Blank and glassing, best strenght to weight combo?

General Discussion
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I’ve been trying to bone up on EPS densities and according to info posted on a couple of websites, even a relatively consistent foam like EPS has a range of weight per type.

Types I, VIII, II, & IX (in that order?!) have MINIMUM weights of .90, 1.15, 1.35, and 1.80 lb/ft3 respectively. ACTUAL weights range from .90-1.14, 1.15-1.34, 1.35-1.79, 1.80-2.20 respectively. As suppliers to various industries, most manufacturers adhere to ASTM standards which are recognized globally so those numbers should be consistent.

http://www.dyplastproducts.com/dpEPS_physical_prop.htm

Although not specifically related to density, some companies list bead size in their EPS specs but not many. My test samples obtained from various sources reveal that same density EPS foams do have slight differences in bead structure. FWIW, SFoam (http://www.sfoam.com/) has the tightest bead formation of all 2 lb density EPS samples I’ve received so far. IMO, this might be a factor as far as how easy the EPS is to shape.

Rich Harbour’s point about there being varying densities from blank to blank or even within the same blank with Clark Foam are well taken. For general purposes though, it would seem that all the foams mentioned have a range of weights for given densities and could still be used for basic EPS vs PU comparison.

Greg’s weights compare closely to what I obtained when I weighed a sample of Clark Foam. If Clark adhered to ASTM standards, we’d really have something to go on.

I guess in reference to the thread title, the big question would be how does type IX EPS (roughly 2 lb cu/ft) compare to any Clark Foam (they’ll all be heavier per cu/ft) in a standardized pressure denting contest? Does a slurry/spackle coat add anything in weight or strength?

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To get the weights we weighed the blank pieces on a lab scale. Pretty accurate scales here at PCI, they go down to 1/10,000th of a gram. To get volume we tank test pieces of the blank by submerging them and finding the volume. Doing this in a tank eliminates the need to cut accurate little pieces. From there you calculate weight. Many peices of a blank must be tested so you can get an accurate average. Also testing more than one blank is nessasary as well. As I said above there are obvious accuracy issues concerning density gradient and differences between the different plugs but surprisingly the samples from different parts of the blanks didn’t vary more than 1/10th of a lb in density. We saw that in the lab for sure. So the numbers above are fairly accurate but they are still generalaties.

Now with EPS you can be very accurate with weights. Most all the 2# density we’ve used over the years runs between 1.85 and 2.2. Mostly it’s right at or very close to 2#. The 1# stuff is generally quite accurate if your getting virgin material. It’s easy to weigh the block and then figure the volume and calculate accurately. There’s also little density gradient and every blank out of a block is the same density. In our tests through the years 2# EPS is about equal in compression strength to a blue and about 15% lighter than an ultra.

So in regards to strength to weight, which is the title of this thread, as stated above by Rich a urethane blank glassed with 6 and double 6 will be around 15.5 to 16 lbs.

A 2# density EPS blank with a 6 and double 6 will weigh between 11.5 and 12. For EPS this is a pretty lightweight glass job but is considered standard for high performance. From there each layer of 6 oz. per side on a 9’0" is about 1.25 lbs. and a 4 oz. is .75. So to net the same weight board in epoxy/EPS you would be able to put an additional 6 and 4 on each side. Pretty bullit proof.

Using sandwich construction totally alters the whole structure making very light, strong boards possible.

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As for bead size in EPS, there are generally four sizes used for block foam which is what we hot wire out of. There’s A, B, C, and T. There’s also TT which is what they use in cups. A is the largest (and not generally used anymore) followed by B then C then T. I’ve only seen T used once and fusion between the beads was not good. Even with C fusion is sometimes an issue. We generally use either B or a middle grade called B-C. This generally fuses the best and packs into the press well. C does pack a bit tighter but often has fusion problems which can lead to broken boards.

On densities, 1# foam is quite flexible, takes a lot of glass, leaks pretty bad, has issues with heat, probably should be vented but rides BITCHIN.

1.5 leaks less, takes less glass, is more stable to heat and rides really good.

2# doesn’t leak much at all, takes just the “usual” amount of glass, rides nice, almost never delaminates, is good against denting and has virtually no heat related issues. This is pretty fool proof stuff.

