A more durable Foamie?

[gizmotron]

This is the only concern that matters. I have hanged my hopes on acceptable fomie building practices. Wings of minimal stress capacity have been checked beyond reasonable capacity by pilots of disputable expertise. Yet they go up into the wild sky beyond yonder with their contraptions anyway. We are grounded at below 80 miles per hour, (ever been to Idaho?) You can't believe the power of wind on a pile of crap foam dog house. Am I just being a dope in all this? I want the thing to be light as a feather and strong as a snowflake with an ice nine resolve. ( get that reference? It's political and that grandson living in your basement.) That of course can never be. But a strong composite "Drop" can be the reason that this experimental website, and fomies, is why we figure things out in the first place anyway.

[KCStudly]

Whole lot of speculation going on here. In foamie circles we like to test. If in doubt test.

Do a medium/small scale test. Get a piece of foam board and scuff it up, a yard of canvas from the fabric store, small bottle of TB2 and test. Do the same with the waterproofed fabric. Compare.

Now, don't be surprised when you grab the edge of the fabric and peel it back slicker than snot. That's not really a valid test because it's not really how the composite will be loaded in use. Try to bend the panel; it will flex some but will likely not fail. Try to pull the canvas off of the foam in a straight line parallel to the bond; I bet you can't.

Then decide if PMF is right for you. It is what it is and it works well for many people. Don't disparage if it isn't right for you.

I did some tests and decided that I wanted to go with epoxy and glass, but I can tell you it was a very close call for me. Epoxy and glass is no picnic; it costs a bunch more and for a newbie, is much more complicated.

[gizmotron]

I've read where Gripper Primer paint on the outside gives rigidity to the fabric, where TB2 on the outside does less. I've seen video of PMF tests and what sticks the best. In all the examples the PMF is flexible as it is pulled away from the foam. It bends without cracking. The only way to get the fiberglass and epoxy off is to delaminate the composite. If the stringers are properly attached to the glass/epoxy, the top laminate will have to pull the bottom laminate through the foam in order for it to separate. So the method to bond the stringers to the both sides of the surfaces is the critical task, be it epoxy/glass or PMF. I seem to recall that in the days of wings made of aircraft spruce, they would glue fabric to parts of their wing ribs in order to hold them together.

I wonder what would happen if I took PMF and applied it to the sides of the 1/4" stringers? Fabric would be extended beyond the stringer's edges so that it could be layered into the depressions on the surface of the foam. This would have the effect of bonding the two sides of the PMF composite together. The video of the PMF looks clear that even though you can peel loose the PMF from the foam, you could not easily rip the PMF itself. It's like super thin and extremely resilient leather.

[KCStudly]

It's like super thin and extremely resilient leather.

Not far off. I have a test piece roughly 10 or 12 inches on each side, IIRC just 3/4 thk blue foam, PMF on one side. I can take that and bend it around quite a ways back on itself, canvas to the outside of the bend; it flexes but does not tear, crack or delaminate; and then it comes back flat again. If you tried that with straight foam it would snap, but with the tension side held intact by the canvas, the foam just goes along for the ride. It is really quite amazing.

Now this gives the foam a lot of toughness and strength in one plane. If we take that and design in sufficient lateral support (be they foam bulkheads, arches, cabinets, inner panels, door frames) and add hard points for ease of assembly and attaching other fixtures (lighting and light switches, coat hooks, cup holders, whatever), then the unity of the structure starts to really take shape and we end up with a reasonably light, sturdy little box.

It's a nice little design challenge. Would I do it again the way I am on TPCE? Probably not. Neither of my TV's are load limited, and I think I could get done much quicker using more traditional methods (i.e. thin ply skins in and out) building a much more utilitarian camper (i.e. less fit and finish and more wood, glue and paint). With outside ply skins I would definitely reconsider PMF for the outside rather than epoxy/glass or aluminum skins. $0.02

[rruff]

So, I'm going to put stringers in the walls and roof, shave out 1/8" depressions at every stringer on both sides and epoxy & glass the 4" wide depressions. That will put a coat of fiberglass and epoxy in the depression, bonding the stringers to the surface of the foam. Later a surface coat of fiberglass and epoxy skin bonds the combo wood & glass I beams together with the 2" thick composite method. This is the only way to build bomb proof. It's not that the foam can be pulled apart and delaminate because the bond is broken at the foam's surface. It's that the fiberglass skin must fail first, and that is unlikely. This is what works for composite aircraft. This will work for the takeoff speed of a medium sized Cessna. That's around 60 MPH not considering headwinds. There is no way that I can trust TB2 to TB2 composite construction. I would love it if that was good enough.

Plenty of people have built big PMF Foamies and they *do* hold up. Follow best practices and you should have the same experience.

On the other hand, nothing wrong with wanting a more durable structure. I've pretty much settled on panels made from 3mm Okoume interior, 1" thick foam and redwood stringers in the middle, and 1708+6oz epoxy, with a gelcoat finish. The fiberglass outer skin actually saves weight and money compared to using ply+6oz (glue for the ply actually adds a lot of weight), so maybe I'll beef it up a little.

I'm still figuring out which *cheap* epoxy to use. I made a bunch of samples using US Composites medium hardener. It seemed brittle but I figured that was the nature of FG. Then I got some even cheaper epoxy from Pro Marine. They say not to use below 75F, but I did and it seems great; hardened more slowly but ended up much less brittle. I emailed them and they advise that it will not cure properly if it's too cool, so I guess I prefer epoxy that isn't fully cured? Sure seems like for this application a bit more flexibility and toughness would be preferred. PMF has that but it's too far over on that spectrum for my tastes.

