Any foamies built with wood sheathing?

[TheLastDeadMouse]

Hello all.

I've been considering building a teardrop trailer for a while now, but have been putting it off due to the cost of building “the teardrop of my dreams”. I'm a big fan of the very traditional wooden teardrops. I just stumbled across foamies the other day while looking for advise on how to glue together rigid foam for an unrelated project, and now I'm thinking that a foamie would be a great way to get a simple teardrop built relatively quickly and cheaply, then worry about making the perfect trailer some day down the road.

I like the look of wooden trailers better than the canvas and paint that most foamies use (no offense). I was wondering if I could use 1/8”x5'x5' 3 ply baltic birch ply or 3mm marine plywood and 2” rigid foam as homemade SIPs. It'd have the added benefit of having an already finished interior, and with some preplanning I could router electrical chases in the foam before gluing panels together and have them hidden by the plywood. I've seen a little talk about using foam and plywood as SIPs on this forum, but I haven't found any trailers that were actually built like this yet. Has anyone actually done this or are all the completed foamies up to this point canvas and paint?

For my design, I want to go with a very traditionally styled 4x8 or 5x8. For possible tow vehicles, I have a Chevy Volt, which is heavy and has plenty of torque, and a MG Midget, which has neither. 5x8 would be much more comfortable, but I'm worried it'd be too large for the MG to tow safely, so I'll have to decide which vehicle I'll use before I finish my design.

I drew up a little proof of concept drawing for myself before trying to tackle a full model and to run it by the folks here to make sure I'm not missing something critical. This represents a cross section view of where the side wall meets the roof. I drew the plywood as 1/4" in this drawing just to make it easier to see, but plan on using 1/8" to reduce weight. The idea being cut the inside plywood to shape, glue it to the foam then cut the foam with a hot wire or routers, using the inside ply as a guide but leaving it 1/8" higher. Then glue on the outside with plenty of extra. Put the walls up, then lay down the inside ply of the roof first, then laminate the roof foam followed by the exterior roof ply. Trim the outside ply of the walls with a flush trim bit, then cover the roof with another 1/8" of ply or a thin veneer. The whole outside would then be varnished or glassed.

Sorry for the wordy first post. Any advise or critique appreciated. Looking forward to learning more.

[josephhanson]

I built my second trailer using that concept. 1/4 ply on the interior, 2 in foam, the covered with canvas. It's sturdy and lightweight. I called it a "hybrid"
I too like the looks of the blond wood interiors.
Make it your own.
Good luck with your build
Joe

[GPW]

Yo’ mouse!!! No problem doing it that way , if You like it !!!

You know , you can get some really Great plywood (Aircraft plywood) at places like Aircraft Spruce Co. ( http://www.aircraftspruce.com/menus/wp/plywood.html 0 ... a bit pricy , but the Good stuff ...made for planes...

[KennethW]

check out this link
viewtopic.php?f=50&t=60697
I have not built this but here is my ideals.
viewtopic.php?f=21&t=59891

[KCStudly]

I'm using 5 mm marine Okoume for the wood appearance on the inside, and for the structural benefit.

What I found when trying to lay the ceiling panel across the walls (64 inches outside) was that the panel does not have enough strength by itself to span the walls w/o sagging. So given the choice of: (A) building a temporary support structure inside of the cabin or as a form to build the roof on, with the extra material and effort that would go to waste from it, or (B) adding roof spars every 8 inches or so and keeping the inside of the cabin clear during the glue up (so that I could get in there and clean up the squeeze out), I chose to add the spars.

On a similar note, when bending thin ply over radii, it will want to flatten out or bulge if not properly supported along the curve and given something to attach to, so plan on having ribs or spars at any arcs, or using a lot more material on temporary supports. (I built from the inside out as much as I could, so when I got to the roof on my build there really wasn't much more left to build; so it wasn't like I could plan on putting a significant amount of temporary materials back into the build.)

