Pin holes and open foam wouldn’t be a very good idea.
Back to the original experiment. The foam block wasn’t sealed in any way. All it took to fill it with water was some pressure from a fingertip.
So you duck dive your board and grab the rails? Water gets in. You catch a wave and stand up? Water gets in.
EPS foam is pourous like a sponge. The holes are small, but they are there. As soon as enough force to overcome the surface tension of water is applied, it saturates.
As to coffee cups and why they work, I can only guess. Are they sprayed with a sealant? Is the surface heat treated to melt the skin? I don’t know. All I’m sure of is that even Superfused blanks absorb water.
I’ve seen practically new dinged eps core boards with a couple of pounds of water trapped inside…where it literally ran out on the ground when the hole was opened up. Vacuum pump needed to extract it but you never get all the moisture out. Never seen anything like that with PU
Without the pores – interconnected air spaces – I do not believe EPS (polystyrene) would bond as well with Epoxy, mechanical bonding.
I believe coffee cups, like the foam in egg cartons and that used for packaged raw meat, are XPS. XPS is non-porous and does not absorb moisture/water – closed cell.
Eva, the boardlady, showed us how you use vacuum to pull water out of an EPS board. She had it on her website for a long time. It takes time to get it out if you want to do it right.
If I come out of the water or get home from surfing and notice water bubbling out, I use my mouth and suck the water out just like you do when you’re trying to suck venom out of a snake bite. Keep at it until you stop sucking water. Mark the spot and then let the board sit a while to dry. Before you repair it, let it get warm enough to blow air out then do the fix where it will be cooling off to suck the resin into the hole.
It should be noted that with epoxy (used with both EPS and PU), dings tend to be dents rather than fractures which is an advantage. With a skin pennetrating ding I get out of the water with either PU or EPS. Just makes good sense.
EPS is beads that are pressed into various shapes, XPS is not beads and is directly extruded in a liquid state. Both are closed-cell foams. Since XPS has no air spaces, it has much lower water absorption than EPS. Coffee cups are indeed EPS and are formed against a hot-walled mold which fuses the beads together and forms a skin. Can also be done using high pressure (heat = pressure). “Styrofoam” is a Dow trade mark for XPS; the hard rough textured stuff you see in craftstores. Marko and other “superfused” blanks have a skin on them like the coffee cups and the beads don’t fly around so much when shaping.
Despite the various hypes on EPS improvements, keep in mind that you can’t really change the basic characteristics without changing the density. The degree of airspace within EPS foam is what decides the density and is typically determined by bead size. Normally the lighter the density the larger the beads, simply because larger spheres don’t pack as close as small ones and there’s more air. Higher densities can be smaller or mixed bead sizes since this will pack together the closest. There are specific pressures for forming EPS because if the beads are smashed together too tight, the density will be inconsistent. So at the lightest densities like 1 & 2 lb/cf which are almost 90% air + CO2 fill, there’s not a lot that can be done to alter characteristics like water absorption, heat expansion, and such without changing the density.
Yes, it’s all that other stuff as well. PU on the other hand is the foam of eternal righteousness, sent here by our benevolent creator for the good of all mankind.
EPS beads are created by heating initially small polystyrene beads, expanding the pentane gas within each bead. The small
EPS beads are expanded as much as 40-fold before cooling and curing. Temperatures for expansion and then cooling/curing are carefully controlled. Expanded beads that have been cured are then fused with heat when placed in molds.
As you say, there are many interconnecting air passages among the fused beads and the amount of air present determines foam density.
