From everything I’ve read it seems like the integrity of the board has everything to do with the bond between the foam and the fiberglass on the deck side right? The glass has to be thick to ward off heal dents and compressive strains,but as soon as that bond is eliminated, the glass fractures. So why hasn’t anyone figured out how to chemically bond polyester or epoxy to polyurethane or polystyrene? Seems like that bond line would improve the strength quite a bit and then you could cut down on the glass schedule.
Different chemicals. The best you can hope for is a good mechanical bond, which a good epoxy gives you. You’d have to laminate with a urethane resin on the urethane blanks. It’s been tried but I understand the urethane lacks the proper mechanical properties needed for a surfboard.
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Different chemicals. The best you can hope for is a good mechanical bond, which a good epoxy gives you. You’d have to laminate with a urethane resin on the urethane blanks. It’s been tried but I understand the urethane lacks the proper mechanical properties needed for a surfboard. Right- up to this point a mechanical bond is all we have been able to come up with. You’re right the chemicals are incompatible for forming a chemical bondline, and polystyrene has no chemical bonding potential as is. But say it were possible to chemically modify a thin layer of polystyrene (or polyurethane for that matter) at the surface to allow bonding directly to polyester or epoxy- would this be of interest on a structural basis? The reason I ask is becasue I’m a chemist and I know it can be done. I just wondered if it would be beneficial.
It seems that when I see glass that has been stripped/delamed off a board it takes a thin layer of foam with it, making me think the bond is ok. Even with a perfect bond, if you lightened your glassing you’d get some heavy heel pressure dings…mashed/broken up foam that is no longer structurally intact that can pull apart…spider cracks…leaks. Resin penetrating deeper into the foam would help here but then there goes the weight.
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Good point. I was thinking a good bond would be more likely to pull out small irregular sections of foam and more of it. Doesn’t the glass seem to come off just a little too easy. I stripped the glass off an old boards the other day and it just peeled right off. The only resistance came from the stiff glass. The bond hardly seemed to give any resistance and it got me thinking. As far as pressure dings go, don’t know if my arguement holds any water, but if there is a very strong bond between the foam and glass, wouldn’t the foam tend to rebound with the glass. And if both the glass and foam are sunken- atleast they are still more structurally sound, not delamed?? Not sure what would happen to the foam- once crushed is that section ruined for good or would the sring back have any effect? At any rate, it couldn’t be worse than a delam anyways. One last point- the leaking on EPS could be fixed with the chemically modified outer layer to be water tight and then no more having to spakle.
well… a few things:
I dunno how much a chemical bond would really do, being as it is a foam and not a solid you’re bonding to. The foam hasn’t really got enough strength that the far greater strength of a chemical bond would do any good. As has been mentioned, when you strip the glass off a board a thin layer of foam comes away with it. My read on that is that the mechanical bond of the glass/resin to the foam is just fine, but the foam itself fails. Tradeoff of lightness for foam strength, I guess. In the case of 1 lb/cu ft polystyrene foam, well, polystyrene itself runs around a density of 1.01 or so, circa 63 lbs per cubic foot. There’s not a helluva lot of of stuff there.
Then you have, well, I’ll call it the Marshmallow Fluff problem. See, I’d think that most chemical bonds involve similar structures, leastwise with organic molecules like resin and foam. As far as I know, anyhow. Problem is that when ya have that, you’ll likely have one acting as a solvent for the other. Which can be a problem, cos the foam is likely to soften and lose its structure. The example that jumps out at us is using polyester resin ( which contains styrenes ) on styrene foam.
Now, as Bert Burger and others have done, layering a denser foam over the lightweight foam core of a blank acts to do pretty much what you’re looking for, plus being denser it generally has less voids that require filling, etc. It also acts to spread load better than the very light ‘core’ foam, especially impact loads like heel dings and others that tend to cause delams. Probably be a helluva sight less permeable into the bargain.
Leastwise, that’s my read on it. And I surely have been wrong before…
hope that’s of use
doc…
Let me do a little somewhat out of the box thinking here…
What has been posted above is exactly the point and problem, and Greg Loehr has pointed it out too, that it’s the foam that fails. Okay, how to improve the bond, or to distribute the stress over a larger area, so the failure doesn’t happen?
