Very light and no wood at all -- possible?

[Jack Olsen]

The strength and lightness of coroplast has always intrigued me. It reminds me of bamboo, one of nature's strongest and lightest building materials.

I've wanted to make coroplast beams and laminated sheets before but could not find a way to glue sheets together. A floor made up of 3 or 4 thicknesses of coroplast would be about 4 times lighter than wood.
But lately I've tried using some of the "super" tapes and glued canvas and believe that it might be feasible to re-visit the coroplast idea. Amazing what some people are doing with it. Check out this coroplast boat: http://www.instructables.com/id/How-to-make-a-coroplast-boat/

In my own trailer the floor is 1/4" fir plywood and is only doubled up to 1/2" where I actually walk or stand. Not as rigid as 3/4" plywood but much lighter.

Funny you should mention that. After seeing polygal (or Coroplast, or corrugated plastic, or polypropylene) used for a sign in the neighbor's lawn, I had the same idea. I have some samples on the way, and my thinking is to use 3 layers of 4mm thick sheet, with the grain/fluting alternated. By what I've researched so far, adhesives are the real trick with that stuff. But Marine Goop, Gorilla Glue and some types of superglue are three things I'm going to try.

http://www.christinedemerchant.com/coro ... -test.html

It's the leading candidate right now for my floor because -- unlike some honeycombed aluminum composites and other products I looked at -- its price isn't too crazy.

[mikeschn]

Jack,

I looked at Coroplast a couple years ago, but couldn't figure out a way to glue it up. Paul Elkins uses zip ties to tie everything together. Ah, just found this: http://www.christinedemerchant.com/coro ... -test.html

I should have ordered some samples and played with it. It'll be interesting to see what you come up with.

Mike...

P.S. And now I'm wondering if coroplast can be cut with a router bit??? Edit: Apparently it can be cut with a Donek drag knife. Check this video starting at the 8:55 mark. https://www.youtube.com/watch?v=fOf_tCefl6Q

[aggie79]

I've been intrigued by the fluted aluminum composite material for signs and have not doubt that it is plenty strong for walls and floors alone. It could probably be cut into strips and used for spars.

The wall to floor joint could be aluminum angle and VHB tape (or structural adhesive). Likewise, aluminum angle could be use for "hangers" for the ACM beams.

The difficulty with using this material is how to attach the roof skin. I haven't been able to think through this part.

[ssutton]

And now I'm wondering if coroplast can be cut with a router bit??? Edit: Apparently it can be cut with a Donek drag knife

I have done both on my CNC table. The router bit makes a mess of the material, I tried various speeds and feeds and also several bits. Single flute, upcut, downcut, and multi-flute spirals. Maybe I quit trying too soon but I never found a solution that worked. However, it does cut great with the Donek knife. The other real issue is adhesives that will really stick and bond. I work in the plastics industry (http://www.flex-drain.com/) making drain pipes and our primary material is polypropylene. One of the issues with making it bond is the fact that the virgin material is doped with release agents so that it releases from the molds during manufacturing into the final product. This agent is very slippery and almost nothing will stick to it. I have tried various glues with little success. Possibly cleaning the material with a strong solvent before gluing may increase adhesion? Hope that helps some.

Scott

[Jack Olsen]

I'll start off by reminding everyone that I'm the dumbest guy in the room when it comes to polypropylene. But based on my Googling, it seems like some of the corrugated plastic out there has gotten a surface modification called 'corona treatment,' which changes the 'surface energy' of the material -- which is something I don't understand in the least, except that I've come to believe the stuff is more friendly with adhesives when it's had this treatment. And the simpleton's test for whether your coroplast/polypropylene has been treated is to spray some water on it. If the water beads up, your 'surface energy' is in retrograde or some such, and you're going to have poor luck with your glue. I just tested the 4mm samples that came in the mail today, and the water did not bead, which I think means I'll have better luck with my adhesion tests. The finish on these sheets is not glossy at all -- it's more like a satin or even matte. A small sample I got from a printing supply place felt much more slick in my hands.

