Alumipanel and MDO?

[Trackstriper]

Trapped,

Nope. Nobody seems to have much interest in these materials. I thought they would be a goldmine for someone, especially for a fairly simple TD.

Many people build with solid 3/4" ply walls, then spend a lot of time prepping and painting the surface, inside and out. Or they may "float" an aluminum or plastic panel on the outside surface 'cause it seems like no one can get it to properly bond to the ply and have it stay without lifting and bulging from the surface. I would think that the floated skin would have to allow moisture behind it if the trailer is ever in a wet environment. Guess it's not a problem. I would think the 1/2" double skinned Nu-Alum (or a similar product) would be great for a 4x8 or 4x10 side-profile TD. I'd bet it would be a good bit lighter, stiffer, and more stable than finished 3/4" ply, and cheaper in the long run, at least if you pay yourself for the time and materials you spend finishing raw wood. It certainly wouldn't fill everyones' needs, but I've mentioned these specialty sign maker's materials several times on the forum and seems like I can't even get a debate going about the evils of using a product like this. Maybe this will spark it.

I'll be building a tiny travel trailer (if 12' will qualify) and am leaning very heavily toward an aluminum composite product called AlumaCorr (10mm version), manufactured by Nudo. I'll probably be insulating the walls and using AlumaCorr for my outer skin as it's very stiff for it's weight (22# for 4x8 sheet) and very weather resistant. AlumaCorr has a corrugated core that acts as a very decent thermal break between the skins, although not much of an insulator. It's also available in 4x12 sheets and that has an advantage for my size trailer, one horizontal seam at the beltline. There's also an interesting product called Polymetal (3mm version) that would do well but it's max length is 10' and I don't think I want a vertical seam in the side. Anyway, they have been great materials to work with in small test panel sizes. To be fair, I haven't built a trailer with these products but that's where I'll likely put my money when it's time for sides; else MDO ply.

http://www.alumapanel.com/subcategories.cfm?lines_id=289&step=1

J.B.

[chief5]

trackstriper,

I too have thought this type material would speed up construction by eliminating the exterior finishing. How do you bond it to the framing? I don't really want visible screws from the outside.

Thanks, Lorn

[Trackstriper]

Good question, Lorn. I mentioned several materials, but they are all effectively clad with .013-.015 painted aluminum skins. Here's what I have played with so far.

I took a piece of the Polymetal and glued 6" long sections of 1x1 square aluminum tubing to it. I locally sanded the paint finish of the Polymetal to knock off any gloss and provide some tooth for the glue, and I sanded the aluminum tubing lightly as it was powder coated in a previous life as an aluminum fence picket. I tried several different glues: PL brand polyurethane from a "caulking gun" type tube, Gorilla glue, a moisture cured polyurethane binder that I had from work, and regular-set JB Weld epoxy. The JB Weld generally worked the best for metal to metal, and the Gorilla glue and PL adhesive also worked well once set. One of the problems with the poly glues was that there really wasn't enough moisture to get the cure going, it was like keeping the glue in the tube...it would set near the edges of the joint but would take a long time for enough moisture to get toward the center of the bond. The JB Weld, being a two-component material didn't have this problem and had the quickest set overall. I also glued a piece of 3/4"x1" (actual) pine with the Gorilla glue. This worked well as there was enough residual moisture in the wood for the glue to set, don't recall if I moistened the face of the wood prior to attaching. I don't think that I clamped any of the joints, just lightly buttered the tubing and mushed it down onto the Polymetal, but these were fairly short pieces of tubing and the fit was reasonable.

I then attached a piece of the tubing with an affordable sign maker's grade of bonding tape (not 3-M VHB tape). I used two parallel strips of 1/2" wide tape to get maximum surface contact. Then I let the whole thing cure for a couple of days.

My polyurethane running track binder didn't cure well (but eventually set up)...fairly poor performance. The JB Weld did well, as did the poly glues once set, plenty strong. The bond to the wood with the Gorilla glue was similarly very strong. What surprised me was the bonding tape. While there was some flex in the joint as the bonding tape has a foam core, I could not break the bond with my bare hands. I cut the section with the tube with the bonding tape away from the rest of the samples, then hung it up with a sixty-pound weight, trying to shear the joint between the tubing and the Polymetal. It failed in about a week by shearing at the middle of the foam core...it left the adhesive bonded portions on the tubing and base metal. These bonding tapes typically have a permanent-loading shear strength of about 1 to 2 psi. I loaded it to 10 psi for week before failure. Intermittent shear loads on these types of tapes can go above 150 psi.

This is all without mechanical fasteners, which could be helpful.

More later...time to interact with wife.

J.B.

[mikeschn]

You still do that? Oh no!!! Too much information!!!