One way, as noted, is a thin layer of denser foam. I suggest this is bit of an advanced technique for most of us.
Another way might be to score the foam so the resin penetrates and bonds better. Such as by dragging a row of blades across the surface of the finished blank… maybe 1/8 inch deep and 1/8 or 3/16 inch apart. It’s intended that the lam resin penetrate these scored cuts and distribute the bond, increase the bond area. Additionally, making tiny resin I-beams will increase the flexural stiffness.
Downside is that such a process would make the finished board heavier, and as we all know, every lighter product has led to a lighter, and inevitably weaker, board. Ask Grubby about the frustrations of this.
I don’t want to be a downer, or dissuade creative thinking, but I really suggest that we are at a plateau with respect to making surfboards, at least with the materials and techniques readily available to the backyard builder. The fringe experiments with EPS, XPS and whatever, but really don’t have a better backyard end product than industry-standard PU/PE surfboards. 'Scuse me, Greg and others using epoxy…
Uhmmm… going along with ‘thinking outside the box’…rather than vaccum laminating, what about laminating under mebbe a bit higher pressure? Do a lamination and then put it in some sort of container that was air-tight and then pressurise it, say a few PSI, so that the resin was driven into the foam just a wee bit better. You wouldn’t want so much pressure that you were crushing the foam, (which you’d have to experiment some to find for various foams ) but it might just give you a ‘thicker crust’ of foam/resin that would stiffen it up some, make it more ding resistant and all.
just playing with the ideas, y’know?
doc…
I have read that one of Dave Parmenter’s gripes is that many modern glass jobs are set off so hot and/or squeegeed so hard that resin is not allowed to penetrate into the foam far enough for a good bond. I tend to agree.
Michael J is on to something with his triple density foam composite blank but it is probably too complicated for most of us. The higher density foams are positioned deck side as a solution to the deck problems discussed. See diagram for details…
And then you have Thane Pope’s carbon fiber board that has a shell that is so strong, it doesn’t even need foam. It’s hollow, which illustrates an interesting point: It seems to me that in Polyurethane foam and Polystyrene foam boards you have varying degrees of strength from very weak (polystyrene), to middle weak(superlight and superblue polyurethane), to sort of weak (classic polyurethane).
The foam is not as much the issue in strength as is the shell that goes around it.
No matter how good the bond between foam and glass, the weak link will always give way first, and that’s the foam.
So as long as we use foam, we have to find the compromise that works for us in each new board. Heavy glass? Light glass? Heavy or light foam? Epoxy? Polyester?
This is too much fun thinking about all of this. And in the end we create functional sculpture that we haul to the beach and ride on waves with.
Counting my blessings. Doug
It might be interesting to try to make something that creates a chemical bond between, say, EPS & Divinycell. Smearing or spritzing some kind of catalyst between the two and then getting them into a vac bag (or a pressure chamber?) would be easier than cutting glass, mixing resin, laminating one side, putting on the other, taping it down, and then into the bag…
yep thats it …currently its the cores that are letting us down …ive never seen a problem with bonding …
the problem is always how well the foam bonds to itself , whenever ive done peel tests everyfoam will leave a layer of itself against the laminate …xps having the thinest layer removed , large beaded eps having the thickest layer removed …
the thinest glass jobs are easiest to peel , the thickest are hardest to peel …
a sandwich over large bead eps and youll never peel it , youve basically got to snap your board so badly so the thing is unrepairable and looks like its been blown up before you get something resembling a glass peel …
but then you come back to the surface layer , skin delamination under stress , starts to resemble the original problem again …
but this time we only have a few mm to deal with so tieing it together is not as much of a problem as tieing to a 3" thick piece of foam …
its possible to remove the core all together …
so far i havent been able to do that successfully and maintain performance …the skin stiffness required to go hollow , means the board tranfers energy that well the ride becomes over sensitive and doesnt allow heavy flexing in critical zones , no flex means no springback , no springback , means you cant capitalise on free energy …
its an endless search for durability , performance and asthetics …
for everyone, one of those 3 will be more important than the other 2 …
for me the priority is 1st performance , 2nd durability and 3rd asthetics …
for others the order could be different …
maybe we should be looking at a material where there is no mechanical bonds …
just a one piece foam you just shape and surf … no delams , because the whole thing is chemically one …
but then you come back to the performance issue …
i know from my point of view , certain mechanical bonds have been put in place to either stiffen one material or allow another more range of movement … with the aim of allowing the materials to work together to give greater ride characteristics …
bonding everything together may give greater stiffness or strength , but may not give a better performing board …
if it doesnt perform , then your looking at the entry level market , for anything you develop in this area …
give me a fibre reinforced liquid that acts as a liquid before it becomes a solid and dries to a mirror clear finish with no solvents and i’ll be happy …
spray on perfection thats light and strong …
regards
BERT
What Bert is saying is so true. The thing we are dealing with here is that the foam densities we are using are so light that true structure within the blank, as far as bonding to it, can’t really exist to any extent. They use urethane foam for transoms in boats and never have delaminations but they’re using 20 #+ densities.
