, I could simply blow in lightly pressured air and blow the water right back out the hole it came in, a few hours of flowing air and the core dried out completely...
Using Gortex vents, we still had the occasional delam due to a faulty installation, but covered those under warranty anyway..
These days we have a great new design, plus every vent is seal and pressure tested before leaving the factory...
if you buy a board that has an EPS core with less than 1.8 lb or 28kg M3 density, if it's not vented, your buying a lemon, not only will you have to always worry about heat, getting on planes is another major concern, I see just as many unvented boards blow up on planes as I do from leaving them in extreme heat.
There is one other scenario it's possible to go unvented, but it's still going to be a lemon, another subject...
Regards
Bert
Keep the info coming Bert ! It is so good of you to share your knowledge the technology has changed big time whether its a boat surfboard or ect ! You is the man ! Thanks for sharing
?? mind has been blown.....
Question, have you ever ever ever put a one way valve and pumped into a board an inert gas? Argon or nitrogen?
helium make it lighter ?
A gas with cooling properties?
Or for the mega mad man perhaps filled with butane and a clicker to operate f1 jet powers with a nozzle at the back.
But in all seriousness has it been done?
I always wondered when making a blank of it could be impregnated with helium or the like
Charle's law... all gases expand and contract with temperature change...
I can't remember the other law, Boyle maybe? Figured that it takes 273 degrees c to double the volume of a gas, or gas expands 1/273rd of it volume for every 1 degree rise in temperature.. so regardless of what gas you use, no vent, will still suffer the same fate..
Helium's biggest issue is, the molecule is so small, it migrates or diffuses between other atoms.. that's why a Helium filled balloon shrinks over a few days, and Helium filled containers need topping up regularly, as the Helium can still escape through the metal.. Flamable gases? Under water not so sure, Nitro Methane maybe, if you can get a spark to it..
probably best held in a self contained system installed in the board, like the old Nitro booster..
Yes I've had 2 eps unvented surfboards both have been lemons.
Consequently gone back to pu.
Never undo the vents on my windsurf boards and never had a problem had one since 2012 ,i guess the stronger laminates prevent explosion.
Foghorn, with a vent , even a manual one, at least you have some control.. When I did manual ones, I advised my customers with 2 options...
1, put it in your car vent open, get it as hot as its probably ever going to get, then do the vent up.. theoretically you wouldnt need to touch it again, until you damage it...
2, just do up and undo with each use..
Originally i used to do option 1 for the first few years of using vents... cook my board close to 100c then do the vent up.. one day during winter , board in car as usual , below zero minimum, i come out to my car in the morning and see my board has collapsed and shrunk, bottom and deck all sucked in..
I knew exactly what happened, opened my vent and for about 5 seconds , it made a noise like cracking a can of Coke, as the air hissed and rushed back into my board, luckily, the board popped back into position, that was the same board I mentioned above that lived in my car for 7 years..
Buster Fin, mate , if you have an unvented EPS board , then I cant make promises, young kid over here had one, i see the board in full sun a lot, tied off in the back of a pick up, so it could tolerate some heat, goes to Bali, board blows up on plane..
What i can say tho.. Unvented Brand new boards are less likely to pop than a used one..
as i mentioned in my original post , over time , daily you have expansion and contraction , this loosens up and weakens the board in general, effects the bonding of the beads in the foam... the one i mentioned above was barely 1 year old..
Interesting stuff. Thanks.
What about big boards like 14 ft SUPs. I have one that has a manual vent. The shop I bought it from said only undo it in a car ( who gets a 14 ft board in there car) or if you are not using it for a long time. Even in its bag it gets pretty hot. Thinking about installing a gore vent.
I have made some hollow wood sups and thought about filling them with some sort of gas. As you said not worth it. You can see the gore vent bubbling when you are paddling. Maybe fill hollow boards with some sort of light foam!!
The bigger the board the more vigilant you should be..
as I mentioned above, if you tighten the vent when its really hot, its under more vacuum as it cools, so a potential ding can suck more water...
the ideal scenario, if you will tighten and untighten with each use, I had one customer who kept a washer on his legrope, as my vents operated with a 20 cent piece, placed his board in the water and let it cool a bit before tightening the vent...
But just cooking it one time, and sealing the vent should be safe enough, as it will be under almost permanent vacuum, this also keeps them in relatively good condition as if you left the vent open so it can breathe instead of build up pressure...
Ctngoodvibes.. We also build plenty of unvented EPS boards.. but the density is 2lb , 32kg M3 or more... still get the occasional heat blister when leaving black boards in the sun, but those conditions will damage any core...
Most EPS boards built with the shape and glass method, like a P/U but different materials , will run a 2lb core, therefore don't need a vent.
anything with sandwich construction.. wood or high density foam, needs to be built with lighter cores.. these are the offenders..
Ahh yes makes sense Bert. Have been very surprised how strong the annesley eps has been. It has no stringer apart from a bit of carbon but has taken a beating anD survived. Originally thought it would be prone to snapping
Forgot to mention I told a mate about this thread in the surf this morning. Warning him his new FW spitfire might be best left home on his upcoming trip. He said yeah probably & then told me how he'd left a board in his car at the airport coz air asia were trying to rip him off. It had a few pressure dings before he left but was looking better when he got back lol
I've taken a few sandwich construction boards on planes without issue but they're low volume.
Just had a look at your website Bert, a 6'1 SX01 is looking real sexy to me right now 
MickPC I'm pretty sure the Spitfires ran a 1.5 lb core, they were the ones with timber on one side?