Mike...

More later...time to interact with wife.

J.B.

[chief5]

Definately not too much information. That is exactly what I was asking! Oh, you mean about the wife thing! Just kidding. Thanks for all that info J. B.

Lorn

[Trackstriper]

Mike,

Still do!!!

But, I had promised Suzan we'd watch some Northern Exposure episodes on DVD tonight. She needed a break from some things that were on her mind.
Happy birthday to Chell. Hope she had a great day. We're all glad that she gives you the time to keep this thing together and encourage us.

J.B.

[Trackstriper]

Back to Lorn's question,

The Nu-Alum has a 1/2" plywood core, so I would think that wood stringers could be screwed and glued from the inside of the trailer with the appropriate length screws. The screws would not dig very deep, but if you used a fair number, they would act as clamps to hold the glue joint tight. The primary strength would be in the bond but the mechanical fasteners would be backup. Bulkheads could be glued and screwed to the stringers. If you wanted to have something to support the side panel of the tear, you could bond a 1x3 to the lower inside edge...doubt you'd pull that off. It would take some design planning because, as you say, ya don't want to run the screws in from the outside.

With the Polymetal, you'd have to rely on glue bond, but you could run some nice screws in from the outside at the frame level if you wished, give it a riveted look along the bottom edge. If you bonded aluminum angle or tubing to the inside of the Polymetal, you could mechanically fasten with blind rivets. Lots of ways to go.

This is the wall system that I'm strongly leaning toward at the moment: 10mm Alumacorr outer skin/structural panel...1"sq. aluminum tube studs, glue bonded to the AlumaCorr...1" rigid polystyrene insulation between studs... .030 or .040 interior skin bonded to studs with the bonding tape. The "grain" of the corrugations in the Alumacorr would run horizontally so it needs to be stiffened in the vertical direction...studs. The AlumaCorr acts as a thermal break to keep heat/cold from transferring directly through the aluminum studs. The bonding tape (also a thermal break) is somewhat structural when you have enough square inches of it working, but at the same time it will "lozenge" so that if the temperatures of the outer aluminum skins and the interior aluminum wall skins are different, it will allow for the difference, rather than have the structure fight itself. In essence, the inner wall skin will "float" like the aluminum on the outside of many TD's, but if there is structural shock load, it will help with that load.

By staying with one primary material, aluminum, I can have the following advantages:

1. There won't be much issue with different coefficients of expansion of different types of metals (for the body structure).
2. The aluminum won't rot if water should get into the body structure.
3. Aluminum isn't good food for the mildew that we get in the south (allergy issue).
4. Aluminum doesn't off-gas formaldehyde that my wife and I are allergic to.
5. The aluminum is pre-painted at the factory, so the prep has been done right (in theory!) and will require no additional finish unless I want to add it.
6. Easy to keep clean, inside and out.
7. Should be light. A rigid, all metal, pre-finished, insulated sidewall about the weight of 1/2"plywood.

It's not the cheapest way to build a trailer. Of course, this is simply Trackstiper's theory, but I've been thinking on it for a while now. That's one reason I haven't dug into this project as far as actual construction yet...it's complicated and I only want to build this special trailer once.

J.B.

[Trackstriper]

Yep, those 5x10 sheets of Polymetal or Alumacorr are mightly tempting. I'm just going to need to go 6'x12' (floor) to get it all in. I played for about a week with a smaller 5'x10' (floor) design that could work, and be much simpler to build, but I think it would be too small for a several week's jaunt. I too will have to go four seasons. An angular design would be much easier to work with, but I'll probably go with a curved roof.

The unpainted MDO can be gotten in the 5'x10' sheets, but not the aluminum skinned plywood, Nu-Alum...those sheets are 4'x10' max, unless you have a different supplier. Also, a potential problem that I see with the single sided aluminum ply is that the backside is covered with what they call a "poly backer". I suspect that in order for the sheets to be dimensionally stable and not warp with humidity changes, they have bonded a moisture barrier to the backside. Don't know if you could glue to this backer or not. Possibly it can be skinned through with a router to get to the raw wood for proper gluing.

Keep thinking!

[bobhenry]

On an old post I had a link to Citadel Products. They provide Interior and Exterior glazing and accent panels. They had on that really interested me. Polished Aluminum on both faces an interior and exterior homeycomed polypropelene and a center core of beaded styrofoam. Their products were diverse and several came in 4x8 5x10 and some in 6x12. The colored panels are truely gorgeous . There are splicing splines to join the panels as well in a vaiety of configurations. Running splines inside corner outside corners ect. I would build it to be accented with wood trim to hide all attaching points aroung the perimeter of the panel. I am not quite sure about how best to make the galley wall connections. I am certain that damaged panels of this type of product should be available at a greatly reduced price. Rounded teardrops seldom need the corners and this seems to be where the panels get damaged in shipment. Maybe I should call them again an inquire about damaged panels. We have a large distributon warehouse in Indianapolis. One of our fellow forum members stopped over and they were not interested in selling one and two sheets. I asked for and received a sample case and the full products catalogue at work assuming a salesman would follow up. No one ever bothered.