As for EPS the bond is actually quite good, best of any of the foams typically used in boards. In fact deck delamination is not an issue with 2#density EPS at all. But the compression strength isn’t much better than urethane per weight. And whether urethane or EPS or XPS, the break strength (breakage is usually delamination under compression) is primarily determined by the stiffness of the skin (as noted above) and the density of the foam directly under the skin. Sailboards went to sandwich contraction about 20 years ago to solve break strength, probably where we’ll go soon because of performance/weight demands. This solves many issues. I’m sure Bert never sees his sandwich delaminate. He’s using a 5#+ select balsa cored epoxy laminate… virtually impossible to delaminate that.
As for hollow boards the foam core does have a purpose even if you could do without it. It gives the board better resonance, it bridges the gap between the rails without having to build in bulkheads, localizes impact loads and allows lighter interior laminates. The hollow boards we built required so much extra reinforcement inside that the boards usually came out heavier when hollow. The interior foam that is used inside the sandwich boards I’ve built, and the ones Bert builds, weighs less than a pound. Hard to make the case for leaving it empty when the foam gives as many advantages as it does and actually allows for lighter weighs overall. The real advantages to leaving it hollow are that it’s easier to build and it can be drained easier.
Aquafiend65 wrote: “Different chemicals.”
This is not really the problem. The fact that there are different chemicals involved actually has little to do with board failure in regards to delamination between the resin fiberglass shell and the foam core.
The bond that forms between the resin fiberglass shell and the foam core of a surfboard is quite similar to that which forms between wood and glue, wherein both chemical and mechanical bonds are involved.
Mechanical bonds form when the resin (in a liquid state) flows into and fills small pores and spaces in the foam and then hardens around these microscopic structures.
Chemical bonds (known as ‘specific adhesion’) form at a molecular level as a result of the attraction between the resin and the foam due to their opposite electrical charges. Please note that this does not require the resin to dissolve the foam (something which is actually highly undesirable), only that there be an electrical attraction between the foam and resin molecules, both of which retain their structural, that is to say, chemical, integrity (in other words, no new types of molecules are created).
Since strong chemical bonding occurs between resin and fiberglass cloth, I see no reason why the same thing should not occur between resin and foam.
A chemical bond is typically much stronger than a mechanical bond, but at the same time there are usually (at least in wood glue joints, anyways) many more mechanical bonds than there are chemical bonds.
I suspect that what happens when a board breaks dues to delamination is that the board is flexed and overstressed to the point where eventually the mechanical bonds between the resin, fiberglass cloth, and foam fail first and the chemical bonds (of which there are fewer), are then not strong enough to hold it together after the breaking point (of the mechanical bonds) has been reached.
“The best you can hope for is a good mechanical bond, which a good epoxy gives you.” - Aquafiend65
Although epoxy resin may form a stronger mechanical bond than does polyester resin, its real strength lies in the fact that epoxy resin alone (that is, without any fiberglass cloth), is much more resilient, stronger, and able to withstand bending and flexing stresses than is polyester resin, which tends to be brittle and weak in comparison. (To put it in technical terms, epoxy resin has a greater ‘modulus’ than polyester resin.)
In addition, the chemical bonds between the epoxy molecules and the fiberglass cloth are much, much, much stronger than are those between polyester resin and fiberglass cloth (something like four times as strong), and thus able to withstand a much higher degree of flexing, stretching, and stress before failing.