Regarding "bonding the stringers to the surface of the foam" I'm not sure what you are trying to acheive (for a lot of extra work). That isn't a critical bond, rather the foam and stringers need to be very well bonded to both face skins. Also note that if you want a reasonably nice smooth finish on your FG skin, you'll need to work hard smoothing your foam-stringer surface ahead of time. I'm not going to be so picky on mine.

I've been texturing the foam with both a carpet seam roller and the wallpaper perforator, and laying down a layer of epoxy+microsphere paste to fill the texture. I don't let it dry, but layup the cloth and epoxy right after, using a FG "bubble buster" grooved roller. I've gotten the total weight of the FG layer down to 2x the cloth weight which I think is quite good considering the texture fill. It sticks to the foam really well, the bond being much stronger than the foam anyway. The bond to wood is also much stronger than the wood.

[gizmotron]

Regarding "bonding the stringers to the surface of the foam" I'm not sure what you are trying to achieve (for a lot of extra work). That isn't a critical bond, rather the foam and stringers need to be very well bonded to both face skins.

The point is to bond the stringers and the point where foam contacts the stringers to both sides of the face skins. That's why the foam and stringers need to be an 8th inch narrower, at both surfaces at the joints, so that the PMF may layup a flush layer beneath the existing surface of the foam.

So, instead of a single 1/4" stringer I'm going to sandwich two layers of 10 ounce canvas, 6" wide each, with TB2, between two pieces of 1/4" Sande Plywood cut to 1 3/4" strips. So, each section will include a stud, attached to a rafter, attached to a stud for the other side of the trailer. It will go up barn style working from the front to the back, one section at a time. I believe that PMF will be strong enough if I take these extra steps to prevent separation.

[GPW]

Gizmo... Best thing here is NO RULES.... You build it like YOU want to... all we ask is you take plenty pictures and tell us all about it ...

*** actually the worst thing you can do is overbuild and that’s never bad, just a lot more work and Heavier .. NBD

[gizmotron]

Thanks GPW, So I might substitute fiberglass 6 inch mesh tape meant for sheetrock work. That would be sandwiched between doubled quarter inch stringers. The stringers add 35 lbs to the already estimated 80 lbs of foam. If I were to use single stringers that only adds 17 pounds.

Anyone not satisfied with gluing fiberglass mesh tape to foam with TB2 ?

BTW, those depressions in the foam, at each stringer, are done with a Stanley 10" Surform Plane. I plan on adding 45 degree crown molding foam at the top edges of the inside so that I can make some large rounded sculpting on the outsides. I plan also to do some "Frenching" on the front driver side to recess my fold out pedestal for my satellite TV dish.

I will first try to take out the depressions with a palm router. If that works then the Surform is redundant for the depressions. I need the thing to round the edges though.

[seanc]

I don't know how I missed this thread, There are so many great ideas in here!

THANK YOU to everyone sharing test results!

rruff - I wish I still lived in New Mexico so you could check out my foamie camper. I am very excited to see how yours turns out. i'm sure when I build my next one I will be stealing many of your ideas

[GPW]

Guys , we’re all here to freely share our ideas and test results … With everybody doing a test and reporting results , over the years we’ve amassed a great deal of information on Foamies and what works and what doesn’t , and allaying all of the original fears of the material suitability ( doubt ) …

Gizmo, that fiberglass sheetrock tape adds tremendous strength for it's weight … can’t go wrong with that ...

[rruff]

I am very excited to see how yours turns out. i'm sure when I build my next one I will be stealing many of your ideas

I will try to thoroughly document my failures anyway! Hoping for the best.

Don't know if you've seen it but here is a PMF-foam truck camper build. http://tnttt.com/viewtopic.php?f=55&t=64361

[seanc]

Rruff - I've seen that truck camper, In fact, I'm sitting in it right now!

Here's anr idea I had for supporting the roof on an extra tall and wide build. Laminate a 2" 4x8 sheet of XPS with 1/8 Luan. After the glue has set, rip the laminated sheet into 4" strips on a table saw. laminate the newly cut sides with Luan. Now you have an ultralight and stiff box beam of roughly 2" x 4" dimension that can be turned on its edge for extra strength. What's more, you can finish it to look like solid wood. I think these would make terrific beams on a high ceiling build.

Instead of ripping the "beams" on a table saw, use a jig saw, router or cnc to cut the laminated 4x8 panel into curved beams, this would make for a very consistent/strong/light way to create a roof with a side to side curve.

Maybe this has been covered, but I thought it was worth sharing!

[rruff]

Maybe this has been covered, but I thought it was worth sharing!

That will absolutely make a strong, light beam.

For a roof beam you only need stiffness in one direction, though. If you wanted to minimize weight you could just use ply on the top and bottom, and pmf on the sides. Foam I beam.

How is the camper doing?

[GPW]

And a bit later on … you know the more we discuss the durability of a Foamie , the more the Foamie out in the driveway proves the whole system … and mine’s not made with optimum materials , ( beaded foam- EPS) . But it just sits there through all kinds of weather , and now with drip edges it drains properly and there’s nothing that stays wet …it remains pretty much unchanged , except for one little thing .
Being outside , it gets “dirty” …( outside, everything gets dirty ) , which would suggest an easy to clean finish , which an extra coat of primer or two might help making a smoother surface… Gloss paint too !!! ( Think : washing the beast)
Keeping it inside , it would only get dusty … “ Dust never sleeps” …

It’s been how many years now ? Maybe it’s now safe to say that a Foamie camper will actually work and is very "durable “for what it is ! ( but might just require an occasional washing )

[Mary C]

I've been to Indiana twice, north ga 7 times, Alabama 3 times , to Texas 6 times and now I'm in California and its three years old. I built it with the proven methods and have only my own bo bos to complain about. The whole idea of foamies was to get us on the road and I have a date with Alaska.

Mary C