Hey.
Im making my first surfboard and im not sure on what foam to use for the blank. Polyutherene or EPS?
What are the pros and cons of each? and what would you advise?
cheers
It’s a toss up dependig upon where you are located and ease of securing available materials.
PU (polyurethane) foam is the most commonly found material for surfboards. The blanks run around $50 to $100 depending upon what size you get. They are fairly close to a finish shape so without power tools an extensive amount of work is saved as well as a waste of material.
PU blanks offer you the option of using catalyzed or UV activated resin. The catalyst (MEK) is a hardener that cures the resin and you must laminate the fiberglass to the board in a specific amount of time relative to the amount of carefully prescribed catalyst that you add to the resin. Hardening times are quite variable depending upon temperature, humidty, and even the container holding the catlyzed resin in. This is very tricky, and takes a lot of time for profesisonal glassers to get it down.
OTOH, U.V. activated resin gives you unlimited time to glass the board because you do it in an area away from outdoors light. Once you are happy with your result, you take the board to a curing rack outside, roll up your garage door or what have you and the curing process begins. Curing results over a period of approximately 5 to 10 minutes depending upon the amount of ultraviolet on any given day. This resin is premixed and removes the expertise of mixing catalyst into it.
Anyone that has ever had resin harden before they were done glassing their surfboard, can tell you what a bummer it is to have happen.
The other option is to use EPS foam (Expandable Polystyrene aka Styrofoam, a trade name). This requires glassing with epoxy resin. Epoxy resin is carefully mixed with hardener in pre-established ratios like 2 to 1 or 5 to 2 parts of resin and hardener. High grade epoxies are a solid and yield very high strength products. They are generally more expensive than polyester resins that are used on PU blanks. Because of the strength they yield, some builders prefer to glass their PU blanks with epoxy. The viscosity of epoxy allows easy wetting out (saturation) of the fiberglass being laminated to the board. Cure time vary depending upon if you use fast or slow epoxy hardener. A fast hardener generally allows you 20 minutes working time depending upon air temperature and humidty.
The most obvious pro to using epoxy and EPS is superior weight to strength ratio. The core of EPS blanks are far lighter than PU, and the weight of the board is concentrated throughout the fiberglass skin. EPS also has what is commonly known as memory because the blank can take dull blows or pressure from blunt objects, knees or heels, and spring back without a permanent dent. Polyurethane blanks, OTOH, have a fixed cell structure that once the cell wall dents, stays dented from crushing.
PU’s resist water in a different manner than EPS. Because they have a distinct cell structure, when the fiberglass skin is breached, water absorption is resisted due to its closed cell nature. PU surfboards can be surfed with the damage for a longer period of time without gaining extensive water weight. EPS however, although also closed celled, is comprised of round balls, that are formed from pentane and steam and adhered together in a secondary steaming process. The material has a significantly higher amount of air to material in it compared to a PU blank, and once the skin is broken water more easily invades and stays trapped within the EPS blank. Picture balls adhered together versus cells like a beehive.
New technologies have and are being developed to address EPS’s vulnerability to water invasion, but for the most part PU blanks remain superior in this department. Claims are being made to the contrary by EPS blank manufacturers but at the time of my writing this, I have not seen conclusive proof. Most of the new terms bandied about EPS blanks is marketing hype.
I use both materials extensively. I like and admire both types of materials for their inherent advantages. For the layman, EPS and epoxy have become more user friendly than ever before. Close tolerance PU blanks and polyester resins (paticularly UV resin) is probably the easiest, and most cost effective way for you to build your first surfboard.
I hope this helps you in forming your decision on what material to use.
An absolute ‘‘tour de force’’ comment. Well done!
I like your accessment!
Damn! Mind if I blatantly plagerize your comment, and use it for my college thesis? 
Mahalo,
J.D.
You’re going to plagerize me? Hmmmmmmmm, ok!
Just promise me you try to use “me” and “I” in your daily speaking, in the proper order…it’s rare these days!
mahalo for such a well explained article,really.In your opinion,does UV resin and catalyzed resin yield the same product? the reason I ask is because I had a board that the shaper told me no need to wait for it to cure before surfing,since it was UV cured.So I probably surfed it a week after it was finished(sand polished),and the deck was all pushed down already after that first session(4 hours,north shore)The shaper blamed the blank(King Mac) but I always wondered about the UV resin,that a lot of guys use now,'cause easier.Next board from same shaper,different blank,catalysed resin, ,I let this one cure 2 months after I got it,holds up almost like they used too.Could be the blank,the curing time ,but how about that UV resin?I noticed the UV resin fix dings kit,the stuff gets weird on your board after a while.Am I imagining things,what do you pros think of the UV resin?
