Which glue for XPS to plywood?

[Finlander]

Hi all! Thanks for a great forum. I have been reading upp on things for maybe a year now on foamies and I am in the middle of a hybrid sort of squaredrop build myself. My first buld. Currently it is really just the trailer and the floor done and now I'm planning how to build the walls and roof. Which leads me to my question. What glue would be suited for glueing larger panels of XPS to plywood? I want to avoid anything that will not cure and stay wet in the middle of a larger panel.

I live in cold humid area (Finland), so I would like to seal or treat all wood surfaces, also the plywood surface that goes against the XPS. So I'm thinking could i use TB2 as it would seal and bond, but will it dry also in the middle of e.g. a 50"x30" panel? Or should i treat the plywood surface first and then use some other glue for attaching the XPS?

I will use thin birch plywood as the external skin and pmf it with old beadsheets from a hospital.

BR
/KT

[linuxmanxxx]

3m 30dnf water based contact cement it's tacky when you bond the 2 surfaces. A lot of the polyurethane glue need moisture to set and don't like cooler temps.
Steve

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[Terra6]

Depending on the size of your walls, adding mechanical attachment in addition to glue could be an option due to the question of glue adhesion effectiveness/longevitu in low temperatures and high variations.
A sheetmetal U Channel or screwed down L backer board/ plate would add extra set to the edges if concerned about glue only and would double the bonding. Some have used dowels inset to floor and walls is another option.
Imho, would want a solid backing to bind and reinforce.
But on a small 4x8, probably not as critical if that is the size you're building.
A thought to assist...

[Pmullen503]

[quote="Finlander".......... What glue would be suited for glueing larger panels of XPS to plywood? I want to avoid anything that will not cure and stay wet in the middle of a larger panel.

BR
/KT[/quote]

I don't know what is available in Finland but moisture cured polyurethane glues like "Gorilla Glue" (brown formula) is a good option. Spread it thinly, mist with water and join your panels. Find a formulation with enough open time and not too vigorous foaming action. Make sure you figure out how you are going to clamp the pieces together while the glue sets. I really holds up outdoors in subzero temperatures.

[Finlander]

Thanks for the input! We have gorilla glue (the brown stuff). Another option I was thinking about is using some sort of construction glue like sikaflex, that I could spread thinly with a plastic scraper on the complete surface where XPS would be attached, but I always run into the concern will it dry also in the middle or stay moist and ruin the plywood. I remember reading here or seeing a clip on youtube about a guy experimenting, and some glues didn't dry in the middle, but I just can't seem to find that now to watch it again.

The idea was to build the walls in a horizontal plane before attaching them to the floor of the trailer, so I can just use weights to clamp the glued XPS pieces to the plywood outer skin of 6,5mm birch plywood. Also some stick framing (pine) will be added around the edges of the walls, so the camper's outer shell of plywood will be held together wood to wood, TB2 and nailgun. This means that I don't have to rely on the glued XPS to actually hold the camper together, but it should help make the walls rigid together with the simple stick framing, as the 6,5mm plywood alone is quite flimsy. There will also be wood framing around windows, door and bulkhead. So the panels won't be very large. We don't have 4x8 sheets of XPS, only 2x8.

Btw, the XPS in the walls will be either 30mm or 40mm thick.

/KT

[pchast]

Test the construction glue you pick. Several of them will melt the foam.................

[Finlander]

Only have simple plans on paper, as this project was supposed to get me away from the computer and reliev stress. But here I am, loosing sleep with construction ideas flying around my head and brain solving problems while my family is still sleeping on a Sat morning.

[linuxmanxxx]

The water based contact cement I was talking about is light green. You coat both surfaces with a thin coat and when it's dark green the water has evaporated and you align and press the 2 together and it won't hurt the foam or expand just stick. Fast easy and the least messy of anything mentioned. I've used the expanding water curing polyurethane like gorilla and it's hard to manage the foaming and swelling as well as extremely messy. It costs more but lowers build time and stress levels a lot.
Steve

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[Finlander]

The water based contact cement I was talking about is light green. You coat both surfaces with a thin coat and when it's dark green the water has evaporated and you align and press the 2 together and it won't hurt the foam or expand just stick. Fast easy and the least messy of anything mentioned. I've used the expanding water curing polyurethane like gorilla and it's hard to manage the foaming and swelling as well as extremely messy. It costs more but lowers build time and stress levels a lot.
Steve

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That sounds as a really good option! Managed to find 3M 30NF (not DNF) which according to the description would suit this need, but only wholesale for industry. No resellers by googleing. There is a shop nearby selling paint etc. for industry, need to pay them a visit to see if they can help. But I'm not counting on being able to buy this 3M 30NF so need to keep exploring other options.

/KT

[linuxmanxxx]

Amazon has it uline has it grainger not sure what you have available. Google shows desertcart has it in Australia.

I did aluminum outside and paneling inside used a couple gallons.
Steve

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[MtnDon]

The 3M Fastbond 30NF is great stuff. There are two versions, light green that dries to clear/white when ready to use and a white that dries white/clear. Same cement but the green color is a handy indicator. It is not flammable or explosive when wet like most of the other contact cement. I have used it for foam to wood, carpet to wood and carpet to foam as well as plastics to wood and wood to wood. Positioning is critical or if the oversize sheets are glued first and then trimmed later.

Can be applied with a brush or a roller.

There are a number of products that are meant for commercial use but here in the US an individual may find and be able to buy them. Other countries may have more strict regulations which can be good and bad. Well worth looking for. I have bought it from Zoro.com here in the US.

[MtnDon]

An electronics company I buy from also sells the 3M fastbond 30NF. They have outlets in Europe. The name is Digi-Key

[whiteryanc]

Following, super interested to see what you come up with here. I'm just starting conceptualizing a square drop and my mind has gone to a hybrid foamie/traditional build for weight and hopefully simplicity. Did you consider any other exterior material than plywood?

[ghcoe]

Is there a reason you want wood in your build. Is it your preference or do you feel you need the wood to make it strong? You can do away with most, if not all, your wood structure shown in your drawing above. You just have to have faith that the foam and canvas is plenty strong by itself.

My builds use wood in the floor, 1/4" wood inserts around the door and 1"x3" lumber for shelf facings. There are a few places I use roof flashing. The rest of the build is all foam and canvas.

Something to consider is that XPS foam contracts and expands faster than wood and the less you wood you use the less problems you will have. I have been beating on this trailer in the back country for a few years now . No problems at all so far. You can check out the channel for other trips I have taken the trailer on.

Good luck! George.

[Finlander]

Hi George,

I have watched all your videos, great informative stuff.

Actually I spent quite a long time planning and trying to make up my mind about going full foamie, woodie or hybrid. I'm confident foamies are durable enough for my usage, but as this was supposed to be a fun project for me and i like working with wood so this hybrid felt like the best option to me. This also gives me the benefit of getting to experiment with new stuff (XPS, PMF etc.) on this being my first build. I have a feeling this will be my learning project that will maybe someday be followed by a little bit bigger and fancier build.

And I found a suitable glue in my local harwarestore, a water based contact cement. It held up really nicely in my tests.

/KT