Attaching Foam

[Dirke]

Hello again,

So I am still toying with the idea of a foamie, mostly because of the weight savings. I had an idea about attaching the foam to the trailer. I thought it might work well to use some sort of hard tubing (like PVC) to keep the screws from crushing the foam. Cut the tubing the width of the foam, drill a hole in the foam, insert tube, squirt in some silicone, then put the screw through with a washer on the outside to keep the foam from ripping off the screw. My plan would be to build the kitchen divider and cabinets at the front with wood first, then attach the sides. I figured it would put less stress on the spars. I am toying with the idea of a hybrid, foam sides, wood top and thought this might help strengthen everything.

Thoughts?

Dirk

[eaglesdare]

my personal opinion only here: i think that perhaps what you are suggesting is overkill. lol seriously, i used gorilla glue to hold foam down to wood floor. that's it. still solid today. about 3 yrs now. of course it is wrapped in canvas, and the canvas is attached underneath the wood also. but if there was any wiggle you would feel it. like i said, still solid.

[KCStudly]

Gorilla Glue alone is fine. It is as strong or stronger than the EXP foam panels and grips to wood like mad; even cedar with its high resin content.

Most foamies do have a plywood or “torsion panel” type floor to glue the walls to, and to wrap the canvas under, and this is what typically gets screwed or bolted to the trailer frame from underneath, usually pinching the canvas that is wrapped under in between the frame and floor for added security (even though the canvas is fully glued).

You want to spread the loads and forces out over as wide an area as you can so that every part helps contribute strength to every other part. The glue joint does this very well; whereas mechanical fasteners tend to concentrate the loads. My thinking is that the PVC anchor method that you have suggested would actually create a weak point where your wall could tend to fail or be crushed internally.

Eliminating metal fasteners in your wood to wood joints (either by using only glue, using biscuit/plate joinery or dowels, or removing screws and staples that were only needed to align and hold glue joints tight during cure) is another way to reduce some weight. Maybe a little extreme, but… how light do you want or need to go?

Keep reading the posts, you are catching on quickly.

It seems that one of the biggest mistakes first timers make is to overbuild every part and end up with a heavy tank of a TD. Think airplane not tank. The strength is in the cabin as a whole unit together, one big beam from front to rear, and all of the little attachments where you add cabinets and bulkheads and spars add to the whole. Unless you are building a monster RV, use smaller, lighter pieces, but make sure to fit your joints well for good glue bonds.

And, oh yeah, welcome to the foamie side of things!

[Dirke]

Awesome. That is very helpful. My goal is to make things very light so, no matter what vehicle we own, we will be able to tow it and it won't cost us a bundle in gas. So here I am looking at foamies. I have a basic idea of what I want. Now I am just learning as much as I can before I start. Don't even have a trailer yet but that will come.

I wondered about the stress points. That makes sense. Using glue and the method you are describing sounds cheaper and easier anyway. As far as the torsion panel goes, do you put that under the trailer or does it go inside? Do you put the canvas on first before you attach the wall?

[KCStudly]

Some people just use a simple plywood floor, glue the walls and bulkhead to that (sitting on top), top it with a ceiling and wrap it up. In most cases it is recommended to first apply strips of canvas running along the wall to ceiling seams, and reinforcing the wall to floor joint (if doing a pure foamie, you could even add these extra strips to the inside corners at the bulkhead/wall/floor/ceiling joints). Then, usually due to the available widths of canvas, the sides are covered in one go wrapping over the ceiling a little bit and under the floor at least a few inches (4 or 6 or so). Then the roof is done wrapping over the sides a bit. This way you get double or triple strength at the seams.

Some people build out over the wheels, so they may be able to do the wrap after they have mounted the cabin onto the trailer (depending on how much their wood overhangs their steel). Some people like to apply the canvas in the flat, so they leave extra material (unglued/unpainted) hanging off so that it can be wrapped and glued to the adjoining parts later, or they just add reinforcing strips on top after. But you have to be careful because applying canvas to just one side of a flat panel can cause it to warp when the canvas shrinks. Pre-shrinking the canvas may help(?). Applying the inner and outer skins at the same time is another method to help prevent warping. (These are some of the issues that drove me to the hybrid method using thin interior ply skins; hopfully stabilizing my walls and giving me options for the building sequence.)