I’ve riden plenty of all three and my personal preference for performance is 1#. But I’ve had boards of all three that I really liked and I’ve broken almost every one of my 1#ers and only one 2# board in 25 years. In fact we pretty much never made any 1#ers for anyone outside the factory. And no thin ones out of 1# ever.

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Couple things about S-glass. The 30% refers to elongation. With polyester resin you already have e-glass beating poly in elongation so S isn’t gonna help you to much because the resins already failing before the glass with E. It is better with epoxy but that will be mostly against dings. The main thing is that S isn’t significantly better at compression strength which is really what matters in boards. So S has never really found a home in surfboards. Perhaps in the future someone will think of a way to use the stuff but as of right now …

Now Carbon is GREAT for compression. Rule of thumb for carbon is that one layer of carbon equals two layers of glass. It’s nine times as stiff and two layers of glass are 7 times as stiff as one so … pretty close. The only things holding carbon back from having real impact in boards is color and price. And just when it seemed price was going to be reasonable Boeing goes and buys up everything available for the next two years. There’s still some around but it is still black.

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hi greg thanks for that info…follow up Q on eps…

regarding the bead size / fusion relationship…larger beads means stronger bead to bead contact due what: geometry, reduced void, pressure or ???

is a B bead about 2mm in diameter?

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just thought i would throw in a few weights …

the last time i had a shaped urethane longboard blank in the factory, i weighed it …

at the same time i had just made myself a new board , it was called mutha chunka , it was a barge …

anyway the shaped p/u longboard blank 9’-2" x 22 x 2 3/4 === 10.3 lb …

my finished longboard with set fins 9’-1"1/2 x 24 x 3 === 8.6 lb …

if both boards were the same size , that means im making finished longboards 3/4 of the weight of a shaped urethane blank …

i sold the board 3 years later with not one dent in the deck …

and at one national title in 2002 the surf was that small that the whole team rode it , they would wait at the shore, as one person finished with it in there heat , the next guy grabbed it …

2 different people made the finals in there respective divisions …

but i just remembered , theres no benifit in using epoxy …

so if you want strength to weight , your wasting your time with any clark blank…

rich , that was bait , just jokes …

but seriously , i dont want to get debating again …

but they are the numbers …

the board im riding at the moment is 10.3 , finished weight and i hate it , its the heaviest longboard ive had in 14 years , and after picking up gregs board recently , there was barely a lb the difference and his board was 5 years old …

so your secend best option still doesnt involve a clark blank …

s glass , its strong …

im going back to s glass …

as ive been examining boards that have been coming back for repair , all the boards i did 8 to 12 years back are still bullet proof …

yes you can see the weave slightly , thats why i know they were the s …

one thing tho …

with polyester way harder to sand , because of what bill mentioned , the chemical the glass is finished in , i always made sure i sanded s glass boards real green …

but with epoxy , there is no noticable difference in how hard it is to sand …

who knows ??

greg ?

hank would know …

you gota get him on the sway program greg …

regards

BERT

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Greg/ or others with knowledge - - another follow-up…

Carbon - according to another post above - seems to have great strengh but little ability to flex - it failed/shattered after a certain weight was applied. Compression strength = harder to ding(right?), which is great - but if flexing makes carbon fail is there a more flexible alternative that has the memory/snap to flex well.

Kevlar ?

I’ve been considering making a board of Epoxy, #1 EPS (all I can get my mits on easily), no stringer, with a full deck patch of Carbon or Kevlar, 2x6oz. Eglass bottom and rails - and a vent (This is probably a 6’6" fish style board).

The idea being that the #1 (and all the air that it contains) is just like the beans in a bag. They’ll move with the flex of the boards skin. I want the whole deck patch to act like a leaf spring. to take the loading and unloading of turns etc. and return to shape.

Mixing Carbon, or Kevlar, with regular glass I’m sure creates different strength & flex properties and maybe problems where they meet up - but my hope would be that a full deck patch would disperse the loads and allow some useful flex.

And another thought - Stringers - logically - would seem to do just the opposite - focusing the load and creating a specific point for failure. but wood had the best memory for flex.

Anyway - I’m wondering about Kevlar’s properties compared to Carbon for my leaf/spring board. And if mixing with regular 6oz will cause big problems.

