Lightweight walls

[tcolar]

What are the recommended techniques for building lightweight teardrop walls.

Thick plywood with parts removed and filled with insulation ... or maybe stick frame with aluminium for exterior and lightweight paneling on the inside (insulation in the middle)

Any links on walls constructions ?

Thanks.

[GPW]

TC , there are sooooo many ways to build a lightweight wall ... the two you suggest would work. Best read as much as you can on lightweights... Plenty of that here... Interesting reading too ...

[john]

In two builds I have used both methods you describe. I found the second method to be lighter.

The first build was a Tear Drop and a single piece of plywood for each side was all that was needed. I cut out what was not needed and filled the holes with Styrofoam.







My second build was larger and I chose to build up the walls to avoid splicing sheets of plywood together.

Instead of buying 1x3's for the "studs" between the 1/4" sheets of ply I ripped my own "studs" from a sheet of plywood mostly because it was half the price in total over the 1x3's (saved like $40), but there were other reasons.

--I wanted my "studs" to be only 1/2" thick so the hollow core of the walls would match the Styrofoam thickness.

--I wanted the total thickness of the walls to be 1" with the two 1/4" sheets factored in.

--I wanted to be able to vary the width of the "studs". In most places they were 1 1/2" wide. In some places like around the door, the curves near the roof, the area near the bottom and fender area they were wider.








In doing it again I would choose the second method due to its greater flexibility and lighter weight in the end.

Just my experience.

[angib]

I don't think using a hollowed-plywood core is a lightweight method, so I took John's photo and traced out the areas:



So that's 45% of the core that's still present. OK, this is a fairly extreme example, with the completely solid area alongside the galley, but other folks have left even bigger areas not cut out.

So that core plywood still weighs 45% of the full sheet - if it's made from 3/4" ply, it is about the same weight as a sheet of 3/8" ply with no cut-outs. So then add at least 1/8" either side for the skins and the sandwich weighs the same as a solid sheet of 5/8" ply. Other folk have just used a single piece of 1/2" ply - and that is actually lighter, as well as being much simpler.

The plywood core method does allow some insulation to be added, but when 45% of the area is solid ply with no insulation, is this really much of a benefit?

Stick-built sandwiches are definitely the way to go if you want a light wall (if you're not going to the ultimate of a bonded sandwich with foam core), but what you must do is minimise the width of the sticks. As a rule of thumb, I would say the sticks must not be much wider than they are thick, so nominal 1"x1" is OK and nominal 1"x3" is bad.

Incidentally, the stick width needed for structural strength is pretty small. If the sticks are wide enough to be a practical build method (like the 1x1 example) then they're much stronger than they need to be - with 1/8" ply skins, I think 1/8" ply webs on edge would be strong enough, though that would be near impossible to build.

Andrew

[Ageless]

Why not foam core with fiberglass? Very light and strong

[john]

Andrew:

Incidentally, the stick width needed for structural strength is pretty small. If the sticks are wide enough to be a practical build method (like the 1x1 example) then they're much stronger than they need to be - with 1/8" ply skins, I think 1/8" ply webs on edge would be strong enough, though that would be near impossible to build.

I felt I was pushing things with a stick "stud" width of 1 1/2". I was not. After building the walls (interior ply face down and gluing sticks/"studs" to join the pieces of ply together on the back) the strength was surprising. During building I was at first careful to lift the wall only while it was standing so as to avoid it failing along the joints. While moving it around alone a time or two I found that it could be lifted while laying on its side. The strength of the joint was amazing! I could have easily taken the sticks/"studs" down to 1" or less in width if all I had to worry with was the strength needed when the wall is upright.

[tcolar]

@John: Your trailer is so cool, I got two kids so it's kinda what I'm aiming for, although I will try a bit smaller.

You said your trailer is only 1200#, that's impressive, also I got confused when you said that was measured with a bathroom scale and bricks ???

@Andrew : What';s the "bonded sandwich" method ? how does it work ?

@Ageless : Is that painted on fiberglass ? How does that work, does that require special tools ? example of that construction link ?

Thanks again ... so many choices and decisions

[Larry C]

@John: Your trailer is so cool, I got two kids so it's kinda what I'm aiming for, although I will try a bit smaller.

You said your trailer is only 1200#, that's impressive, also I got confused when you said that was measured with a bathroom scale and bricks ???

@Andrew : What';s the "bonded sandwich" method ? how does it work ?

@Ageless : Is that painted on fiberglass ? How does that work, does that require special tools ? example of that construction link ?

Thanks again ... so many choices and decisions

Here's my take on what Andrew and Ageless are saying. Andrew and ageless may have better examples.....