Some people put foam under their single layer ply floor (usually in between a subframe of wood, not usually done on foamies), some put foam on top of their ply floors (one of Bob Henry's builds comes to mind, and maybe Eagle's Mickey TD), some sandwich their foam between thin layers of ply (usually with a perimeter frame of wood, like mine). Some use thicker ply.

Just like all of the traditional TD building methods, there is not one correct way. You have to do your homework, decide what will work for you and your design goals (cost, method, end use, size, available trailer, available tools, available building/shop space, available time and $$$, etc.), and if still unsure, test.

Dig in. There is so much to learn here, and not just in the foamie section. I lurked for 2 years while reading everything, working on my design, and never even posted a thing... until I knew that I was committed to the build (and now I should just be committed! )

First and foremost, make sure you understand what you are getting into. If your goal is to throw yourself into a big project and the journey is half of the destination, have at it. If you are really just looking for the cheapest and fastest way to go camping and just want to be off of the ground, then maybe you should think twice about buying a used camper. These are two extremes and it sounds to me like your thoughts are somewhere in the middle. My advice is to study up and do some realality checks before you decide which way to go.

If you do decide to take the plunge (...even if you don't), you will get a lot of help from the great people on this forum, especially if you post lots of pictures of your build. We like the pic's.

[Dirke]

Ok, that is helpful too. I am pretty positive I am going to go this route. I am a teacher and have the summer off to work on this kind of thing. What you said about the floor brings something to mind. I saw some thin rolls of insulation with a foil lining on the outside. Would it be fusible to use just one layer of ply like you suggest and then put down the thinner foil covered insulation and then add your flooring on top of that? My sister has some leftover laminate flooring she wants to give me. Probably would add more weight than I want but the word free always makes me weak. I live in Michigan and it gets cold sometimes. Of course if you have a mattress you don't really need insulation underneath you.

[KCStudly]

Of course if you have a mattress you don't really need insulation underneath you.

That's a whole 'nuther long winded debate that has been battled about elsewhere in the forums. My wife gets cold and has pour circulation. I'm putting 1-1/2 inches of insulation all around TPCE and at this point I have no plans to camp in cold weather, but it might get chilly overnight at high elevations, so...

Re: types of foam and thickness. Wait for it, here comes the thicker is stronger mantra... Since the foam is so much lighter than any other thing that you will be building your trailer out of, and because the strength comes from the inner and outer skins, and because the further apart the skins are (moment of inertia) the stronger your structural member will be (exponentially), the thicker the foam the better (to a point where the strength properties required have been achieved).

TPCE is 5 ft wide. TPCE will be carrying some heavy stuff (water, batteries, CI, lead, griddle, etc.). TPCE will go off road onto some fairly rough forest service roads. TPCE will have a full perimeter welded frame, fairly thick panels and interior plywood skins.

See what I mean about deciding what your needs are? I'm building light because I want to carry more heavy stuff, but I am also building strong because I need reliability 100 miles from the next humans.

How big will your camper be? Big tall walls with lots of highway miles and open plane wind speeds, or short and narrow? Thicker foam gives greater strength and insulation with very little weight penalty.

[Dirke]

I would like to make it 4 ft high and 5 ft wide. I am not sure how long I want to make it yet. I would like plenty of leg room while I sleep and perhaps room for a low bunk for the little rug rat. I was planing on using 2" foam for the walls (still debating on the roof). I'm curious if I could make the floor one ply then lay 2" on top with the laminate flooring over that. It would allow me to glue the bottom foam to the walls and have plenty of R value without having to add the weight of a subfloor frame. I imagine you would need to leave some space for expansion?

