XPS glue up warning

Hi All,

I haven’t seen a lot of discussion about glue types for XPS when gluing sheets together.  I did see that some people had success with titebond III (the waterproof one), and mixed feelings on gorilla glue because the PU in it may melt the foam and/or expand.  I see that great stuff works well, and epoxy or epoxy w/ microballoons too.  I can say that I found out this week that using an air drying glue(titebond) with XPS is a huge mistake - unlike EPS, XPS is totally closed cell, there is no air exposure at all, it never dries.  NOTE: this only applies to foam to foam joints.  I imagine a foam to wood stringer joint would still cure properly.

Background: I built a rocker table and was gluing up 2 sheets of 2" GreenGuard/Pactiv 2# XPS (green).  Spread a thin layer of Titebond III on both surfaces and pressed on the rocker table.  24 hours later removed weights and both sheets delaminated, the glue was still wet everywhere except the very edges.  Shrugged, added weights back on, drilled a couple hundred very small holes through foam for circulation (I was contemplating the holes per surfer steve anti-delam recommendation anyway) and let it sit for a week on the rocker table.  Took the weights off today and was hopeful at first, but the sheets delaminated as soon as I flexed the block.

Lesson learned the hard way.

I ordered 2 gallons of epoxy for glassing last week, should be here tomorrow.  I also thought about using GreatStuff, but without a stringer, I figure the epoxy should help keep it from being too floppy until I can get some glass on it.  Unless someone has a better suggestion, I’ll be using epoxy and will try to keep it about 1" from the outline for easy shaping.

This did get me thinking though about the delam issues with xps.  If great stuff forms such a good bond to XPS, what about putting a skim coat of great stuff on a shaped board, sanding out the bumps, to leave a thin fuzzy layer of polyurethane, then glassing?  Do you all think the epoxy would get a better bond?  Better shear strength when dented?  I might try it with some scraps.  Even if it does work well, it might still be difficult/impossible to do evenly on a whole board.

Yes indeed XPS is closed cell foam.

Surface bond only.

Gorilla Glue will work fine.

Work fast.

Can un-clamp in 30 min.

Shape it in a couple hours.

Glass only with Epoxy.

Sealing with glue has been tried since the 50’s.

Don’t use epoxy to glue the foam pieces together, you will have a hard time shaping the blank. I use gorilla glue, but I’ve also used a spray glue that is blue. I prefer gluing up rocker slices, but I have 3" or thicker foam, so there’s fewer slices.

sumo pu , roo glue or xps cement

gorilla works fine but sumo dries white/clear and doesn’t stain your hands as bad

also increase the two surface areas by fluffing them with 40grit sandpaper or a meat tenderizer roller before gluing or glassing

its a surface mechanical bond so the more surface area between the two components the bettter the adhesion

kind of like XTR or Bufo’s 3D glassing

elmers/titebond only works well with big bead superlight EPS and of course wood to wood

there’s a marine sealant bonding agent that wood boat/board builders use

just got to watch the solvent content or what ever you use

Thanks for the info on the various glues for XPS.

I too learnt the hard way that wood glues that work for EPS don’t set between sheets of XPS. I don’t feel so bad seeing a guru like oneula did it too :slight_smile:






Can you tell us what type of cement you mean?

I don’t know how you get this as the company is in Ontario Canada


Here’s another that I’ve used with some success



Thanks Oneula.  How well do they sand?

Have your tried the 3M Polystyrene Foam Adhesive 78?  If so, how well did it perform/compare with these other adhesives you posted?

3M™ Polystyrene Foam Insulation 78 Inverted Spray Adhesive


3M(TM) Polystyrene Foam Insulation 78 Spray Adhesive Inverted

I wasn’r able to get that 3M stuff but that’s what Resinhead recommends as Mr 3M .

I did get a cans of the demand products and this stuff from hotwirefoamfactory

the demand stuff wasn’t too bad but the hotwirefoamfactory spray didn’t hold up

What I do is use the spray to add on the rails to my homemade blanks

which are composed of a 1" sheet of blue dow foam from FBH and a 2" sheet of cheap insulfoam from Home Depot

These two sheets are bent against a rocker table (sample board) in a bag over night with a woven bamboo springer inserted between the two sheets of foam

we usually plane/sand down one side to create an area the “springer” to sit in and then rough up both sheets before applying PU glue  or epoxy to bond the EPS to the XPS bottom. The PU glued blanks come out really light compared to the epoxied ones and I’ve only tried roo glue once but Charlie has used it beofre in gluing up his EPS blanks.

For PU I prefer sumo but I can’t find it anymore in the larger bottles.

I have doubts about the flex charateristics of hardened PU which is none and means a breakdown and delam over time

When I had the spray stuff I used to use it to bond 1/8" balsa/paulownia/cedar perimeter stringers to my blanks after cutting out the outline narrower than needed because this allows me to not have to apply the bottom skin to hold the rocker while I bag the two sheets of foam togethor.

Once I slap on the wood perimeter stringer I than attach 1" of either blue dow XPS foam or 6’lb Precision foam (poor mans corecell) for rails

The blue dow bottoms give the board some extra twang while the blue dow rails prevent water penetration from rail dings and shape better.than EPS

Once shaped we then usually cover the entire shaped blank with 1/16"-1/8" balsa and reshape the rails via light sanding before glassing

Sometimes we use the woven bamboo wall covering for bottom skins or as a deck patch or skin stringer like you see others do now with those carbon fiber strip stringers.Charlie has been using Obeche in the bottom tail area for a similar purpose as well as angled wood strip to increase flex where needed.

Woven Bamboo has always been my version of carbon fiber, although I have recently acquired some of the net stuff as well as woven carbon tape for rail support.

Sometimes we’ll lay a strip of exotic wood like wiliwili/mango/down the center of one of the wood skins for decoration but the multi densities between them and the softer balsa  create a sanding problem. Also bending the wooden deck skins around the rail without breaking is an art that only Charlie has really mastered. It all about using the right strips of balsa for the right position and appropriate the use of green tape, lots of it.

Now we are experimenting with cork as a deck skin because its just easier to use than 4"x48" strips of taped up balsa. A single skin that takes any shape you need.

it’s all way too much work than just buying a blank and going at it with a planer.

But what’s the challenge in that other than learning to shape?

but its a learning experience none the less

and the end products are just as useful as anything you can buy off the shelf and they look better two.

mostly just for personal use or charity fund raisers

plus I get to spend time hanging out , arguing and cleaning up after my brother

the real shaper/glasser of the family

I’m just the idea-financier-cleanup boy of our crazy adventures



You have come up with some interesting technology Oneula.

I agree with you.  The fun is in the experimentation…

I’ve gone as far as 3"thick pink, hot wire the foil in, and glued up the seven strips with RR epoxy…  the lines, as pointed out, in that orientation, are not that big of a deal.  On the down side, the first time around I learned three inches of xps cut at the same speed as 11 inches of 2# eps…   Ha!  One small delam in experimentation… It’s back on the frankinboard racks…