Current thoughts on using a vent on eps

  Okay, I forget, where do we stand on using a vent on EPS?

I’m using 2lb. foam from a local architecture/construction supplier. Couple SUP’s, and a few surfboards. So far I haven’t used any type of vents. I try to be cautious keeping the boards from overheating in the sun or inside a car, etc.

 My latest (6’10 quad) had a spot about 4" around pop up on the deck the first time it was stashed in a car (although shouldn’t have been dangerously hot). When I cut out the problem area the glass was sticky/ not cured. I think I must have allowed a little bit of poorly mixed resin on my first lamination and then my filler coat hardened over it. I never realized it was a problem spot and finished the board with a cheater coat also. I know a vent would not have helped in that situation!

 Just got me wondering what is the consensus on Sway’s concerning vents.

 Obviously, most interested in opinion from Shaper-o-holic-ness.

Generally, using most 2 pound foam you shouldn’t need a vent. Using the better surf intended foam with tight fusing of the beads you can skip the vent on 1.5 pound foam. I don’t use 1 pound anymore but if I did I would drink Dos X’s. No wait. I would always use a vent no matter what.   Since many (most?) SUPs are made with 1 pound you’d want one there as well. 

Greg is right…1.5 lb and up doesn’t need a vent.  I build a few SUPs here and there and generally use 1.5 lb Marko Foam EPS but use the FCS handle with an integrated vent so figure why not just drill the hole and screw in a vent?  Better safe than sorry, right?  You should be fine without one on 2 lb. foam.



I have a Goretex vent/leash plug from Greenlight in my current project. I stuck it in the top more or less over the thickest/widest part of the board, figuring that would be the spot where it might want to delam (lots of foam single layers of cloth). All things considered (me the rookie glasser, 1.5# foam ) I thought it would not hurt.  The leash will be anchored through an epoxied hole in the blocking by the long box.

I shaped two boards from 2 pound eps, neither of which have a vent. One mainly saw it’s use in winter, but the other survived the rather hot summer last year without exploding. 

Exploding EPS hasn’t happened at least since last year. It’s pretty safe these says. 

i use 2lb. 

my every day board lived in my car all summer (temps up to 40C so probably 50-60C in the car on the hot days), and has been surfed over 150 times over the last 12 months and no vent related issues at all.

Just want to add the noob perspective…

I’ve only done a couple of EPS boards but the first one delammed badly, and I’m still in the process of surfing it, discovering new delams, and fixing them.  Maybe it was the volume of the board (I’m 205 lbs, this is a “Big Guy” hybrid shortboard based on a CI Whip, 6-7 length, about 44 liters volume, with thick rails), maybe it was in part that I colored it dark blue, maybe it was that I got a little water in the board at the start when I blew out a fin box making a bottom turn (again, this was my first EPS board, and I used fast RR for the Proboxes, not knowing any better).

Anyhow, all the details that added up to create the world’s most delamming EPS board:

Blank:  US Blanks 1.5 lb open cell EPS

Glassing/color schedule:

  • spackle

  • Montana Gold (very dark blue) directly on sanded spackle/blank (Montana Gold will melt the US Blanks 1.5lb – I didn’t notice this the first time using it, but did yesterday painting a second US Blanks 1.5lb EPS – maybe someone expert can weigh in on whether this paint might have been part of the problem).

  • 2 squeegee coats, Resin Research (fast cure catalyst – 2 because 1st one fisheyed), lightly sanded before lamming

  • 6 oz e-cloth with 4 oz finbox patch, bottom; 2 x 6oz deck; Resin Research (fast)

  • Hotcoat:  Resin Research (fast)

  • Glosscoat:  Krylon clear, rattle can (was impatient to put the board in the water)


No idea if I got something done poorly in the pre-lam stages, but the board gets hot and starts gassing very quickly if any sun at all hits it (noticeable when draining the board after the fin box fiasco).  I bought one more EPS blank of the same type (US Blanks 1.5lb), shaping it into a similar board with a bit less volume, maybe 42-44 liters, and have followed almost the same glassing schedule, except that after spackling and painting I’m doing a Zerovoc coat in the hopes of getting better spackle/paint/sealing-coat adhesion.

The (delamming) board itself surfs great – bummer since it seems there’s no way to stop the delamming, as I’m seeing it all over the board.  One noob vote for putting a vent in any 1.5lb US Blanks EPS that has any volume to it, based on limited experience, and cluelessness as to what I may have done wrong to exacerbate delamming issues.

Delams on EPS , no matter what density you use , are usually a surface bonding issue , not an expansion issue . Don’t cut corners , and let ALL epoxy cure properly and you’ll be fine…the surf industry in general has a weird obsession with “flip times”…(lol)

Dark color is “dangerous” with eps. Paint on blank need to be really thin, spackle too. Don t wait between your resin on blank and laminate, do it in one go. Use denser blanks with light stringer, they are stronger and surf better. For plain color go with pigmented resin. 

I am sorry to hear about the troubles you are having. I would check the MSDS (material safety data sheet) for the paint, even if it says acrylic. If it has acetone or any stronger solvents it will mess with the EPS.
Has anyone quantified a minimum bond/peel strength for fiberglass and resin on EPS to prevent this sort of delam? it would be interesting to have a number and a method to use for testing samples.

Thanks for the feedback, guys.  For what it’s worth, I fully suspect it was the combination of the Montana Gold causing some foam melt and the dark color creating stress on it when the board was in the sun, although I never allowed the board to sit and really get hot other than when it was draining and had leaks for venting (post box-blow-out).

I used Montana Gold on an EPS recently – have posted about it elsewhere today – and it definitely caused foam melt anywhere it could contact EPS foam and stay wet for more than an instant; in other words, anywhere a drip occurred, the MG melted a small hole in the EPS until it dried.

Won’t be using MG on EPS any more, or using dark colors when painting EPS.  On any “big guy” boards that have some volume to them, for 1.5lb open cell US Blanks I’m going to use vents.  I did make a 32-34 liter board from the same blank material for a buddy – also with Montana Gold but with far less noticeable melt (I probably didn’t sand the spackle as…vigorously?) – and it seems to be OK.