Thanks,

Eric J

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I wouldn’t do Kevlar. It is almost impossible to cut with regular shears and when you do get it cut it leaves a raggedy edge. It’s also not the most aesthetic color- yellow / orange. Finally, I’m not sure but the board Dennis Choate made with Kevlar had to be painted with linear polyurethane finish (it was a silver thing of beauty), I think because UV rays will degrade the stuff rapidly. Of course, if you want to be able to hit your board with a sledge hammer and not have it ding, or shoot it with a gun for that matter, then kevlar’s your material of choice.

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It isn’t so much the geometry of the bead but larger beads just fuse easier. They do because they allow the steam to penetrate the block easier. The better the steam penetrates the more thoroughly the outsides of the beads melt, the more surface you’ll have sticking to one another. Also as the steam penetrates, the beads are cold and tend to cool the steam. The more surface area the beads have (smaller beads have more surface area in the block) the more they cool the steam so your block inside isn’t fused as well. A lot of this has been worked out in new technology and the new presses have the capability of making just about anything we want. Unfortunately our industry isn’t big enough at this time to get those company’s attention. If everyone were making boards with EPS then we would see some manufacturers coming up with surf specialized foams. They would be stronger than what we have now, fused in such a way that board breakage would be a thing of the past and even the lighter weights would be leak proof. There are even some co-polymer beads that would provide for much better flex charateristics and dent memory. And we alsready have the resins to make use of these advances.

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Hey Bill,

Lets do a real life experiment. I have a 5-6 year old 8’ gunny shaped composite with all s-glass . eps 1.5psf Foam…4oz s…3/32 balsa then a 6 oz s top and a 4 oz s bottom and all epoxy.

I will compare against that sweet board you just built last week.

Any strength test you choose…use as car ramp, the 2x4 slam test… trampoline test or whatever you decide.

compare weight, strength, design, finish, looks and ride also prior to stress test.

I was an s glass only guy for about 5 years straight. As far as epoxy and s glass goes, there is no hot coat but just a second filler coat. This board the outer layers were vacuumed bagged on then sanded.The finish comes out nice. the problem was using the rr epoxy during that time with a tendancy to gum up if not attentive with the power sanding.

Though I still use s glass in places under the wood in certain spots, the outer glassing is fine with the less expensive E glass. The gumming up issues is long gone now. rr epoxy and fgh epoxy brand are both fine for worry free sanding now.

E glass 4 oz 52/52 thread, Breaking Strength(BS) = 220 LBf/in

S Glass 4 oz 52/52 twill thread BS= 300 LBf/in

36% difference according to the scientist.

I like the real life test. My very old epoxy S glass board will not be broken with a 30% increase were your new polyester board failed.

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Both Bert and CMP are using sandwich construction and while I’m not nessasarilly a proponent of S in sandard wet lap laminates I do beleive in sandwich construction you do get advantages that are worth the investment. This is because so much of the structure of the board is built into the composite itself and not left up to the glass job alone. Changes many things and makes the advantages S does have stand out.

Having said that there are those using S in TX and are getting amazing results, Henry Fry, Bob Martin some others using 2# EPS and standard layups of triple 4 S bottoms and quad 4 S decks. Sounds like a lot of cloth, and it is, but the boards are still much lighter than the standard poly … and wayyyyy stronger. I know this also sounds expensive but they have an in at Hexcel right there in Houston and buy end rolls for less than 50 cents on the dollar. From what I’m told as many end rolls as they could ever use.

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Hey Greg -

Thanks very much for the EPS info!

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EricJ…

While KEVLAR has some great properties, there are also some problems associated with the material. One thing to keep in mind is that KEVLAR likes to attract moisture. Being hydroscopic on a surfboard isn’t always desirable. In addition to being hydroscopic, KEVLAR does not “wet-up” very well. The resin tends to encapsulate the fiber rather than saturate the strands, which would bond the matrix together. Kevlar works well in a prepreg and autoclave application, but the high pressures and elevated temperatures would turn you board into goooo.

Just something to consider…

Good luck!

Ken

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I’m not a fan of Kevlar either. Not in boards and not in its present application in boards. It’s just not a great wet lay-up material. Like Airframe said, it’s application is a bit beyond where surfboard building is today.