If polypropylene hasn't been corona treated, some people use an open flame (a flash treatment) to change the surface. Some people use abrasives, although I'm not sure if the goal of this is changing the surface energy or simply creating something for the adhesives to interlock with.

All that said, I think there's a good argument against using this stuff in ways where its adhesion (or eventual possible lack thereof) would mean structural problems for your camper. I like the idea of using it for a floor, partly because I would box it in with aluminum angle stock, which would be attached to the polypropylene with both adhesive and some mechanical fasteners.

My initial thought had been that I would get more rigidity from three layers of 4mm polypropylene. But comparing these somewhat-floppy samples to the more-rigid 10mm stuff in my neighbor's yard sign, I would now probably lean toward a single sheet of 10mm poly, with possibly a second 4mm layer (running with perpendicular flutes) in the living quarters part of the camper.

To get great rigidity from the three-layer approach, I'd need really great adhesion. Some users out there recommend woodpeckering the surface of the stuff with a spiked roller to gt better mechanical interlock. But this makes me nervous, since the floor will be getting a fair amount of stress in the course of being in towed, which would be persistently working to undo my gluing. A single layer seems more reliable.

I'm also surprised by how the stuff is rigid pretty much regardless of the fluting direction. My worry had been that it would be strong in one direction, floppy in the other. In my holding the samples, this is less the case than I thought it would be.

Still, I'm going to try a handful of ways to stick the stuff, and see how it works out. I think it would make a pretty good floor -- but time and testing will tell.

[JuneBug]

True. But structural adhesive can hold just about anything. It's slowly replacing welding in automotive assembly.
But like with welding, it can be hard to spot a less-than-optimal adhesive bond. By the time a screw is all the way in, you pretty much know if you got it right.

And everyone has the tools to insert a screw correctly. Not everyone has the tools or knowledge to prep, mix, and apply modern structural adhesives. Nor are they affordable for small projects. A better choice might be one of 3M's VHB tapes. Not cheap, but easy to use and pretty easy to tell if it's right or not. <Chas>

I googled VHB tape yesterday and this came up on the 3M page:

3M™ VHB™ Tapes are high-strength bonding tapes and a proven alternative to screws, rivets, welds and other mechanical fasteners.
Unlike screws or rivets – which join materials at a single point – high-strength bonding tape permanently adheres one substrate to another while spreading the stress load across the entire length of the joint. Once materials are joined with 3M™ VHB™ Tape a virtually indestructible “weld” is created.

It sounds like once pieces are joined by the tape, they can't be put asunder, i.e., you better get it aligned correctly because it can't come apart. Am I understanding this correctly?

Here is a link to a pdf with all the applications for each type of tape.
It looks like it bonds things like metals, plastics and glass. I don't see anything that implies that it works with wood, but the point was it would work with something like corplast, correct?

At some point in the past, I had bookmarked a link to Nida core honeycomb panels (used to build boats). There is a picture of a guy standing on one of the 2' x 4' panels with no deflection.
You can also get it in laminated panels.

Laminated Panels—Composite
These panels are constructed with Honey Comb sandwiched between two layers of either 18oz wet laminated glass, or 2.7mm of lauan. They are very rigid and can be used in a number of applications. Can be ordered in 4’ x 8’ sheets, and thicknesses from 3/8” to 1.” These laminates are NOT SCORED.

[Jack Olsen]

Yep. I've got two types of the VHB tape I'm testing this week. The 4900-series is supposed to be a possibility with the Coroplast/polypropylene sheets. The RP-series is supposed to be the right fit for aluminum composite panels. For redundancy (and better overall insulation/weather-sealing), I'll also line the aluminum composite panel seams with Dow-Corning 995 Silicone Structural Sealant, which could probably do the whole job on its own. (But in this case, I'm looking for both a belt and suspenders.)