PU is quite a bit easier to shape but heavier and much easier to ding if you bump it while shaping. Also if you choose EPS you will have to use either epoxy or resinx for glassing. No polyester resin for EPS! EPS is lighter and much less prone to damage but much less forgiving when it comes to finishing off the shape. Beads tear much easier you know.
EPS blanks also tend to be more expensive than PU blanks in my experience and are also harder to obtain. You’ll also find a better selection of rockers in PU as EPS has not been used all that much for shaping in prior years if not decades. So I’d probably go with PU if you’re shaping your first one.
First, that was one hell of an informative response that DS offered up. Truly showing that Sways is a great place.
To address your UV cure question, kava, IMO UV poly IS stronger. If you do a search on it, you’ll see where myself
and others have talked about the reasons for this. Basically it’s longer polymer chains formed, a more complete linkage
into a solid. But the difference in yield on a light glass job is going to be miniscule. Your board-to-board variance is most
likely from another factor, probably the foam.
Thanks MD and all…
I agree with your statement on UV resin…I use it a lot. It’s great for those one day boards. Resin is a plastic. That’s why I said it “cures” versus dry…when resin cures it is inert plastic. I suppose many of us would like to think of surfboards as more earthy, but I have to say the composition ‘ain’t’ so.
We are leaving out one of the most important ingredients here" fiberglass! This is THE reinforcement that bonds with the foam of choice. If you go superlight on your glass, the core will crush easier, regardless of what foam you choose. There are multitudes of different types of weaves and weights, as well as configurations of fiberglass in which some are specifically designed to work better with epoxes over polyester. Then we have finishes on the cloth like Silane and Volan. Each consideration plays a key role in achieving the optimum result.
MD, myself, Barnnfield and others on this site have spent years acquiring this experience and information. Some of it is quite technical. You are very fortunate that we are willing to freely share the benefit of that wisdom.
Quote:
New technologies have and are being developed to address EPS’s vulnerability to water invasion, but for the most part PU blanks remain superior in this department. Claims are being made to the contrary by EPS blank manufacturers but at the time of my writing this, I have not seen conclusive proof. Most of the new terms bandied about EPS blanks is marketing hype.
this statement is pretty radical
surprised no ones jumped on it
eva the boardlady says a similar thing
funny how everyone around here refers to evas experience but convieniently neglects to notice her opinion on eps that hasnt got composite skins
…well, I said some in the past but G L enter to the discussion and proclaimed that that is not really true
so, like he s got tons of experience compared to me (years from the last time that I worked with EPS and now the epoxies with better quality…) I guessed that he s pretty right
Paul, let me clarify my statement.
I think your reaction is to figuring I was stating that new technoligies spoke only
in terms that the EPs would be reinforced by hand lamination of fiberglass much like polyurethane blanks. I should have clarified my statement better by adding that this meant technology through the addition of alternative skins such as PVC, Hi Density PU foams, wood veneers, Nida Core and other similar products that present a durable barrier between the EPS and water. I was trying to keep it simple for a beginner thinking about which foam he would use for making his first surfboard. So it didn’t really seem necessary for me to launch into an explanatory about vac bagging skins on EPS, use of chopper guns and gel coats or other methods.
Intrusion of water is always a concern when using EPS as you and I know. The air between the beads traps and holds water, and it is difficult to vacate all off the water once it has penetrated into the core. I had success during the sailboard era by creating a helicopter prop type centrifuge that once strapped in and juiced up worked pretty well. All this high tech stuff wash derived from a washing machine and seat belts from a car junk yard. (I’m saying high tech with tongue in cheek) Drill the holes and let her swing…even then it didn’t get ALL the water out,but it worked pretty well all in all. We just made sure that the plug in was well away from our contraption so we didn’t end up decapitated.
P.S. I’m unaware what Eva the board lady states about EPS…are you saying she aid something to the effect that water wouldn’t penetrate a breached EPS core? I would never make that claim!
she states wrt to eps epoxy (no cored skins)
Quote:
One of the many new single-skin fiberglass over EPS core boards. I don’t get it - all the extra cost and vulnerabilities of Epoxy, with mechanical properties worse than the old-fashioned glass board. At least those did not soak up water…
im agreeing with you
im inclined to believe for marketing sake test results of a lot of eps is not done wrt pressure differentials
i made a few boards out of 2 pound foam and glassed them
left them in the sun after a few dings and water started bubling out
gave up on it there and then
no reason to use it unless its in a composite
and eva has the same opinion ( according to her site)
i just glassed a pu blank in epoxy and it is cosmetically superior in every way to the eps ive seen (and im a novice)
id like to try a marko blank however 170$NZ for a piece of eps is daylight robbery imo
i can see its far cheaper to make boards in eps if you are constructing them yourself
but i dont believe they are superior to pu
or perhaps not so much better as to warrant changing
unless its from an environmental standpoint
i think if people want superior strentgh light boards they need to accept that composites are the way forward
and learn a cost effective way to manufacture them
water is far less an issue when skined with a high density foam
i would suggest that epoxy over PU would be the the best bet for home builder
no odour or solvents neccesary
Keep in mind there are some very good quality EPS foam manufacturers that produce quality high fusion foam that absorb virtually no water.
