Crazy idea? Keying XPS foam with laminate with 5200 or similar? Someone tried it?

Hey, thinking out of the box here. Maybe someone has given it a try.

We have a XPS foam shape which we would like to laminate over with epoxy & biaxial glass.
As XPS is closed cell I know that laminates glued to it can peel off, especially if its a hand lay up without vaccuum.
Now here comes a bit of an unconventional idea. Maybe someone has tried it?

How about using 5200 or something similar to stick the first layer of glass onto the 36grit sanded XPS foam and then laminating onto that "dry" glass layer from the outside.

The total glass layer is 5-8mm thick and the foam is primarely a former for a fairing. The foam is completly encapsulated and can not go anywhere.
Could that work better than laminating straight onto the XPS foam?
I KNOW that is unvconventional thinking, but I wonder if it COULD work.

Especially knowing that 5200 sticks like hell to all sorts of materials. Thoughts ideas?

Thanks!

Btw. What is 5200 exactly from a chemical standpoint? Are there similar formulations used on an industrial scales which do not carry a premium "marine" price tag? Brand names? Recommendations?
As the stuff is not exposed to sunlight at all we could perhaps use a cheaper alternative?
How about this: https://samaro.fr/pdf/FT/HBFULLER_FT_ICEMA_R145-45___FR_.pdf

 

1. Welcome.
2. You would be just as well off to laminate glass directly to foam substrate. You get no better adhesion with 5200 with more expense.
3. Loctite polyurethane concrete patch has worked well for me in similar fashion to 5200.

4. I am an amateur.

 

Yes, it has been done, and no, you don't want to do it unless some special circumstances forced you, like laminating over wet wood.

Just rough up the XPS with 80 grit, they build surfboards this way. If the foam is just a former you are not concerned with adhesion anyway, and could even remove the foam afterwards (drill hole, pour acetone, watch foam dissapear, close hole).
Anyway, fiberglass delaminates from XPS because the foam has such a low shear strenght, not because epoxy does not adhere properly to it. Sanding with rough paper or poking millions of holes into it with a roller increases the surface area of the bond, but does not solve the shear problem, just mitigates it.

5200 is a polyurethane adhesive sealer that remains flexible after curing. There are hundreds of similar products, all with more or less adhesion and/or flexibility.

 

Maybe expanded polystyrene (EPS) will work. Have a sample 1" pc 6" x 4" with .010" aluminum on both sides that is used as an exterior cladding/facade.
It seems to have bonded very well. Would like to know what glue was used but think polyurethane or epoxy would work very good

 

As mentioned, bonding to XPS isn't the problem, the low strength of the XPS is where the failure starts.

Don't over complicate the project by solving problems that don't exist.

 

Not sure what your application is but Rob Denney is experimenting with "top hat stringers" for building his 80' cargo ferry proa with solid core fiberglass and a kind of "truss network" of stringers formed with XPS. He's using something like 1800gsm fiberglass for the bottom of the boat. It seems to work well for fine narrow displacement hulls. Check out this thread, some interesting comparison, or his build log.

So yeah it seems to work if you design it so it is stiff enough. And you would just use epoxy and ideally vacuum infusion on a flat table.

You could also "score" the XPS foam in a grid pattern which increases adhesion and serves as flow channels - if you would want to vacuum infuse a fully insulated panel. But then the whole thing gets heavier and more expensive again. Epoxy or adhesives are expensive per m². Like others say the problem is the inter-foam strength but there is also higher density XPS. But that denser foam then also gets more expensive compared to real foam.

The laminate for box trucks is also just 1-2mm fiberglass on XPS but of course they don't see the loads a ship hull does.

 

The 5200 is honestly, a horrible idea. It doesn't change the weak shear character of lower density xps, it cures really slow, and it would be difficult to glass over as it won't lay down smooth or sand easily.

So, don't.

lotsa good points from other members; I prefer to abrade the xps with 36 grit floor sanding paper which gives it deeper key and expands the surface area which technically helps a wee bit, but not much

I tried to bond to foamular 150 xps no key and found it was dreadfully weak and easy to shear. The 4'x2' test didn't even have the shear strength for the peelply, but peelply is a good test..

 

Have heard of xps adhesion problems (peel strength) therefore reason for mentioning eps which seems to have good bonding characteristics therefore solve high concern of maintaining foam core build structural integrity.
This form of build using exp or eps would b limited to smaller boats (guess upto 30') as that is what present day knowledge limits are, composite would be varying thickness of foam core but would definitely use ply sheathing 4-6mm both sides (much greater shear strength) finished w a light fiberglass layer rather than trying to achieve shear strength with an all fiberglass membranes.

Few years ago had to remove a few hundred SF of 2 " blueboard (xps) which became completely waterlogged and extremely heavy even in small chunks after a few years sitting indoors under commercial refrigeration units , hence the hesitancy using xps in a marine environment especially if boat is sitting on water full time or even having small pools inside hull were it would collect and eventually penetrate the sheathing, it seems to wick so whole piece becomes wet. Never saw eps become waterlogged

 

I've heard of something similar with XPS vs EPS for insulation against earth but it doesn't make sense to me. I think the argument is that EPS is porous so it can dry out again. Water gets in, but water can evaporate. While XPS is closed cell so... ? Not sure how closed cell would soak up water unless it's being subjected to forces that make it crumble. Maybe with repeated freeze / thaw cycles? I've heard that PU foam is especially friable under repeated stress.

In any case if it's a stringer that is enclosed in epoxy like plywood would need to be it should fine. Unless you drill into it.

 

This is a sample of the very rigid eps composite previously mentioned, it does have 3MM polypropylene layers between aluminum n eps.

Would bet that a test submerging eps n xps for a certain period would conclude the xps gaining drastically more water weight

 

Epoxy encapsulation should prevent excessive water intrusion but what happens when not, does the water remain inside indefinitely or almost so considering very little room for escape, then also factoring the adhesion problem makes for a poor choice vs. EPS

 

eps is porous, but it can never dry out under practical circumstances; the real world example are hot tub covers; they eventually get saturated, but I put a set in a 90 degree room for two weeks with fans and they only lost like 2 pounds of say 20 pounds water each..what happens is the water gets in over a long period of time and the drying happens on a nearly molecular level as the foam tends to protect the water from evaporation...above the hot tub the foam was heated to 100F and it probably would have dried a bit better at 110F, but it became a lost cause quickly

 

But what physical process would explain that? Diffusion? The same should apply to EPS. Closed cell XPS foam vs porous EPS should be no contest.

 

Fall guy, your description of eps water gain sounds exactly like what happened w the xps and I wonder which one gains faster but considering the cheap eps picnic coolers that almost never happens w them so maybe its high heat which caused it in that case

 

No, they are thin enough to dry out in someone's garage before they break or fly into a lake.

xps water gain is slower, but this thread, for me, has run it's course