EPS Glue/Hotwire Pics & Questions


Here’s the sitch. Glued up three sheets of 1 lb. Insulfoam with Gorilla Glue. First off, I was unable to spread the glue to get full coverage. It soaked into the foam almost immediately and the plastic spreader did little to spread the glue. Wiped down the opposite sheet with a wet rag. Wrapped all three 2’ X 8’ sheets together with plastic wrap and set on garage floor with 6’ composite table and marble tiles to weight it down. Left alone for 18 hrs then unwrapped and hotwired the top rocker.

Here’s where the fun begins. The glue did a pretty good job of resisting the hotwire, however the wire sliced perfectly through the foam. There is a section of foam that was not glued and may cause delam probs. This is my first multi layer hotwire so I’m not sure what it’s supposed to do.

Should the glue cover the entire surface of one sheet? If so, how is this accomplished with GG?

Will the separation in the sheets cause a problem in the future?

Any additional advice is welcomed.

I have no problem using this stack as a test and I figure that at the very least, I have hotwired a nice rocker bed for future boards. But, the $14 cost per blank and $18 per bottle of Gorilla Glue will soon prove expensive.

I’ll post one more…

Here’s the last one.

wow that’s happened to us when we used 5min epoxy and didn’t work fast enough.

We use those stiff dark orange plastic spreaders the smaller the better and really push down into the foam to spread the glue around. You should be able to get a good even coverage doing that versus the lines you ended up with. Gotta press hard though to lift the glue from the pores and move it around. I usually do tight small squiggly circles of glue as I spread it around and no need to glue too much outside of the outline you’ll be cutting unless you need the offcuts to press the rails on.

I think the hotwire issue is cause the glue is too thick in those lines. You really either need to squeegee it thin or lightly brush it on. Another option is to by one of these glue bottles at a woodcraft store with the roller on the end turn it upside down and roll the glue on the surface before squeegeeing it thin or lightly brushing it thin… You should have alot of work time cause its the water that activates it. We also completely soak the opposite side with a sponge the more water the better in my opinion cause you really want the glue to expand into all the pores between the sheets for a tight bond.

Sorry to hear about the delams but we use to have that with epoxy glue ups as well you really have to get rid of any glue ridges that will cause air pockets to get trapped which cause the delams…

Ola Senor!

I’ve had the same woes with glue-ups before; which glue to use, how will I cut through it and the resulting highs and lows (psychologically AND physically…on the blank that is) of this endeavor. I’ve also had two boards delam at sh*tty glue-up spots in the core, so I DO think it’s important that you have good adhesion there, especially if your board is going to withstand any elevated temperatures.

There’s a couple of ways around ever encountering glue in your lay-up; One method is to have both your rocker templates and outline templates handy; trace them out on your sheets of foam; both for the outline and for the profile, before you apply any glue. What you can then do is trace your templates on to the foam, giving you an area to spread your glue that you will not contact when you hotwire. Horizontal lines across the sheet from where your rocker template connects the sheet intersection will give you these boundaries. Sand the region between these lines down with some 60 or 100 grit to give the foam something to bite in to; spary the other sheet (that you’ve also sanded lightly) with a bit of water and you’re off to the races.

The other approach is one that you’ve already hinted at and I’ve found to be the best option; Lay up a rocker bed separate from the core manufacturing step. Easy peasy; you can put one together with scrap pieces of foam that you have left around from other projects; all you need to cut is that actual bottom; no deck cut required. Once you’ve got this taken care of, you’re laughing; grab a couple of sheets of foam such that the additive thickness will be enough for your board +~1/2". Trace the outline of the board on to the sheets; top and bottom, on both of them. Sand the inside area of this outline lightly. Take a small amount of epoxy and squeegee it over the outlined region. Place that sheet on your rockerbed; even use a piece of tape to insure you’ve got it in the right location. Then lay the next sheet overtop; tape it to the first. Now you’ve got your two sheets on top of your rockerbed. Slip the sheets, + rockerbed into the vac-bag and pump that sucker; check that nothing has slipped too far…go drink a beer and get a good nights sleep.