[chief5]

Thanks for all the great info J.B.!! I'm going to order some samples myself. I'm afraid the MDO product will be HEAVY. I am leaning toward the 1/2 ply core with screws and glue from the inside. Wood framing though as I have wood skills and no metal skills (or tools).

Thanks again, Lorn.

[aggie79]

Trackstripper -

Thanks for the research and product info.

What were you thinking about to use for the roof construction - particularly the skin?

[Trackstriper]

bobhenry - I've seen architectural panels like that at various sites on the web but I kind of get the impression --could be wrong-- that if you want a building's worth of the product they'll make up whatever you want, within their capabilities. I suspect that it's run as a lot and shipped to the job site...not like there are any panels just hanging out on a rack somewhere hoping a customer will walk through a door and buy a couple. The honeycomb products should be considerably stronger than the AlumaCorr, but at what price?

Lorn -As I recall, the last MDO sheets that I weighed were about 42-44# for a 4x8 sheet of 1/2". The hardwoods dealer that had the MDO told me the core was fir plywood, which is reasonably light for a plywood. It's about the same weight as the aluminum skinned 1/2" ply, but don't quote me on the weights. Were you thinking about MDF (medium density fiberboard)? That stuff is fairly heavy me thinks.

aggie79 - Thinking a roof thickness of 1.5" insulated with two sheets of 3/4" polystyrene for bending, will have to kerf the insulation in areas where the bends are tighter. Maybe use .026 or .032 painted aluminum for the "headliner", probably bonded to the spars with bonding tape like the inside wall panels. (The primary reason I'm going with the metal is for the allergy reasons...my wife and I are both chemically sensitive, she more than I. Actually, If I could find a small commercially built travel trailer without the formaldehyde issue and mold propensity.......hmm, a new shiny Airstream with the bare aluminum headliner would do the trick, but I can't afford that stuff! Back to reality.) I haven't totally sorted out the spars yet as far as actual material. I scored 35 pieces of 1" square aluminum tube - about 16 gage - last year at a scrap metal yard. They are about 66" long, powder-coated fence pickets from commercial aluminum fence. I may use them for the studs. I'll have to scrounge for the spars or breakdown and buy some tubing. Might be able to find some hat sections. Gotta be aluminum.

Left that outer skin for last, didn't I. One option is that I have a local semi-trailer repair facility nearby and they can sell me the 108" wide .040 roll stock at a reasonable price, by the linear foot - whatever I need. It has a mill finish but it looks almost like it's lightly brushed, not bad. I could do the roof with this material using a single sheet which has obvious advantages. Downside is that it's mill finish and I don't think I want to do the polishing maintenance or live with a dull gray finish. I think I'm preferring just a plain white trailer for my purposes, nicely done but not flashy, something that will "blend in" a little. White reflects the sun's heat pretty well. Prepping that mill finish for paint might be tricky. It's got a light oil on the surface to start with. That's where I like the factory painted panels, even if they ultimately needed to be painted over the base paint should have been well prepped. So, the other option is to buy some 60"x144" sheets of .040 white, have them sheared in half and rearrange them as a sheet 72"x119". That lost inch is for a glue bonded lap joint. My test with the PL adhesive was quite good on a 12" wide sample, once the #@!*% glue actually set. I think a two-component urethane or epoxy is the way to go, unless you are bonding to wood where the poly glues seemed to set in a reasonable time. I would need to have several transverse roof seams. Don't think that would be a problem.

I've got some Sketchup drawings in my album that might give you an idea of the general design of the trailer. The 12' version is the current plan, but those drawings are not developed as well as the initial 10' version. The 12 is sort of a stretch version of the 10, same layout...a little more length for beds, closet, shower/porta-potti, galley. AC forward in nose. Flexiride half-axles to allow for dropped floor aft of beds, 67" aft headroom for 65" wife. I'll have to bend a little.

J.B.

[chief5]

J.B.,

Your'e right. I read MDF when you wrote MDO. Man that would make for a heavy trailer.

Lorn.

[CADLAC]

I am an airline mechanic and we see what is called oil canning between the riveted areas. That is due to the flexing involved. I had thought about building the frame of aluminum and riveting the skin but the more I see the oil canning on our aircraft the less i like the idea. I am looking to a aluminum clad material to build with. and I am looking for pre-manufactured doors such as those on the Cozy.