I beleive what Andrew is refering to is a simple stick framing with foam insulation, fully glued between 2 layers of thin plywood (1/8"-1/4") Similar to what I have recently completed with my floor.

First skin glued and stapled to frame. Foam glued to first plywood skin and frame:




Plywood skins glued and stapled to inner framing and foam:



I beleive what Ageless is refering to is using fiberglass/epoxy directly over a foam core with minimul or no framing. Here's an example of fiberglass over plywood:

Fiberglass ready for epoxy:



After applying epoxy:

[GPW]

You can add tremendous strength to a stick -built frame by the addition of some simple gussets at high stress areas , as used on vintage aircraft...
A laminated TD profile with stick framing and gussets would be very light ... and still allow room for lots of insulation...

[Mini Renegade]

Im hoping to do the batton build on number 2. My chassis is an old and heavy caravan chassis I have been trying to figureout the best way to actually build it. I was thinking of halving joints to build the frame up before skinning the inside our outside. Reading what has been posted I will lay the inner skin flat and glue the framing to that with butt joints and steel angle plates and corner gussets where needed.

Thanks guys!

[afreegreek]

plywood this and particle board that.. bla bla..

there's many different types particle board just like there's many kinds of plywood.. saying particle board is crap just shows you don't know squat.. there is WATERPROOF particle board, as well as many different densities, glues, and wood fibres to choose from.. there's a few that would be just fine for building a TD out of.. and a few that are not.. just because it isn't at Home Depot doesn't mean it doesn't exist. try thinking outside the big box stores..

[angib]

What';s the "bonded sandwich" method ? how does it work?

It's the "foam core with fiberglass" that ageless mentioned but it can also be made with ply skins instead of fiberglass skins - indeed there's a good argument for preferring ply skins for light weight.

It is simply two thin surface skins bonded either side of a foam core - the foam core does the job of holding the two skins together that are done by the sticks in Larry's photos.

It is important to undertstand that a sandwich structure is nothing like a house - the sticks are not holding it up, the skins do that - the sticks just stop the thin skins from buckling and tie them together.

You can add tremendous strength to a stick -built frame by the addition of some simple gussets at high stress areas , as used on vintage aircraft...

I'm not 100% sure what you're proposing, but most gussets serve absolutely no purpose in a sandwich structure. In a teardrop, the skins are structural and provide way more shear strength than is needed for any load. That certainly wasn't true of vintage aeroplanes where the fabric skins had virtually no overall strength.

Again, the sticks don't hold up the structure - which is why they could be cut away to almost nothing. Of course we don't do that, because we want to do things like screw hinges into the sticks and screwing into the end grain of 1/8" plywood is neither easy, nor strong!

Roly will correctly point out that the door he used for his teardrop floor is an excellent example of a ply-faced sandwich structure that we use everyday. In this case the core is reduced to just a paper honeycomb, though with 'sticks' around the edge.

Andrew

[john]

@John: Your trailer is so cool, I got two kids so it's kinda what I'm aiming for, although I will try a bit smaller.

You said your trailer is only 1200#, that's impressive, also I got confused when you said that was measured with a bathroom scale and bricks ???

It's not 1200# any more. I filled it with perhaps 5000# of camping stuff.(I did not weigh the stuff )

A bathroom scale does not read high enough to weigh a camper. Although there might be a market for one these days, I have not seen one.

The brick/scale/2x4 method is just a way to get around the limitation of bathroom scales. The simplest to describe is where you mark the 2x4 into thirds. At one end under the 2x4 is the scale. At the other end under the 2x4 are the bricks to bring the 2x4 to the same height as the scale. On the middle mark sets a trailer tire. The reading should be 1/2 the actual weight therefore multiplying the reading by 2 would give the actual weight on that wheel. If the weight of the trailer is still to high for the bathroom scale to read dividing the 2x4 into fourths or fifths will lower the weight on the scale and you would have the appropriate number to multiply by to get the actual weight.

Add up the weights for each point that touches the ground and you have just weighed your 1200# camper with a scale that maxes out at 300#.

[Ageless]

Regardless of materials; once it all gets tied together; the structure becomes very strong due to the curve of the roof. A piece of 1/8" ply would bend easy if you walk on it, but once tied in to the structure it becomes very strong; likely I could stand on it.

Thanx Andrew for explain the foam core.

The simplest way to do it? You need a flat surface large enough for the panels. Lay out a sheet of plastic on said surface. Lay-up one side of the foam with cloth and resin; lay it down on the plastic; add weights and let it set up. Repeat for second side.

Now you have (2) walls. Depending upon the design; there would be several methods for roof construction.

[tcolar]

Thanks, seem s like the plywood skin sandwich method would probably work great for what I'm planning to do.