Next day, peel off the bag. What you should now have is the two sheets glued together, but the curve will be locked in to some degree. What you can NOW do is weight that puppy down onto the rockerbed again and set up your profile templates for hotwiring. You SHOULD be able to find a way to place them such that the seam between the two sheets exits exactly (or very close to) the tip and tail (better a seam on the deck than on the bottom). Screw the templates in to the foam and hotwire away. You should now have a blank with some (probably not all) of the rocker pre-locked. Because you’ve traced your outline already, you should be able to just take marking from the offcuts for tip and tail position, trace once more and cut the outline for your blank. Done.

Next is actual shaping. You can go a bunch of ways here; Benny1 would suggest that you shape the bottom, then vac on the bottom skin (if you’re sandwiching). Again, go back to your rockerbed to do this. Now that you have the glue-layer in the middle and a sandwich on the bottom, your rocker is locked, the board is pretrty stiff and you’re good to go with the rest of your shaping.

So, basically, that was just a really longwinded way of saying go buy some more foam and use the rockerbed that you just painstakingly made to save yourself having to deal with glu-lines in the shaping process and delams in the finished product. Glass, epoxy, finboxes and/or fins are the expensive part; the foam is not. Better to scrap and start over than finish a project that is doomed from step 1.


Oneula & GWN,

You’ve both given a lot of helpful information and I really appreciate it. Looks like I’ll be making another run to Lowes this evening. Do you need anything while I’m there? I swear the checkers already know my name.

I use 3M super 77 spray adhesive. Pick some up at Lowes. You can experiment with it, I have found that it bonds well and the hotwire cuts through it . It should give you a bond that is just as strong as the foam itself.

yeah kind of weird walking out with $200-$300 material tabs every weekend…

Makes you wonder that when you add it all up if it was all worth the grief…

6 yards of silver and blue texalium, a moldable 15" plexunas grit bar, a 7" fin and 50 yards of discounted seconds cloth ran me $275.00 last week at Fiberglass Hawaii… I could’ve bought a modified Clark planer they had on sale ahile back for that cost…

Yeah Homedepot, Lowes, Fiberglass Hawaii and Woodcraft know me well too.

It’s always…

Hey Mr. white collar looking dude what they hell are you making?, or what they hell are you doing here you don’t look like one of regular type of clients?

Super 77 has failed me before on 2 separate cores. Not recommended unless you plan on using the entire can…it doesn’t ever get hard; always stays kinda gummy and seems to wanna separate if the board builds up internal pressure. If you’re venting your boards, might not be a problem, but that’s 2 outta four boards that have delammed cause of the Super. I’m sticking to my guns; be careful where you put down your glue and make sure it doesn’t intersect anywhere your wire has to cut through…then use the strongest glue you can, regardless of whether you can hotwire it or not; it don’t matter if you don’t hit it.

'Neula…just don’t shave on Thursday and Friday; wear your shaping gear in to the store with you, all dusty, resin soaked and beaten. No-one will bat an eye…you’ll prolly even get a “contractor’s discount” Ha!


Well that pretty much nullifies my next question, which I’ll throw out there anyway.

Supposedly, EPS is not harmful to inhale when melted. However, if Gorilla Glue is Polyurathane, and PU is very harmful when melted, isn’t it dangerous to use when hotwiring boards?

GWN has removed that factor from the equation. Thanks :wink:

I glued up a 1 lb Lowes blank with Gorilla glue, had to use one and half bottles. It was okay, it took me a long time to get a good even coverage, and even then it still wasn’t great. After shaping the board, the hardest part for me was the rails, because I have weird ridges pretty much everywhere, and as a result, the rails are very boxy. And when foiling it I hit two glue lines, and they were almost impossible to shape. I had to switch to 40 grit sand paper and it took several hours just to get the lines themselves down to the rest of the board.

I am definitely switching to block foam after this, or Sfoam blanks. $14 for a blank is nice, but not if the end result has so many problems.

I’ve just shaped a blank glued up using PVA glue thinly spread. Hotwire goes through ok on the rocker cut if you take it pretty slow, 3 inches per minute seemed to be the fastest without getting stuck. I had already cut the planshape before glueing so I don’t know how that would cut, easier than the rocker cut I would have thought.