My current thinking is to use L-shaped aluminum stock on both the inside and outside (as trim) joints of the whole box, with VHB/Dow-995 holding all the aluminum and aluminum-composite pieces together. I like the idea of no fasteners at all, but I will probably use them at the corners to prevent any kind of zipper effect under stress.

The coroplast/polypropylene-to-aluminum junctures are going to definitely get fasteners as well as adhesive. I'd like to build it to hold together even if all the plastic adhesive failed.

[aggie79]

This "fluted" or "corrugated" aluminum composite material used to make signs is very lightweight and already has the aluminum bonded to the core: http://www.nudo.com/p_alumacorr.php.

Sign shops cut it with CNC routers, so I'm assuming the aluminum skins make the cutting easier than a polypropylene only material.

[dales133]

Thanks for that tape link will come in handy.

[JuneBug]

Corplast related:

Saw an ORU folding kayak yesterday at REI -- made out of a corplast looking material.

[The] durable double-layered polypropylene material can be folded thousands of times without weakening; materials are extremely puncture-and abrasion resistant

but I can't find anything more detailed on the actual material used. As I'm going through their Web site, this seems to be a deliberate omission.
http://www.orukayak.com/


However, they do have a link to This very interesting article on the Maker Web site showing the entire process of manufacturing the boat and helpfully notes that

The body of kayak is made of one single sheet of white corrugated plastic.

[iregan]

Standard coroplast doesn't hold up well to uv over time. You might get 3 years out of it. While it can be handy stuff, its not as strong as foam, as light as foam, nor does it have a high insulating factor. You can always try roofing material like twinwall, used on greenhouses, but its expensive.
I think foam with the sign aluminum would work great, I even wonder about a frame made of a thinwall pipe, filled with expanding foam.
Regan

[Jack Olsen]

Today I did some gluing. I've been collecting material samples and different adhesives:



For the aluminum composite panels, I cut small test strips that I'll be able to stress test.



A lot of local steel pieces got recruited for clamping duty. Underneath it all are a bunch of combinations of EPS foam, XPS foam, corrugated plastic, aluminum composite panels and FRP panels. The sizes of the glued samples should be close enough to get relative weight data as well.



This is my thinking for a wall-to-roof joint. There is 3m VHB adhesive tape on both sides of both pieces of angle stock. I adhered it and then immediately cut through it with a band saw to see how it would hold up.



In actual use, the inside angle-stock will likely become 1" square tubing. The outside angle-stock will be trim. In addition to the VHB tape, I will also use sealing beads of Dow 995 structural adhesive.

I'm going to let the rest of the stuff cure for 24 hours and then do some testing.

Except for the bonds made with Dow 995, which looks to be a great adhesive -- but one that needs 1-2 weeks to fully cure.

[Jack Olsen]

My results could hardly be called scientific. But they're results. And some of them surprised me.

I made some little 4"x4" 'sample walls' so I could get a gut feel for strength and weight. Of course I can calculate the weights based on the material specs, but there's no substitute for holding something in your hand.

The 1" XPS (pink, Foamular) foam I got was denser than the thinner EPS (beer cooler) foam. There are denser and less-dense versions of both. But the XPS stuff can be cut with tools (whereas the EPS needs a hot knife or wire), and the XPS is nice and rigid. So I think that part of the decision is pretty easy, even if I went with thinner XPS.

The Aluminum Composite Panel I got has a white paint finish on it, to prep it for printing. I like this stuff. But if I can only get it with the white finish on it, I will have to cover it with a vinyl car wrap material that looks like brushed aluminum. On the one hand, this means I can repair scratches by replacing the vinyl. On the other hand, it adds more expense and might mean an additional prep step in adhering the stuff.

I got some beautiful FRP panel samples from Crane Composites, each with a woven wall pattern. They'd be nice for an interior, but I'll have to look at cost and weight as issues. Here you can see the interior finish, the white ACP finish, and the white ACP finish covered with the vinyl wrap that looks like aluminum.



