Teardrops n Tiny Travel Trailers

HI, I'm still considering options, and some primary objectives are light weight and water-tightness, with a high strength-to-weight ratio for ordinary use (i.e. the cabin can withstand wind and road hazards and ordinary wear & tear). Another objective is rot resistance. A skinned 'foamie' might be an interesting option.

Instead of fiberglass/epoxy or canvas/titebond on foam, I'm considering using Tyvek and polyurethane adhesive. Tyvek has excellent tensile strength, puncture resistance, and water-tightness, but doesn't work well with many adhesives and is eventually degraded by UV light. Foam is dissolved by many glues incorporating non-polar solvents (e.g. paint thinner), and water-based glues many not be the best for exterior use, and foam is susceptible to heat generated by the curing of epoxies.

After reading through some 3M literature about Tyvek, I think it could be a good choice if used with polyurethane glue. The PU glue cures slowly, without much heat, upon exposure to water vapor and will mechanically grip the surface of the foam (without dissolving it) and the surface of the Tyvek too. It is non-toxic and oderless when cured. The Tyvek can be protected from UV light and decorated by 1) covering with printer's inks (not dye or paint!) as well as by covering the trailer with a tarp or garage during storage.

I"m doing a test right now -- gluing a Tyvek mail envelope to a styrofoam cooler with ProBond glue. You might expect a report sometime tomorrow.

Wood or metal structural hardpoints for attachments could be PU glued to the foam/Tyvek as well. I think it would be best to cover both sides of the foam with Tyvek, to create a sandwich with properties similar to a box-beamed panel.

Can you give me advice and critiques?

Oops. Tyvek is a Dupont product. I was reading around the Dupont site about Tyvek, and the 3M site for adhesives.

How are you going to deal with the expanding properties of the PU adhesive? Seems to seep out of all wood joints.

Uh-oh, I spread PL brand, not ProBond as I reported before. I spread a pretty thin coat on the styrofoam, and it bled through a little bit through the Tyvek. But so far, it hasn't foamed at all after 4 hrs. I'll post a pic soon.

If it foams more around wood joints, I'll just use a serrated breadknife, japanese handsaw, or a crankneck chisel and slice it off while it's still a bit soft but not sticky.

Bob,
If you used PL Premium it generally doesn't foam. The poly glues like Gorilla glue will foam and may lift the Tyvek off of the foam.
Take care,
Tom

Some Sips panels use a PVA water based glue. It's a crosslinked. D3. That apparently means its a one way curing chemical reaction. It does not go back to mush when wet again.

I think titebond III is a D3. I'm in the uk and use evostick exterior in the blue bottle. It turns to plastic when cured.

PU is a great glue but awful to work with and expands.

Like the idea of tyvek. There are competitive products that come in bright colours.

The PL Premium glue worked well. In a tear-off test, the glue bonded the Tyvek tightly enough so that it delaminated. The glue gripped the stryofoam very tightly as well, such that bits of foam were torn out too.

But as Grant(?) said, the PL glue is sticky to work with, and so I'll try Titebond III next which is supposed waterproof. While on the subject, I wonder if it would be a good idea to have a few removable insulation panels, so that when the camper is in storage, water vapor could pass through the Tyvek skin so as to keep the interior fresher.

Also I haven't see colored Tyvek-like materials. I did find plain white Tyvek in various lengths and widths at http://www.materialconcepts.com, and I'm investigating printer inks. Maybe an outdoor advertising graphics business could do a jazzy design, or at least offer some advice.

Did it actually pull the foam or just the imprint in the glue?

It's a little hard to tell, but mostly it looks as though it pulled away although there are definitely flecks of foam attached. I'd say that it's essentially a mechanical bond to the foam, but acceptable I think. They PL glue definitely penetrated into the Tyvek. It's seems to have a bit of a stink, at this time. I wonder how soon that will dissipate.

Next I'll try a panel of house insulation with a finer surface finish.

I would be concerned about the impact of water on your bonded system. Not all tyvek is water proof, and water intrusion could do weird things to your system.

Next test, do some high and low temp cycling, as well as some water testing. Try and get a sample of the tyvek you would use, not all tyvek is created equal.
Tom

Socal Tom wrote:I would be concerned about the impact of water on your bonded system. Not all tyvek is water proof, and water intrusion could do weird things to your system.

Next test, do some high and low temp cycling, as well as some water testing. Try and get a sample of the tyvek you would use, not all tyvek is created equal.
Tom

Good point. I believe one of the qualities is that it is water vapor permeable. If this is true, then some kind of treatment may be necessary.

Yes, Tyvek is permeable to water vapor, but not to liquid water. Thus it would equilibrate with the ambient humidity much like any other structure, unless there was a heat source (sun, electric, human body) to drive vapor out. But this would be much like any other structure. If all components of the system are waterproof and there are no gaps or voids that allow water infiltration, then there should not be a problem. (Are those 'Famous Last Words'?)

However, the issue of thermal cycling could be a problem, if the materials expand and contract at very different rates. If too much stress occurs then a joint might break apart. Hmm, maybe I should build and cover a box and let it stand outside until February or March. That would expose it to rain, snow, and ice, down to 0F or so, for weeks.

Don't forget that while you are sleeping in the cabin, you're pumping lots of water vapor into the air inside. That's not going to escape unless you provide air circulation, and convection isn't going to be enough.

<Chas>

As well as consuming oxygen and exhaling carbon dioxide -- ventilation is always necessary.

Bob Hammond wrote:Yes, Tyvek is permeable to water vapor, but not to liquid water. Thus it would equilibrate with the ambient humidity much like any other structure, unless there was a heat source (sun, electric, human body) to drive vapor out. But this would be much like any other structure. If all components of the system are waterproof and there are no gaps or voids that allow water infiltration, then there should not be a problem. (Are those 'Famous Last Words'?)

Making something waterproof can be challenging no matter what materials and techniques you use. Making something that can sustain the shocks and vibrations of travel and remain waterproof is even a greater challenge.

I was paranoid about eliminating water intrusion on my build, but knew inevitably that it was going to happen. So my approach was to build a waterproof exterior and a "breathable" interior so that any moisture penetration had a place to evaporate/permeate. The exterior is floating aluminum over epoxied plywood. The interior plywood of the insulated roof and floor is not finished. (The ceiling does have a light webbing of adhesive to afix the hull liner material.) The interior finish of the insulated sidewalls is engineered flooring. The flooring is finished but I did not edge glue the t&g joints. I do store my teardrop in the garage and leave the windows and roof vent cracked open to hopefully allow any moisture intrusion to permeate/evaporate.

Bob Hammond wrote:However, the issue of thermal cycling could be a problem, if the materials expand and contract at very different rates. If too much stress occurs then a joint might break apart. Hmm, maybe I should build and cover a box and let it stand outside until February or March. That would expose it to rain, snow, and ice, down to 0F or so, for weeks.

I don't know the different coefficients of thermal expansion, but I tend to think that tyvek and polystyrene should not have that much of a difference. A test would certainly put your mind at ease. I look forward to your continuing experimentation and reports.