Help with foam collapse

Hi everyone. Im about to start work on my second board and wanted to address some issues that came up with my first board. The biggest problem I have had, has been that the foam in the middle of the board collapsed after only a couple of months. It was mostly just on one side, right under where my butt sits. It collapsed about an inch, around football size. Board is now 3yrs old and the only other foam issue is that there is a slightly raised ridge created by the stringer on the bottom of the board. Im wondering if this was from something I did wrong, or possilbly just an unlucky blank. The board was shaped from a standard density USBlank and glassed 4oz+4oz on the deck and 4oz on the bottom using PU Solarez. I feel like it may be a bit overkill, but im thinking the next board should be eps with epoxy and 4+6 deck and 6 bottom. Would this solve the issues I have experienced? I have attached pics of board when initially glassed, and then pics of the collapsed area. Ignore the repair, that was a whole different issue.

EDIT: Thanks everyone for the suggestions. I cant actually respond to posts yet. The deck collapsed long before the repair was made, so its not a case of water seeping in. I think it was probably from shaving too much foam off of the deck and too light of a glassing schedule. Looks like next board will be 3 layers of 4oz on the deck and keep it out of the sun.

Well the bottom isn’t the problem, so stay with 4oz there, IMO.  Maybe use 4oz S-glass instead of E-glass.  PU foam gets less dense as you move away from the outside toward the inside of the foam.  I’ve always skinned the deck, then worked from the bottom of PU blanks to get very close to my final thickness.  This leaves more dense foam toward the deck.  Also, 4/4 deck schedule is very light for recreational surfers.  Full 4oz ‘E’ deck + 6oz ‘S’ patch will help.  With all that, maybe you got a bad or mislabeled blank.

While epoxy is great for laminating, nothing wrong with a good poly lam.

My shapes are a mix of PU/epoxy and EPS/epoxy.  I only repair in polyester resin, if needed.

That’s all I got.  Good luck!

Given that it’s a PU blank, I’d guess you took too much foam off the deck side. Gunkie is right about depth vs density. Always best to retain as much of the ‘shell’ on the deck side with PU blanks… I’d also suggest doing a deck patch in the areas most prone to compression, and lay the glass on the bias. IOW, put the weave at a 45 degree angle to the stringer. Three layers of 4 oz are better than two layers of 6. Especially if the cloth is not oriented in parallel layers.

did you guys notice that he’s talking about the bottom of the board?

Did you miss this part?

“the foam in the middle of the board collapsed after only a couple of months. It was mostly just on one side, right under where my butt sits.”

I’ve never seen anyone sit on the bottom.

the only board I’ve seen do that was shaped with an Ice9 blank and left briefly in the sun causing the foam to shrink.

If you wanted to save that first board Fiberglass Hawaii hasa really great video on doing a repair to a collapsed deck.  

WTF…you bought or made a disposable surfboard with 2x4 top…what did you expect?   Then maybe you over sanded it…or pulled the lam too dry.  There is 100 ways to F-up a surfboard.

Also…you are sitting too much, start surfing. All the dents should be under your feet…everybody knows that silly boy…I’t gonna get worse. Next time if you want a surfboard that will last do a 6/4 or 6/6 top. Add up the glass 4x2 = 8.  6 x 2 = 12  thats the amount of glass you have.  If you don’t want 6x2…then do 4x3…that strong right boy…4x3 thats strong.  Like Mr T strong.


Actually, if you look again at the pictures this was a case of foam shrinkage not dentage.

I happened to a board I shaped (shrunk the foam, same as the bottom of your board), It got cooked in the sun on a hot day. It also happens to most shortboards after a period of time. Gunkie is right aswell, this will happen faster if you take off too much foam. Keep the board cool and out of the sun and it should be fine though. Also make sure you are not sanding through the glass after your hot coat.

Good luck with the next one, Felix

True.    Good eye, Mako.

Look at the colour of it where you have the problem, its all around the area of that repair, water got in the board and that has messed with the cell structure in that area. Its possible that you repaired it without letting it dry properly. By the general colour of the board it also looks like its been left in the sun (if its relatively new) Water ingression is bad, water ingression and sun exposure is very bad. But water getting in to the foam is your problem here IMO.

On second look, It does look like it could be pretty sun-baked as well. 


I’m getting a litle different take on this - going by the pictures, regarding the deck could be a number of things - too low density blank, shitty blank, especially if it happened on one side of you ass only - unless you sit to one side on the board. Re the bottom - seems like a case of the stringer not being brought down enough  after fine sanding. That’s my take viewing the pictures - might have a different opinion if I saw the board.

Overshaped blank. Deck crushed from light glass job ,big butt ,heavy feet. Water got into stringer causing expansion of stringer…the foam did not shrink


The reason why its only on one side is because its a bit more difficult for water ingression to pass for the other side of the stringer, takes more time to travel. It looks to me that the issue is related to the ‘unrelated repair’ if its not compression dents and its only localized shrinkage then that is your problem.

Water ingression could be causing a slightly swelled stringer as well like stingray said.

Gonna add this to the deal. To my eye it looks like you left your stringer high  on the original shape. The damage 3yrs later is what happens when you leave a “high stick” foam goes down stick stays up cracks form water gets in foam goes bad vicious circle. Next board you shape make sure the stringer is flush with foam. when you run your hand back and forth, side to side, you should not feel a high stringer. That and if you want a board to last more than a few months glass a little heavier.