And while you can see how I misaligned one little panel, this picture maybe shows the brushed aluminum pattern better:



An alternative for the inside is 4mm corrugated plastic. It's light and strong, but the corrugated pattern does show through, even if you cover it with a decorative vinyl. I might try to think of the pattern as a bonus, since it's significantly lighter than the FRP panel, and probably maybe better in terms of rigidity and strength.



Gorilla Glue (polyurethane based) was the surprise winner for adhering ACP (aluminum composite panels) to foam. It also did surprisingly well adhering ACP to itself. The Gorilla Glue Construction Adhesive (which doesn't foam/swell in the same way as the original glue) also surprised me, although it is not quite as good as the original stuff.

For adhering EPS foam and XPS foams to themselves, the unsurprising failure was Marine Goop, which dissolved the foams. Also surprising was the (relative) weakness of Shelby 277, which is a foam-specific adhesive. It worked, but not as well as either Gorilla original or Gorilla Construction. These are the samples after I did my best to tear them apart.





For the strip tests of corrugated plastic (to itself) and aluminum composite panel (to itself), my first thought was to see if each strip could hold a 110# anvil. As it happened, not even an unglued strip of corrugated plastic could support that weight, and I'm lucky I didn't crack a tile. This thing came down pretty hard.



But for the rest, I used a method of adding weight (from 26# to 36# to 46#) to try and get a failure. I took the ones that succeeded and rated them on how easily they peeled apart. For the corrugated plastic, the winner was (again) Gorilla Glue. Marine Goop worked, but revealed some damage to the plastic (and worries me about outgassing). Loctite Pro for Plastics was pretty good, but SuperGlue Plastic Fusion and JB Weld for Plastic both did worse than I expected. Both of them might benefit from woodpeckering holes into the surface, but that is extra work.



For the Aluminum Composite Panels, I think there might be a strong argument for abrading the surface if I can't get mill-finish sheets. The 3M VHB tape was less successful than I expected, although switching to a thinner (and less elastic) version of the tape will probably help. I also couldn't test my preferred method yet, since the Dow 995 adhesive needs a week to cure. I believe that a combination of (thinner) VHB tape and Dow 995 -- with better surface prep and the same cleaning -- will work for the structural bonds for this thing. But I'll know more in a week.

Gorilla Glue (again) surprised me with its ability to bond the ACP to itself. 3M ScotchWeld DP110 also passed with flying colors, although the peel results also pointed to the benefits of some ScotchBrite or fine sandpaper if I have to stay with the painted ACP.

All of this leads me to wonder a few things about Gorilla Glue. Its expanding properties seem manageable if I hang out and wipe the stuff as it emerges -- and maybe get more skilled at applying the right amount. But does anyone know if the expansion would cause problems over a whole 5x10 sheet? I'm wondering if it will push the panel out so that there is any bowing in the middle and general thickening if the expansion force doesn't have an easy escape route.

And does anyone know about potential health hazards from Gorilla Glue? I'd hate to subject my family to any outgassing hazards if I can avoid it.

[mikeschn]

I glued in some 4" wide by 48" long strips into the side of my foamie last weekend. I did note that when I dry fit it, it was really tight. I should have known better. When I glued it in, the glue expanded, and had no place to escape to. Consequently it pushed the wood out of it's slot. In the middle by as much as .125". You definitely need to give that glue a way to escape. Maybe cut slots into the foam so it can escape out the sides?

Mike...

[Fred Trout]

If I recall correctly, Glidden Gripper, a primer paint, did the best job in other tests gluing foam-panel-face to foam-panel-face, and metal to foam.

https://www.youtube.com/watch?v=rnOegaOKu38

Gluing large panel-faces with Gorilla glue is asking for trouble, imo, since the foaming expansion is uneven and irregular. You just do not want large panels glued to each other with an expanding foam unless you just glue where you can clamp with even pressure and provide a route for the foam to expandout of. Same thing with Great Stuff.

Gluing edges of a panel to another panel works well enough with GG or GS if you have a way to apply pressure to hold the pieces together.