If you are trying to do it cheap and get it off the shelf from Joe Blogs, Home Depot, Bunnings, or the like, then you are not getting that level of quality.
Wildy & Greg.
Yes and no…what I mean is that I agree and somewhat disagree with the notion that all EPS be put in a category that is resigned to a Compsand type approach. As Wildy has stated there is a higher grade ‘super’ or “tightly” fused EPS that resists water pouring into the blank. It would be enlightening for you to elaborate a bit more on that. My understanding is that terms like Superfused or Surf Specific, are marketing terms, and this was said to me by someone experienced in the EPS blank industry (not G.L.) that shall remain anonymous.
I manufactured quite a few very durable 1.0 & 1.5 lb EPS sailboards (and some surfboards) throughout the 80’s that held up quite well and worked exceptionally well in light wind. Their ability to carry a heavier payload (rider, mast, boom, and high area sail) enabling them to get off the line and onto a plane. It is generallly held as common knowledge that the densities lighter than 2.0 lb. aren’t durable, yet these boards lasted for years and I would beg to differ with that opinion. Let us not forget that hand laminated hulls are also composites, and they can incorporate a wide variety of reinforcing materials other than just E glass.
The larger the board, or more correctly state, the bigger the volume, the more the weight savings using EPS imparts. This is particular evident in sailboards, SUP’s, and big high volume surfboards. The likelihood of dinging a double or triple glassed epoxy EPS hull isn’t a daily incident, and if the rider exercises caution, they can choose to get out of the water, seal the board with a waterproof tape or carry a tootsie roll epoxy stick and repair the board on the spot. So the argument for EPS being resigned to a compsand or vac bagged skin isn’t mandatory in my eyes.
I also want to mention that you will never see me making comments professing to know anything about compsands constructio as I know very little about them but I marvel at your ability to build them.
I’m interested in the fused foam as well…
I’ve been asking around about the water -absorbing characterictics of 1# mold-expanded fused EPS, but nobody seems to be able to give me an answer!
Maybe nobody really knows yet?
Seems like claims are definitely being made on 1.5# and higher, but no info for 1#.
Pauls point is very good, about pressure.
Do these foam manufacturers test by making a board in warm weather, take it into cold water, then puncture it?
Or jump up and down on it and create a diaphram pump?
The standard water test is something along the lines of “stick hunk of foam in water, see what happens”
Most EPS manufacturers claim their foam has very little water absorbtion, which is true for a bare block of foam.
Sealed inside a fibreglass pressure vessel is another thing altogether
I generally agree with that assessment…that’s why I said it is prudent to get out of the water when you get a ding and seal it before eposing to further water.
The obvious point here is that EPS has a high degree of air between the material. The more air the light the core, the more prone to water invasion when breached. However, the flip side of that is hat EPS opens up a lot more possiblities of reinforcing it due to its inherent lightweight nature.
Remember: for what you get, you give up something.
Adding outside skins to EPS has myriad p[ossiblities depending upon the material you choose to skin it with. You can sandwich it with some very durable lightweight materials while effecting an I Beam effect while doing so. In my book, the approach has tremendous value. As I said before, I admire both materials for their advantages and use each of them extensively…anohter feather in my quiver so to speak. I prefer to use a vocabulary lean on words like “never” and “only”.
The bottom line is IF you like the ride or not, and that, is susceptible to individual preference.
I fully agree with all that
It just would be nice if somebody had a definitive answer…
I’ll order a billet if I can get it in waterproof 1# !!
Until then, I gotta put my vote in for protecting the EPS as best you can, and a sandwich skin is top of that list.
I havn’t used marko or any of the high density EPS blanks, but visually they look like they would do the job, i was impressed.
No good for compsand unfortunately
I’ve noticed this with the Eps/Epoxy boards I’ve built:
Water travels further threw Eps. On some I’ve had the stringer wick water and swell. But, I have had dents pop back out with EPS.
Water doesn’t seem to travel as far in PU, but PU foam yellows and rots with exposure to water and UV much more easily. And, I can’t recall a dent healing it self.
As for CompSands, there are many different materials used in them and some are much more resistant to water damage. Balsa isn’t one of them.
My two cents…