So while epoxy resin may form stronger mechanical bonds than does polyester resin, in regards to delaminations (that is, the strength of the bond between the resin fiberglass shell and the foam core), the chemical bonds play as (if not more) important a role than do the mechanical bonds.
However, if the weak point of the board is the foam itself (that is, cohesion between molecules within the foam, not between the foam and the resin fiberglass shell, fails), then theoretically even epoxy resins, with their stronger chemical and mechanical bonds, would not be of much help in preventing board failure.
But because epoxy resin has a much higher modulus than does polyester resin and can thus bend and stretch to a far greater degree along with the board’s core when it bends and flexes, epoxy resin will maintain both its mechanical and chemical bonds (with the core) well beyond the point where polyester resin ordinarily fails.
id be more inclined to say , the resin glass combo is still a mechanical bond …
just like the steel mesh in a concrete pad would be mechanical …
the resin encapsulates the weave to form a mechanical bond …
one reason i say this , if you get a peice of resin saturated glass and smash it with a hammer , you can smash the resin appart and break it off the glass and retrieve your glass , even tho its mangled and of no use …
similarly you could smash the concrete off steel mesh …
also greg , i can still get delamination with balsa once i cross a certain weight threshold , and that problem is mainly caused by extreme flexing allowing more shear force and then even the wood will fail under those conditions , that being said tho , everything else fails sooner , so the timber does allow me to go more extreme in how light i can push things …
speaking of light …im working on something new at the moment …
which is probably the first sizable forward steping breakthrough ive made in years …
even tho ive been able to do this in 8’ plus boards for a long time , that is make a finished board lighter than a shaped urethane blank …
ive just successfully been able to make 6’ x 18 board weigh in finished , the same weight as a shaped urethane blank of the same size …1.6 kg and i cant even pressure dent it …
that pretty much blows urethane away for use in a performance board , when i can make a finished board weigh less than foam …
i can guarantee this one is gonna blow them away …
i just made myself a new small wave groveler in the same method 6’-6" x 22 , 2.3 kg , also both these boards have set fins …
quietly confident about this one …
regards
BERT
Great post retroman. What he’s saying is exactly right. Epoxy has better adhesion characteristics because it sets up a better chemical bond because of opposite electrical charges at the resin/foam/glass interface … and this is true with virtually anything it’s in contact with. Hence, it’s popularity as a glue. It’s also better able to handle stress loads because it holds things together better and forces all the parts to react as one unit. Stress loads are shared by all components and the better they’re held togather, the stronger the overall composite. And finally, the added adhesive qualities improve the composites resistance to fatigue.
Again most boards fail as a result of delamination under compression which is seen as a buckle of the glass. 90% or more. Generally this is a failure within the foam itself and not the failure of the foam/glass/resin interface. The foam is shearing from itself. The solution to this is to, 1. stiffen the laminate thereby reducing the load on the very light core foams that can’t handle the stress or 2. by increasing the corefoam weight to allow it to share the loads. The first will add weight unless it’s done using sandwich construction and the second adds weight unless you minimize the heavier core foam by use of a sandwich construction. Mmmmm, seems for the ultimate in high performance there is one overall answer.
There is a question then of just how many surfers need the ultimate. Many do, perhaps many more don’t. This leads to product specialtys for different end users which is something we’re now seeing the beginnings of in the marketplace.
So the issue is the poor shear strength of the foam at the epoxy impregnated foam/unimpregnated foam interface. Increasing the density (weight) of the foam is a good alternative. If you look at the foam from an elemental point of view, we would be increasing the strength of each ligament of the foam by increasing its robustness.
What about alternative foam materials? Couldn’t we decrease the relative density of the foam to maybe 2-3% and utilize a ceramic/metal that has a higher material density and has better mechanical properties as a foam structure? Maybe we could combine that with a lighter plastic foam core in a sandwich structure, save weight, and have a stronger board?
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maybe we should be looking at a material where there is no mechanical bonds …
just a one piece foam you just shape and surf … no delams , because the whole thing is chemically one …
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Yeah, we could grow it and harvest it…I’m gonna call it a tree;)
Hey Bert, Greg or anyone, have any of you tried using 1mm coremat? I know it’d suck up a fair bit o’ resin but it’d give you a thick outer shell.