If you really want a SIP roof with no spars, I would plan ahead and either try temporarily spacing the walls at about 1/3 of your floor width (to reduce the span and sag) and building the roof on top of that, then place it on the walls later once they are in their proper locate; or plan on building a buck to build the roof over.

Another thing I found was that you really have to want to build light to make it worth the effort. By the time I figured out where all of my lights, cabinets, coat hooks, light switches, etc., etc. were going, the number of pieces of blocking that had to be routed and glued into the foam became quite a large number, and involved a substantial amount of time consuming effort to install piecemeal. Let's just say that about half way through that process I swore I would either use skeleton ply or traditional framing if I were to do it again.

With skins on both sides you won't have to fuss so much to keep the foam free of dings and flaws, but don't underestimate what you will need for rigid connections.

Your results will surely be different, especially if you keep things very simple, but to give you an idea, here is a model of my hybrid build with the plywood stripped away. When you get down to the details there are a lot of hard points needed. At least that's how mine is turning out. (Note that the extra roof spars and front radius mini ribs ("riblets") aren't shown here.)

[GPW]

Interesting what Aircraft Spruce has to say about Okoume ...
“ Okoume ( o-KUE-me), also known as Gaboon, is an African hardwood widely used in Europe over the past century. Light pinkish brown in color, sometimes lustrous with variable interlocking grain, the rotary cut panel can be painted or finished bright. The natural durability of this species is extremely low and care must be taken to finish all surfaces, face and edges. Often recommended for use with epoxy saturation systems "

[KCStudly]

Polyurethane toughens it up just fine.

It can get scuffs in the face if you are not careful handling it or if foreign stuff gets between the sheets. I'm sure other species have the same problem to some degree, but I can't really comment on those.

It was my understanding that it is commonly grown in the Philippines, and has been referred to as "Philippine Mahogany".

I have no complaints with it.

[mezmo]

If I was doing "Mini" SIPS, I'd use a perimeter frame around
all the panels and openings therein. Just for ease of joining and
installation of components. [Add necessary hard points too.] The
canvas and glue and paint skinning is a continuous, non-interrupted,
membrane running over all edges. Gluing the edges of the 1/8
inch plywood and the foam together would not be as strong a
joining as a wrapping or covering the joint with canvas and glue-paint.
The glued foam joint may not itself fail, but from what I've seen on here
the foam usually does fail right after the glue line. And a 1/8 inch
plywood edge glued to another 1/8 inch plywood edge has minimal
surface area for the gluing of each panel to the others. You don't
mention any other joint/joining reinforcement on the edges, say
e.g. with fiberglass fabric and epoxy etc..

This build;
Curved Structural Insulated Panel Build.
viewtopic.php?f=50&t=60697#p1090202
His own Blog:
http://hipstercamping.blogspot.ca/
Is really interesting, but the builder uses the technique(s) he uses in
his day-to-day work, utilizing some specialized equipment. A "Mini"
SIP with perimeter framing should be more doable without that
specialized equipment being necessary. He also BTW, covered the exterior
with canvas and TBII and paint as both a covering and a joining reinforcement.

Linuxmanxxx, a member on here, has the most experience with the
"Mini" Sips. Here is a link to all his posts. It will be somewhat disjointed
as they are not a continuous narrative on them [It has all his posts on all the
topics he has ever posted on.] but you should be able to garner his techniques
from those on the topic and from them discover his threads that are more
involved with the topic. This should be a little easier than trying to use the
"search" feature on the forum here - from my experience with that.
search.php?author_id=11546&sr=posts

Cheers,
Norm/mezmo

[GPW]

You know , with all the talk of the Foam failing , we’ve yet to hear of a failure in the real life application of Foamie campers... We can test everything to destruction , but it doesn’t mean we’re going to experience that in reality .... or that anything else would do better under the same circumstances...

Foam with plywood , then canvas over that .... That’s just Gotta’ be STRONG eh ??? I really think (JMHO) that chipboard in the same thickness would do as well or better than the plywood , easier to work , and cheaper... just throwing a little Gasoline on the BBQ...