I will have to wait until I have some scrap foam to see if it would support the weight that way. I don't think they would like me standing on the foam at the local lumber store.

[ghcoe]

Just keep in mind that heat travels up. You should not need as much insulation in the floor as you have in the sides and top.

[KCStudly]

True, what ghcoe said, but there is also something to be said for consolidation and material yield in your cut schedule.

The deciding factors for me were strength, insulation, and consolidation. By using thicker foam in my floor I felt that I could space fewer subfloor xmbrs further apart because they were deeper and stronger.

Remember that everything you add above the wall sill is stealing away your head room. 4 ft is plenty of head room, but I have concerns that my wife might be uncomfortable in such a small space, so this is just one of the reasons that I added a 2x2 cedar sill under each of my 4 ft tall foam wall blanks, and also one of the reasons I will be putting my walls on top of my floor instead of along side like some others. With the foam construction the ceiling can sit on top of the walls, unlike traditional where the spars are generally set down into the wall panel stealing more inside height. Yeah, it means that my inside skins have to be taller than 4 ft, but I want the grain to run vertically anyway for appearance.

I think the prefab flooring could be a good thing, but you will want to integrate it into the structure, rather than just float it on top. Every piece needs to add strength, or it is just dead weight along for the ride. There will be plenty of extras and chatchki along the way for added weight, so make your main structural elements count. $.02

Test it to see if it can be glued together (many of these types are only meant to be snapped together) and see if it has a solid or undercut bottom. My way of thinking is that an undercut bottom, while reducing weight, might result in pressure points that crush the foam substrate (maybe not a bad thing... sort of bed it in), but if they don't they could reduce the glue contact area and therefore overall strength of the composite floor structure. So I guess I am waffling there a bit. Test.

My $.02 from my perspective.

[mezmo]

Another approach is to build your own "mini-SIPS" variation
on the Foamie method. This is probably the approach I'll take
whenever I get to it. One reason for this is, I do want a Birch
plywood interior - they're just too pretty to ignore for me.
Another reason is for some ease in building - something you do
need to consider among all the other variables.

Here's a repost of some info I did on SIPs for another thread
somewhere else on here, that I'm too pooped to look up at the
moment, so I'll just paste it in again here:

**********
I think SIPs are a good idea and I will probably use a form of them
whenever I get to build. [Too many house projects are a priority
at the moment.] For a larger size construction, I'd seriously look
into them. I consider them a Foamie variation.

Anyway, check out linuxmanxxx's post/builds.
Here's the link to them:
search.php?st=0&sk=t&sd=d&sr=posts&author_id=11546
He is using a small scale version of them and gives details on how he did them -
they'll be a reference for me in the future. He uses them in his business:
http://www.microcampers.com/ Just browse through them until you reach one
that pertains to his SIPs and then click on the thrtead title if you need context.

Here are some links to a SIP builder with a differance. [compared to those
SIPs that are used for house construction.] They are in Washington State,
and make many different kinds/thicknesses of them. Quite an interesting product.
http://www.superhoneycomb.com/
http://singcore.com/
http://singcore.com/tiny_index.html
http://media.designerpages.com/3rings/2 ... ing-homes/

You should be quite interested in the following:
A gal in Washington State is building a tenwide Tiny House, using them:
http://mytinyabode.blogspot.com/
And her Dad is using them to remodel a vintage Airfloat TT:
http://www.everyonecandance.com/Airfloat_Process.html

**********
To make your build usable you need to include all sorts of things
that you may require, and the easiest way to include attachment/
hard points for those, in my view, is this Mini-SIP approach.

