Thrifty Alternatives ..Building Foam Campers

[John61CT]

Yes, with no metal structural framing lots of flex required.

But maybe enough:
> An overcoat of Sculpt or Coat prevents paint from flaking off when flexed. For additional strength, add a thin layer of gauze or cheesecloth.

[Pmullen503]

I've been using Sytrospray for years on foam RC airplanes and I can say that it stays somewhat flexible for years which is probably a good thing if you want to use it without fabric. I don't about the other products mentioned but if they are brittle when dried that may not be good.

Other than the textured finish, PMF seems like a good way to go. Putting Sytrospray over canvas would get you a sandable smooth surface if that's essential.

[linuxmanxxx]

Styrospray lists the shore scale hardness and it's impressive. Hoping the other 2 have similar properties. Hence the eventual testing. They are latex based so they probably won't be brittle.

Sent from my Pixel 2 XL using Tapatalk

[Pmullen503]

If I were going to skip the canvas, I think I would recess some plywood gussets or braces into the foam at potential stress points. Like near where the hatch attaches or the door frames. I'm thinking 1/4" plywood "L" shaped braces with 1 1/2" wide arms glued into slots in the foam at the roof/wall joint.

I really like the idea of wrapping the side canvas around and under the floor as a way to keep the sides attached to the floor. Though maybe you could recess some plywood splines into the foam and floor to tie them together.

Other than that, if the one part coatings have the same tensile strength as Styrospray I wouldn't worry about the trailer coming apart.

[John61CT]

I'd be surprised if there's much **tensile** strength at all in any thin coating by itself.

Even the strongest epoxy needs the fabric matrix for that.

Resisting puncture, protecting the friable foam from wear & tear, sure, but not tensile.

Not to mention holding large panels' glued edge-corners together under 100s lbs of stresses without any other framing.

[linuxmanxxx]

I'll update you after some testing unless someone else beats me to it. I'll pick some up in the next week and give it a whirl when weather permits. Seems lately all it does is rain here.

Sent from my Pixel 2 XL using Tapatalk

[GPW]

Been raining a LOT here too … Anxious to hear of your testing Steve !!! All this rain , I may have to build a Foamie Boat …

“ I really like the idea of wrapping the side canvas around and under the floor as a way to keep the sides attached to the floor. “ One little point , as we found from experience , if you do wrap the canvas around under the floor , make darn sure it’s Completely WATERPROOF … or provide some sort of drip edge to keep any moisture off the underside . Just the morning dew alone will drip down and find it’s way into the smallest of spaces that are not completely protected … ( ask me how I know )

And while we’re attaching things , you know to date there hasn’t been even one incident of a Foam cabin separating from a trailer floor …. not without a Sawzall… Just sayin’ …

If we’re looking for a better way to attach the wall to the floor , I’m sure we can find a way that doesn’t depend on any outer covering for attachment strength … Since we all now accept some lightweight framing inside , it becomes easy to add some inner wall to floor attachment structure …
Not being able to resist making a drawing , here’s just one idea ...

[GPW]

… and then you could even work out some slots and tabs for “interlocking” assembly ...

[linuxmanxxx]

I was just looking at the FAQ and it says to add fabric only if you are covering bead foam or paper. Since the majority are using the blue or pink stuff it would be very strong to coat it directly over the foam. It's the consistency of whipped butter in the pail and in that state has to be troweled on or spread in some form. Thinning with hot water it can be sprayed with a hopper sprayer and is what I think I'll look at doing. It can be applied up to 1/4" thick and stays flexible unless thinned too much. I'm thinking 1/16" or 1/8" would be perfect and cost effective.
Steve

[Pmullen503]

… and then you could even work out some slots and tabs for “interlocking” assembly ...

I like the "thin sheeting", something like 1/8" plywood glued to the foam to spread out the forces. Add some biscuits or splines to tie it into the floor and I think that would be a very strong system.

RE: drip edge, I need to do that on mine as water crawls around the edge and it sits between the frame and floor. I was thinking wood triangle stock around the perimeter with another piece of PMF wrapped around it going about a foot up the wall. Then just a paint line to camoflage the joint.

[John61CT]

I was just looking at the FAQ and it says to add fabric only if you are covering bead foam or paper.