I’d agree - when you burn a glass/resin laminate, you get glass cloth plus a certain amount of soot and the glass fibers themselves look ( superficially anyhow) pretty good. If there was any real amount of chemical bond, I’d expect to see something like charring and destruction of fibers, no?
Likewise, in dings you see the cloth fiber structure with any substantial crushes- the resin appears to break loose pretty easily.
With the balsa, like the foam, it’s the substrate that fails, not the lamination itself. With balsa or any wood, I’ve found that it gets a helluva sight worse when the stuff has gotten wet. Encapsulate it really well, that’s something else again.
And dammit, Bert - when you get going about the new stuff, you get me awfully curious and running possibilities through my head about just how you are doing things. None of which are likely to be even close, but then again that’s the fun of it all.
doc…
Resin, whether epoxy or polyester, does indeed form a chemical bond with both fiberglass and foam. And it is this chemical bond, along with the fiberglass being imbedded in a matrix formed by the resin, which gives the resin fiberglass laminate whatever strength it possesses. But you needn’t take my (and Greg Loehr’s) word for it.
An extremely extensive and comprehensive web site about polymers, including epoxy and polyester resins, what they are and how they work, can be found at http://www.psrc.usm.edu/macrog/floor2.htm
This is by far the best web site I have found on this subject and contains tons of technical information about polymers written in a way that is both entertaining and accessible to the educated layman (e.g., someone with a basic understanding of chemistry). If you are at all interested in understanding what is going on with resins you will want to bookmark this site, as you will be visiting it more than once. (It also has very good info on composites, which is technically what a simple resin fiberglass laminate is).
As to the experiments that Bert and Doc performed which they believe demonstrated that resin does not form a chemical bond with fiberglass, well I am not a materials scientist but I will hazard a couple of guesses as to what is going on that led them to their erroneous conclusions.
- In the case of burning the resin fiberglass laminate (not advisable due to the toxic fumes produced):
Remember, a chemical bond is an electrical attraction between two molecules with opposite charges. The two substances still retain their unique molecular identities and can be separated back into their individual constituent parts.
A chemical bond can be broken, that is to say, the two molecules separated, in a variety of ways. One way is through application of a solvent, such as water or acetone. Another is through the application of heat (how much heat is needed to break the chemical bond is a function of how strong the electrical attraction is).
Thus when the resin fiberglass laminate was burned the heat produced by the fire broke the chemical bonds and merely drove the resin molecules and fiberglass apart!
A good example of a chemical (i.e., electrical) bond easily dissolved by a weak solvent is sugar. The reason sugar feels sticky is because it forms a chemical bond with your skin! But this bond is easily broken and simple plain water (a weak solvent) can be used to wash it off. In the case of substances that form a strong chemical bond with your skin (e.g., polyester resin) a solvent much stronger than water (e.g., acetone), is needed to remove it.
In addition, resins have an upper heat limit beyond which they fail, and burning the resin fiberglass laminate definitely surpassed that heat boundary.
Indeed, the resin would have been consumed by the fire whereas the fiberglass would not. Fiberglass is actually composed of the same substance as found in the windows of your car, house, etc. That’s why it’s called glass! Have you ever tried to burn glass? It just can’t be done. You may be able to melt it, but you cannot burn it.
- In the case of mechanically separating the resin from the fiberglass:
I suspect that resin molecules still adhered strongly to the fiberglass, but since this occurred on a microscopic level and I assume you did not examine the glass at this level (i.e., with a microscope) you were unaware of their presence.
An alternative explanation would be that tiny shards of fiberglass sheared off and remained imbedded in the resin. Although the fiberglass may have seemed like it was wholly intact to the point where it could (almost) be reused, I doubt that this was really the case. (In any event, I have no doubt whatsoever that the resin was entirely unusable.)
Did you examine either the fiberglass or the resin under a microscope?
But like I said, don’t take my word for any of this. I am by no means an expert, just someone who was curious enough about polymers (and with a basic knowledge if chemistry) to do some independent research (i.e., read up a bit on the subject). So go to the web site I referenced above and enter the fascinating world of polymers! Hey, they’re all around us, and we ride waves upon them, so we might as well learn as much as we can about them!
P.S. Another thing about epoxy that makes it superior to polyester is that epoxy resin is waterproof, while polyester resin is not!