Numerous pressure dings on 3 new boards: a worrisome trend?

6/4 deck, single 4 bottom...they call it "standard" glassing & the lam is a big "S" instead of the UL. that's stock for 6'6" up to 7'6" (i think), then it's 6/6 deck, single 6 bottom.

edit: this applies to CI boards only. can't speak to any of the other big name builders.

 

Thanks bro. Preciate the deets.

 

epoxy is the answer, whether it be over eps or polyurethane foam.

Anyway, from what I gather, modern foam is significantly more dense than it was back in the Clark days, so I'm guessing your glass jobs are mainly to blame.

Just be careful with polyester - in an effort to make a longer lasting board, you're inadvertently gonna end up with a heavy board. Think balance.

 

Another factor may be the density of the foam. Foam molders are always trying to decrease their material costs by cheating on foam density. Meaning a 1 lb EPS foam board is likely a nominal .90 or .95/lb. Marko foam has different blank offerings.

Extruded PU (polyester polyurethane) can have the same issue depending upon the amount of blowing agent used. Although, the PU foam I've seen look to be fairly consistent and solid.

You can see the same thing in extruded polystyrene. This is actually Stryofoam. Styrofoam is a Dow trademark for blueboard insulation material. It's extruded PS.

EPS is what is used for coffee cups, cheap coolers or packaging. I have to wonder if some of the energy management characteristics of EPS cause it to deflect upon impact, creating a void that causes a pressure ding?

 

heres' an idea - why not abandon technology developed during the '60's?

in the 80's i had a cell phone that needed a briefcase to operate....

 

The vast majority of what people refer to as "epoxy" boards are epoxy resin over expanded polystyrene foam (EPS). Extruded polystyrene foam requires additional surface prep before glassing to avoid delamination issues. The quality of EPS has gotten better in recent years, as blank manufacturers continue to develop better ways to get different sized beads to "puzzle piece" together and fuse more tightly. As this technology improves, the result is a lighter, stronger blank, even at lower densities. Compared to polyurethane foam, EPS is less prone to pressure denting because the foam beads flatten when compressed, but then bounce back. You can see this with cooler foam or foam packaging as well. Higher density EPS is less prone to denting to begin with, and still bounces back to its original shape quite well. Because EPS is lighter than PU, board builders can use heavier glass schedules and end up with the same, or lighter, weight board. What you're left with is a blank that does not dent easily, keeps it's bond between the foam and glass better, and has a stronger skin for the same weight.

PU foam, on the other hand, is a rigid material, made from hollow bubbles with thin, solid walls. When compressed, the solid material crushes into dust, and you're left with a dent that will eventually delaminate, as the bond between solid foam and solid skin is compromised. Cut away a delaminated section of deck, and you'll see all the dust underneath. The lighter the blank (all foam comes in different densities, both PU and EPS) the less rigid material there is in the foam, and the more air bubbles there are... so it's even more prone to crushing. Because PU foam is generally a heavier material than EPS foam, board builders are more likely to use lighter glass schedules to keep the boards light and high performance. What you're left with is a board that has a low density foam that's prone to crushing, and a lighter, thinner skin that does not protect the delicate foam underneath very effectively. This board will dent easily and ultimately delaminate. But it's fast and cheap to produce, perpetuates the buy/destroy/replace cycle, tints beautifully, polishes to a mirror finish, and it's what we're used to.

 

LBCrew is that same softness of PU why we like its performance and responsiveness? For example, does stiffness/strength of a board correlate with an increase in dead feeling?

 

in my experience, yes. though i wouldn't call it "softness" so much as "flex"...PU is a more flexible foam. this is why poly boards will crease or buckle before breaking & EPS boards will just break.
i've had a few EPS/epoxy boards that were carbon copies of boards i loved (in poly) & i hated them. they had that "dead" feeling you're referring to, & lacked "pop" in turns. i rode the boards a dozen, maybe 2 dozen times, & got rid of them...these were traditionally made boards, just w/ EPS foam & epoxy resin. 4/4 deck, single 4 bottom glassing. they certainly held up better than their poly cousins; the decks were nearly pristine when i cleaned the wax off them, & i tend to be heavy on feet. but that wasn't enough (for me) to cancel out what i felt to be a stiff, horrible ride.