I glued the 1 inch sheets up to approximate rocker so no gluelines on the bottom, much better that way.

Seems to shape really nice using 40 grit, almost looks like a single block of foam except in a few places where I must have used a bit more glue.

I tried another blank using 3m photomount, but it didnt stick too well, and had to use most of a can for a single blank. The PVA covers quite well and is reasonably cheap so hopefully it’ll work better.


you can “bend-in” the rocker to your stringers the old way during glue up so you don’t have to hot wire it out…

a 32oz bottle gets me three blanks…

I only need to wire out the excess with my hotwire later…

seems like everyones using too much glue if they are having sanding issues…

and there’s always the elmers solution.

Anybody try this stuff?


3M™ Polystyrene Foam Insulation 78 Spray Adhesive Insulation 78 Spray Adhesive is a high solids, adjustable lace spray aerosol adhesive for bonding most types of insulation such as fiberglass, expanded polystyrene foam, and extruded polystyrene foam.

Been eyeing it up but like GWN said it’s probably too thin

as far as shaping the stuff…

nothing better than 36 grit belt sander paper cut and staple gunned to a 2’ long piece of 2x4… A great rail and flattening tool also 36 grit on a handheld drywall sander with 2" vacuum hose attachment makes a nice clean up tool and you can swap it out with finer grit dry wall screens to smooth out the burrs without doing a lawrence welk champange EPS number to mother earth.

what the hell are you making?

Hi Bernie -

When I picked up a 12 foot block at Home Depot they asked if I was making an airplane.

There isn’t any place to get block foam where you are, sr pato? I know it seems cheap, but once you buy the sheets of foam, and that very expensive PU glue, you might be better off getting a block. I just picked one up from our nearest EPS provider, and they charged me $25 for a 6" by 20" by up to 8’ (I had them cut it at 6’6"). Got two blanks out of it, and had a nice consistent density throughout, no chatters from hitting glue lines. Previously I’d gotten a 22"x24"x8’ from them for about $80, and got 6 blanks out of that. Either way, you can’t beat the price, and it is worth every penny (and the trouble to find a supplier) to avoid the headaches.

Hi Shwuz,

I wasn’t aware that we could order small blocks of EPS. I’ll look into that for future projects. For now I’m going to use a combo of Oneula & GWN’s advice since I still have a 2" sheet left.





'Neula…just don’t shave on Thursday and Friday; wear your shaping gear in to the store with you, all dusty, resin soaked and beaten. No-one will bat an eye…you’ll prolly even get a “contractor’s discount” Ha!


I really hate it when ever I walk into a surf shop or store like Fiberglass Hawaii or Woodcraft and they look at me in my Hawaiian Downtown Business Attire(i,e, Reyns, Kahala, Tommy Bahama $85 button down Aloha Shirts) and say… just got off work huh? Would even even weirder walking my pinstripe power suits. They might think I was from the IRS or FBI ready to shut them down or haul out their computers. Kind of like pulling up to the beach parking lot and having the “boys” ask me if I’m HPD before they light up for a pre-session toke on some pakalolo or batu… The short haired guy with a Kamehameha sticker in the back pulling up normally is an off duty cop, fireman, special agent or national guard.

Anyway back to the problem at hand…

Maybe Benny1 can illucidate as he’s the 1lb 2lb gorilla glue king here…

I haven’t had these problems using the stuff lately…

And john…

next time just tell them it’s for a mini-sub or nuclear weapon…

and then say… isn’t this that nuclear weapon foam I read about in the paper?

100% backin ya on that shwuz…

local EPS blower here will only do stuff like that for a 200$ minimum order.

and there’s the storage issue for me.

but yeah; no seams, your rockerbed is guaranteed perfect every time and super uniform density. Mebbe I should be asking about 6" blocks at Home Depot…

Ha ! So funny to see “$14” again & again…

Yep…glue ups are way easier when you bend in the rocker later, either with a stringer or in a bag when you put on a skin.

That GG pattern was nuts - never seen it soak in & set up so fast, and I’ve used it on over a dozen boards…dunno what that was all about.

I mist with a sprayer, it gets the right amount of moisture (very little) all around, but quick.