I've also been wondering about a variation on the Mini-SIP that'd use
the stitch-n-glue boat building method. http://www.boatbuilder.org/
With that I'd basically build the inside walls of 1/4in plywood with the S-n-G
method, frame any/the openings' perimeters and the outside edges
with the appropriate size 1x wood or such, and then glue in the foam
[most likely in the appropriate shaped/sized pieces vs a large sheet]
to cover the outside of the interior 1/4in plywood walls and thus help
insulate [an uninsulated trailer is a poor accomodation in my personal
view] and fill out the form of the body of the trailer. Any seams and gaps
would be minimized while applying the foam pieces, but any remaining gaps
can be filled in with one of the canned gap-filling foams, and then all
that'd be smoothed out and then faired out with some kind of fillers to
try and make a smooth surface for the outside skin. After that, I'd probably
go with either a fabric and glue and paint or fiberglass cloth and epoxy
as the outside skin. It all depends on costs and if I could even tolerate
the fiberglassing fumes. [Epoxy is supposedly less "fumey" than the
polyester type, but I do have allergy problems with some chemicals,
so that'd remain to be seen if that could even be a possibility.] Some
kind of foamcoat is another alternative too, but they are more expensive
than the old-time fabric-glue-paint method.


Cheers,
Norm/mezmo

[Dirke]

Remember that everything you add above the wall sill is stealing away your head room. 4 ft is plenty of head room, but I have concerns that my wife might be uncomfortable in such a small space, so this is just one of the reasons that I added a 2x2 cedar sill under each of my 4 ft tall foam wall blanks, and also one of the reasons I will be putting my walls on top of my floor instead of along side like some others. .

Ok, that gives me an idea. I hadn't thought about putting something underneath the foam. I only thought about adding more foam to the top. What about making a channel out of three boards for example two nice trim boards perhaps 2 x 6s with a 2 x 2 (or 4) in between. Those would run the length of the trailer and be screwed onto your base on both sides (maybe the ends too). then you could glue your foam down in between. That would be nice and strong and give a bit more headroom. I know 2x4s aren't really 2x4 so you might have to add some sort of spacer to let the foam fit unless you wanted to use the 1.5" foam (would that lessen the strength too much?). It would be very easy to install that way as it should stand on it's own quite nicely. I would probably put the canvas on first. I bet I could use a leftover piece of laminate flooring as the inside board which would give it a nice finish.

it would definitely make installing the walls very easy. Just put glue in the channel, stick the walls in, then wait for it to dry. I know it would add a little weight bit it might be worth it for the ease of installation and the extra headroom.

Thanks!

[GPW]

D, as we’ve found out around here , you might consider making a small test “model" of your ideas just to test the design feasibility and familiarize yourself with the assembly procedure in advance of the Big build .... makes things much easier to visualize , saving time and mistakes later on ... Foam board from the Wally World is 1/4” thick , so would make an ideal 1/8 scale model of a 2” foam trailer build ... and it’s already paper skinned on each side ... very Easy to work with ...

[Wobbly Wheels]

Just to emphasize the different construction methods....

Check out the thread on building with epoxy and glass.

I'm being pretty tight about structural weight and trying to get the most from every pound I add to the build. It will need to tolerate a little bit of punishment, but nothing on the scale of KC's TCPE.
Of course, with lighter weight comes weaker forces trying to tear the thing apart.

By glassing the shell, you make an 'egg' with a single continuous structure to it. I took the SIP idea for a floor and used that, incorporating the upper skin with the trailer's inner glass skin and the lower with the outer skin so essentially I have two thin, light, hard shells held at a fixed and constant distance from each other.

Epoxy is pretty user friendly and, while it does have its own set of 'rules', they're pretty easy to pick up.
While it's a whole lot lighter, it's definitely not the cheapest way to build.

It's all about what's going to work for you...

[KCStudly]

On a 5 wide think 1x2's and 2x2's, max. No 2x4's or 1x6's unless you are cutting them up into curved segments are other smaller parts.

I do have some 1x4's embedded into my wall blanks as blocking, just to make i have something big enough so that I don't miss it with a screw later, but they are all smaller pieces...little chunks, really.

The less layers and levels you add to your floor, the less material, effort and cost it will take. Some people just bolt a piece of plywood down on top of their trailer frame and call that their floor. Depends on your goals, needs, trailer size, and budget.