 

Okay, I understand LB crew's approach. But NJ42, what is this overshaping hypothesis? A few people mentioned it.

Do PU blanks really have varying density (or some other strength characteristic), from high to low as you go from the exterior to interior? I believe shapers can order blanks that are closer to the board's intended specs, but if this exterior/core strength issue was from manufacturing foam, it could remain nonetheless.

Still, even if a board was made with a Jello blank, it would be dent resistant with a heavy enough glass job, no? (I'm thinking of a fiber-mat Dinghy here). I don't understand how 'overshaping' would result in a softer deck.

 

yea, poly blanks tend to have a "tough" outer shell around a softer inner core & this can be removed if the shaper takes the blank down too far to get a desired thickness from a blank at a certain length. the idea is not to shape through that. higher quality foam (more expensive blanks) don't have this problem as much, which is why we still see it a lot on cheap poly boards that come from overseas...cheap blanks=cheaper final product. the development & use of close tolerance blanks (a blank that is close to the intended finished board) helped minimize this problem as well, but it doesn't always work out.
& you're not wrong...if you glass a crappy blank heavy enough, you'll get a dent resistant boards, but it'd be so heavy no one would want to ride it. & that's part of the problem...a poly board, glassed heavier & taken care of, will last forever. but we've had it drilled into our heads that we "need" the lightest glass job possible, & so that, combined w/ ****ty foam, results in a board that rides great for 6 months, then breaks, delams, or is dented & dinged all to hell. just in time for the latest, greatest model to drop in your local shop's boardroom. even a decent blank, glassed excessively light, won't hold up over time. back in the 80s, "ultra light" glassing meant a 6/4 deck w/ a single 4 bottom. now it's a 4/4 deck & a single 4 bottom...& i've heard some regional pros complain that even THAT is too heavy! thinner, more refined boards the take a comparatively heavier load w/ less structural reinforcement from a lighter glass job=a substantially less durable board, just from dropping 2oz in glass weight.

 

Couple things to think about...

You can't overshape EPS... it has uniform density, unlike all PU foam blanks, to one degree or another. There's ways to deal with that, like close tolerance blanks, or matching the DECK rockers, at least. You can take an oversized blank for the desired board, skin the deck, and overshape the crap out of the bottoms to get the bottom rocker and thickness you're after.. I've done it many, many times. You do end up overshaping the rails, but you just cut your laps a little wider and wrap all the layers.

Regarding flex... the flex of any single material alone tells you nothing about the the final flex of the finished board. For example, the blank itself... a material is only as flexible as it's stiffest part. In a blank's case, that's usually the stringer. Put identical stringers in identically shaped PU and EPS blank, and the flex will be almost identical as well. However, the two board will dampen vibration differently, due to the resonance of the foams and their different abilities to absorb vibration. Now wrap both boards in the same weight glass, and use different resins... again you have added another variable that changes the way the board will flex. Poly resin is pretty standard in terms of it's tensile and flextural strengths. But epoxy can be formulated to engineer a board's flex to be whatever you want it to be. In fact, you can use different resin combinations in a single board... use stiffer resin on the deck (to resist denting) and use flexier resin on the bottom... or in the tail... or wherever you want flex.

Then there's the difference between flex and "flex return"... the pop we all want in our boards... which has little to do with flex. Paper is flexible, but has no flex return. A wood stringer is relatively stiff when placed vertically between the two sides of foam, but it has excellent flex return, or "memory." So looking at the data when materials are tested in isolation is of little importance to board builders. It's the combination of those materials and how they are applied to the given design of the shape that means everything.