They have only conceived of using it to protect against surface wear, not trying to hold together boxes made from large foam sheets joined at 90° hurtling at highway speed without any other structural support.

But of course have a go, just start out slowly and on empty roads. . .

[linuxmanxxx]

Do you not understand that people have built numerous ones covering foam with canvas and gluing canvas to foam with wood glue and/or latex paint?

Some people have taken those two items and checked how well they glue straight foam to foam together and it was quite disappointing. So if wood glue on foam with canvas can hold going down a road, I'm fairly certain a flexible hard plastic shell should do just fine.

Plus I frame it all with light wood and glue/screw that portion together so don't think I'll have problems in traffic.

The stuff is like glue and covering an entire surface adds massive strength because of the large surface adhesion properties. Plus the inside will be using something glued to it as well so that it's completing the torsion box type principle that the foamies are all built around.

I'm more worried how it'll hold up in west texas 100 plus summer temps than anything else. If this fails I'll use styrospray 1000 since I know it's as hard as the outer plastic of a golf ball and UV stable. I'm just looking at this because it's much cheaper and Glen has helped me see the light of cheaper and works is quite good.

And the final reason for this over canvas is that it can't rot or suffer water damage at all. The foamstream had to be remounted due to issues with waterproofing canvas and edges and won't be an issue using plastic.

And fiberglass and epoxy on their own have bad flex properties and get brittle in sunlight so that is why cloth is added and the surface is painted or coated as well.

Water based products totally rock whenever you can use them since almost no fumes and toxicity is pretty much zero.

I've built 3 campers using sandwich foam construction and water based contact cement and with minimal wood and complete glueup I could walk on the roof with little flex and 1 1/2" thick ceiling and only 3/4" walls. 1 was aluminum over luan over foam 1 was aluminum over foam and 1 was frp over luan over foam. The strength was the sheer strength of the fully glued surfaces on all 3 of them because otherwise foam would never support 200 pounds walking on it.

Any of the 3 I listed will more than likely work I'm gonna test the cheapest option on cornhole boards first and then a camper. If it doesn't work I'm out only 30 bucks no big deal. The styrospray is 2 parts and 3 to 4 times the cost but actually lists all their properties because it is a full blown chemical manufacturing company. I was impressed that they have pictures posted showing movie sets that used this as well as the harrah's casino in reno having a facade made from it.

If this works it should wind up being cheaper than the canvas route and more durable. Certainly a win for the frugal minded builder.

Fabric would make it stronger probably but doubt its needed.

4 yrs ago I thought people were crazy putting canvas and wood glue over foam well heck I was wrong indeed and we still haven't had any turkey or bird strikes on one to see how it would fair and I hope we never do.

[Pmullen503]

I'd be surprised if there's much **tensile** strength at all in any thin coating by itself.

Even the strongest epoxy needs the fabric matrix for that.

Resisting puncture, protecting the friable foam from wear & tear, sure, but not tensile.

Not to mention holding large panels' glued edge-corners together under 100s lbs of stresses without any other framing.

Styrospray at least adds lots of tensile strength. Granted I'm using a very thin layer on 1/4" foam but in my tests it's comparable to epoxy and glass cloth on a weight/weight basis. Coat both sides of 1/4" piece of foam and it turns into something different, you can't tear it with your hands.

Remember those stresses are spread out over 100 or more square/ft riding in the slipstream of a tow vehicle. Having used it for years on RC airplanes I wouldn't have any qualms about using it on a trailer.

[John61CT]

My point is not as much the tensile strength along the flat 2D of one sheet.

It is at the heavily stressed 90° edge joins.

Of course if a wood or other strong frame is handling those, or if the hard-shell finish is the outer-finish-only over a PMF build, totally different story.

In any case, no point in arguing further in the abstract, I've registered my concerns, and

enthusiastically encourage anyone willing to pioneer / test their ideas and enhancements to do so.

[GPW]

Guys , how about a Thrifty test … make a 1”+ 1’ scale model of a simple Foam trailer ( to pull with your RC car or Monster Truck ) with a Styro spray outer covering … Quick test for application and appearance , inexpensive as not much material is needed …

We saw some “Flex Seal” for sale in the grocery store ( as seen on TV) … Wonder how that would work … ??