Teardrops n Tiny Travel Trailers

How do you join multiple panels together structurally? Butt Joints, rabbets, tongue and groove, "continuous biscuit". Looking to build a 6' x 10' x 2" wall. What types have been used? Any strength tests been done?

For joining walls?


For joining corners?

The thing to remember with foam is that the foam is relatively weak. Even a well executed butt joint will fail just past the joint. That said, I like the slot with a long wood joiner because it aligns the edges along the joint. I have a router bit the will cut a 3/4" deep, 1/4" wide slot. I pair that with a 1" wide 1/4" wood joiner strip so there is some room for gorilla glue expansion. That's important to keep the foaming glue from pushing the joint apart. I use the minimum amount of glue and round the edges of the joiner strip so I don't break off pieces of foam while inserting the strip (keeping the joint from closing.)

Avoiding glue squeeze out on the surface of the panels is important because it's easier to sand the seam flush if there is no glue to worry about.

Let's not forget the Les Nessman effect on the strength of those joints

I have used the wood joiner before, but I like the idea of using foam instead. Expansion and contraction would be the same. I glue out to the edge and then take a Dremel with a small grinding tip and grind the glue line below the sanding line before I sand. This makes the sanding easier and then you just need to fill the small slot with filler before canvasing.

[quote="ghcoe"]I have used the wood joiner before, but I like the idea of using foam instead.[quote]

By foam do you mean spray foam? And would you just do this on a butt joint?

Thanks, Bill

I use a glued butt joint with sheetrock fiberglass joint tape glued on both sides. Toothpicks or kabob skewers make good inlinement tools.

stcyrwm wrote:

ghcoe wrote:I have used the wood joiner before, but I like the idea of using foam instead.

By foam do you mean spray foam? And would you just do this on a butt joint?

Thanks, Bill

Like number 4 on top. I think it would work good to join foam panels. Like I said expansion and contraction rates would be the same. Wood expands/contracts slower and less than foam does and can telegraph patterns through the canvas and/or foam.

We’ve ever just used Butt joins to glue the Foam , and maybe the thing to consider is the skin (s) and any other structure as a whole unit ( unibody) … using every part to strengthen the join to other parts … We’ve even thought about using wood and thin plywood as part of the structure for critical areas such as floor to wall join (see drawing)
But then the butt-joined simple Foamie we made at first lasted just fine …and got towed across country when Bonnie got it … and then she had to fight to cut the floor wall joins for her modifications … that was just foam /thin Linen canvas and used bedsheets inside …
Sometimes we tend to overthink the possibilities , which can only lead to overbuilding , which is really never a bad thing eh ...


Ps. I can even see in the drawing ^ that a notch ( Dado ? ) in the foam wall - floor attachment would make assembly easier and still use the extra gluing area of the sheeting … a simple hot wire tool makes notching pretty easy and accurate ( stinky , but less messy than a saw notch ... )

Cut finger joints into all the foam boards. They fit snugly, and the spraycan foam works great for adhesive on these joints.
At the time I did not have my multi tool & Hackzal purchased yet, so I hand cut each finger/slot using a hacksaw blade (Just the blade, not attached to the saw handle/frame..seemed easier to control)
Have a vacuum tube next to the cut area if the foam bits bother you.

Don't over complicate foam to foam gluing. It just takes longer to build that way. The strength comes from the skins and any added framework... but mostly from the skins.

General guidelines???

Do I want to always glue foam to foam, or can I glue covered foam to foam or covered foam?

Do I want both sides covered before I Glue walls to floor, to roof, etc?

If I plan to use the foam cut from an opening to make the door, do I want it all covered before I cut, then add covering, or should I always cut out then cover?

Come to think of it, should I wash that drop cloth canvas before gluing, so any shrinkage will have already happened, or will gluing fresh canvas and having a little shrinkage add to the strength?

I’m thinking all 2” foam, a 5x10x4 shell, two doors and a rear hatch. I have discovered that manufactured doors are EXPENSIVE.

Might build in a shelf, partition or ceiling arch, to add stiffness.

HF, if you wet a piece of canvas , the fibers swell with absorbed water and the fabric appears to be Larger … when dry it shrinks …. There is always some interaction on natural fibers , so shrinking is a normal occurrence … We don’t worry about shrinking , we just leave a little extra length on the ends , so we can trim it exact after it stops shrinking , but before it dries completely …And then when you paint it , the paint shrinks too ( loses water ) taking canvas with it …
And for doors , we cut out the foam , then cover it … Worked great in the past , no reason to buy overpriced tiny doors …

I framed my door and opening with wood so I'd have something solid to attach the hinges and latch. Making your own doors gives you the freedom to use whatever size and shape you want.

In general seems the norm is finish assembly and gluing, fabric/paint skinning is the last step.

An exception would be removable panels, so skinned to skinned,

caulked with a (also removable) sealant if needed, but that's just me thinking.

Can't imagine needing to do raw foam attached to skinned, but also don't see why it couldn't be made to work.

Beauty of Gripper is, the stuff can be made to stick to "just about anything" but the usual low-energy slippery plastics.

Thanks. That all makes sense.
Grab the Gorilla glue and your favorite cutting and measuring tools, then build what you want.
Then skin it.
Then paint it.
A little finish work, and you're camping.