0.5 to 1.8 lb are the densities that will have issues, obviously it's less of a risk as you get closer to 1.8...
I mentioned earlier another way it's possible to avoid problems and the need for a vent...
Resin impregnating..
Most people who work with EPS know that if you laminate an unsealed board it drinks resin.. So much, that a handlam on light EPS. can literally drink kilos of resin, but if using a vacuum method that number can drop by 80%, so it's possible to completely infuse a short board core with 350 grams of resin, completely negating the need for a vent, coz there is no longer any free air space... This was the strategy of Surftech, but it's an extremely hard process to get consistent in production, individual laminators, how much vacuum pressure you run, any voids in the system that collect resin first, will determine if it's effective or not, I have one friend, has owned a Surftech for 15 years, multiple flights, always leaves it in his car, board is flawless, yet others popped their Surftechs first season... So it's a lucky dip.. Plus it totally kills the performance because of reduced flex...
Explanation time..
If you look at a cross section of light EPS it resembles filling a box with rubbery flexible ping pong balls, each bead is a sealed unit, like the ball, but then you have free air space between the balls..
One time I placed a cube of EPS in a glass jar, put the lid on then attached vacuum, The cube literally expanded by about 15%.. Each bead is a sealed unit containing pentane gas, so in a vacuum that bead will expand, like putting a balloon in a vacuum.. As the beads expand under vacuum, the free air space between the beads is reduced...
This spiked my curiosity..
So then I cut a 10 cm length off an old cardboard roll, the stuff your glass comes on, shaped a piece of 0.8 lb foam to fit in, lined the roll with a plastic bag, jammed the foam back in so it was a tight fit, dug a small well in the middle, mixed up some 200 minute low viscosity epoxy with black pigment added and kept pouring it in till it wouldn't take anymore..
Then I repeated the experiment, this time putting resin in the bottom of the bag, jamming the bag and foam into the cardboard roll, put a stack of shade cloth at the top and hooked up a vacuum, the resin sucked right through the foam with the excess collecting in the shade cloth..
Next day I cut both pieces of foam Down to an 8 x 8 x 8 cm cube to cut away excess build up on the outside, plus confirm my colored resin had gone right through everywhere, shaped a raw piece of foam the same size.. When I discounted the weight of the foam, the piece of foam impregnated with gravity was 5.5 times heavier..
Went the next step, calculated how much resin my vacuumed piece of foam was holding, then according to my calculations, I took a rocker bed, placed a waxed piece of laminex down, a dry piece of glass laid down, poured a 600ml puddle of the same low viscosity slow cure orange resin down the middle, placed a profiled rectangular blank down, put it in the bag and hooked up vacuum, within 40 minutes, the orange resin had drawn up through to the deck..
Next day peeled it up, cut an outline to confirm the resin had indeed saturated the entire volume of the board, it didn't get to the corners Completely , allowing for the fabric, and some resin that got past the outline, I figured 350 grams was enough to fill the entire core..
Starting again, I now made a board, and purposely used 350 grams more resin during the 2 vacuum stages, knowing my entire core was saturated...
The board was a ****ing dog..
it was stiff as ****, no flex whatsoever, no flex, no spring back...
What I had done, figured out after the fact, the resin had formed a matrix right through the core, connecting the deck to the bottom, this eliminated shear movement all together, so rather than a marshmallow like core that allowed my outer skin to flex and morph around the outside, allowing the springy properties of the skin and rails to do there job,, the whole structure was locked together...
This is the main reason you can buy a vacuum bagged composite board and one is totally magic yet another of exactly the same shape is a dog, how much resin did the core absorb???
The same reason one guy gets a board and it blows up in his car yet another doesn't..
My original goal was, can I build a sandwich board without a vent?
My conclusion was I can, but it won't go good, in the end the extra weight was as if I had a waterlogged board repaired and even that still would have gone better because of flex..
So the magic is in an exact amount of meager resin to apply skins, use a vent..
no problems and consistent performance...
Hope that was clear...
Great stuff. Thanks for sharing.
Off course at a certain pressure the beads will stop expanding and crush. First time I vac bagged a board I just glassed it and chucked it in the bag. Turned the pump on. Looked great for about 2 hrs so I left it. Came back 30 min later and it was crushed. Now I have a gauge and valve. I guess different density foams this will happen at different pressures.
I am playing with an additive that foams epoxy for bonding the high density foam to the EPS. Used it on cork as well. Seems to work.
Bert yeah the older spitfires had the wood parabolic stringers on the rails you could see unless they were painted like the hellfire with blue rails I had a few years back. I had to check the FW website to get some construction info on his newy he picked up on special for $550.
Site says;
1 - Entropy Bio-Resin Throughout
2 - High density Aerospace Composite Deckskin
3 - Top & Bottom Deck Sandwich Cloth
4 - Parabolic Balsa & Paulownia Wood Rails
5 - 0.8 lb EPS CoreHELIUM - ECOBOARD Verified - LEVEL ONE
Board appears all white, but interestingly they're still using the same tech on the rails but covering with a white skin. So unless you've been informed somehow, via web, wordamouth or breaking them lol your not gonna know the woods still there.
Funny thing is my mates broken an Evo (creased) & a FST hellfire (fully snapped) this year prior to buying the spitfire. Evo's same tech as his new spitfire & length of 5'8. Surfing well for him, hope he got one of the good glass ones.
Roger that on the lower volume being more susceptible to issues/problems.
Appreciate the explanations m8...cheers 