I understand the tests that Everysurfer is doing…I also understand what PeteC is saying…(you might want to re-read Pete’s stuff)…and I jumped on board the EPS band wagon when Clark foam closed…It is real simple. They sold us 1.5 pound foam but told us it was 2 pound. We learned on Swaylock’s to glass the boards with one layer of 6 on the bottom and two layers of six on the top. Most of my early boards did not dent ,crush or delam…But the foam got better and the glassing got lighter…bad deal…I’m guilty too… Quality EPS foam with a quality 6 ounce glass job will yeild a stronger better surfboard. Hands down…
But Light Blanks with light glass jobs seem to be what people want or are told to want…most people I deal with do not know what EPS foam is…
EPS has some very good attributes for performances , apart from the downsides . The obvious one is the weight , or , lack of it . Heating the surface of EPS with make it closed cell , like PU and XPS…Slurrying with a thickened epoxy will also close and seal the cells… . If you pour un-catilized, unthickened epoxy on the deck of a shaped EPS blank , it will eventually go right through the board and drip onto the floor underneath it , which is why it’s so hard to get the water out , once it gets in…my current worload is half EPS , half PU…they both have their place…just gotta work with them , and not cut any corners to save money…shortcuts cost you in the long run.
6 bottom double 6 top over 1.5lb EPS is what everyone who likes PU hates about EPS. Although the weight and durability is good, that much glass locks up the flex and leaves you with a chattery board.
I fully agree with stingray, for monolithique build need good quality dense eps with décent lam, at least 6+4/6 oz to be valid, but pirate agenda you are often right if board have a stiff wood stringer.
6 bottom double 6 top over 1.5lb EPS is what everyone who likes PU hates about EPS. Although the weight and durability is good, that much glass locks up the flex and leaves you with a chattery board.
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I disagree Pirate Agenda…
I spoke with a very well known shaper who does a lot with EPS and he convinced me that it is not the amount of “flex” that folks don’t like with EPS, it’s the rate of return. Basically, they will both flex roughly the same amount BUT, EPS returns from it’s flex faster than PU and that’s what makes it feel chattery…
His answer… Build the flex out of it in certain key areas.
His boards are well loved by the masses and some pros.
I’m wondering if the ride difference between the two is something else. Resonance.
Tap on an EPS blank, and a PU blank. They sound different. The EPS sounds crisper. They vibrate differently. Maybe that’s what the surfer thinks is chattery.
As for the ride, maybe I’m just not good enough a surfer to tell the difference between the two.
Shape, stringer, over-all weight, fins and their mounting of glassing or box, I can feel a difference. But PU or EPS are the same to me. Until they get a hole in them.
On a normal(i.e. glassed normally) eps board, I can’t really tell the difference either. When I talk to friends about it that aren’t aware, when I say the words,“epoxy” or “eps”, they immediately think of surftech or NSP type boards which I can tell the difference without question. Those boards with that type of construction definitely feel chattery.
On the other hand I have had two firewire boards that I really liked, and those were mass produced, but had a really good feel to them.
Benjamin Thompson here some years ago give us results of a real searching work about Surfboards flex where he explain how it´s a dynamic (vibration) problem. Résonance is a main part of this dynamic comportement. After my one search i can say that´s not a stiffness (static) problem, but more a dampening thing.
I agree with the idea of resonance. Which is why the shaper I mentioned above limits flex in certain areas of his boards.
EPS tends to “return” quicker than we expect it to or, at least, quicker than PU normally does. This quicker return doesn’t feel good under foot as it throws off the rythm…
Here’s what I posted on the Pro’s and PU thread:
What is usually attributed to weight is actually due to resonance.
I don’t buy the negative effects of a shortboard being blamed on .5-2% of overall weight change. That’s silly.
I spoke with a very well known shaper who does a lot with EPS and he convinced me that it is not the amount of “flex” that folks don’t like with EPS, it’s the rate of return. Basically, they will both flex roughly the same amount BUT, EPS returns from it’s flex faster than PU and that’s what makes it feel chattery…
His answer… Build the flex out of it in certain key areas.
His boards are well loved by the masses and some pros.
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Yes it agree it’s the liveliness of the foam that is the main cause the chatter. but people still want the flex. locking it up with lots of glass makes it feel worse. pro PU boards use as little glass as possible to allow them to flex. the key to getting EPS to work is figuring out how to settle down the vibration without locking up the flex. this can be done with certain materials or as you mentioned shaping techniques.