Building Lightweight ???

[msybrant]

Hello all,
So I have decided to start building based on the Widget design with some stretch in the width and length. I'm towing with a Subaru Outback so weight is going to be an issue. I was planning on foam core walls with 1/8 plywood inside and out. Question one is has anyone ever used an expanding foam to fill cavities after the walls are framed (the same way SIP's are made). Question two is, are there other ways I can lose some weight before I start building. Also I want an Aluminum skin, question three is does aluminum come in 6'x10' or larger sheets and if not how do you go about the seams on the sides and roof and keep it watertight? Thanks.
Matt

[aggie79]

Here are some links to a wider, but shorter, Widget that came in around 1240#.

This is a link to the site - http://www.freewebs.com/kc8jwa/futurebuild.htm# (scroll down to "Widget Beginnings") and this is a link to the modified Widget drawings from the design library - http://www.freewebs.com/kc8jwa/widget7a.pdf.

If lightweight is a priority, you probably should forego the aluminum.

[msybrant]

Thanks for the links. I saw those when I was rooting around for ideas. I am set on the aluminum skin (looks soooo cool!). I was hoping for around 1200 lbs. I was wondering, for the roof would 1/8 plywood on the inside then foam insulation then the aluminum with no plywood under it work ok?

[BrwBier]

[quote="I was wondering, for the roof would 1/8 plywood on the inside then foam insulation then the aluminum with no plywood under it work ok?[/quote]
I can say that will absolutely work. I made mine like that several years ago and have had no problems.


Brwbier

[msybrant]

Brwbier,
Did you build your walls the same way? Does anyone have any input on the spray in foam like "great stuff" or a simalar product. I'm still trying to figure out seams in the aluminum skin as well. Thanks.
Matt

[AZSpyder]

Brwbier,
Did you build your walls the same way? Does anyone have any input on the spray in foam like "great stuff" or a simalar product. I'm still trying to figure out seams in the aluminum skin as well. Thanks.
Matt

I have been thinking of using it on my Puck project for the floor to skin sealing. Originally the factory sealed the area with tar. "Great Stuff" seems like a good idea. I sure am interested in if anyone found a bad side to it.

I used some to shape some sections on the nose of a Corvair I'm also working on. I did find it takes a few applications if you want it thick. I have some areas that are about three inches thick. I just sprayed it on that thick on a vertical area it flowed over after I walked away. Also if too thick it doesn't expand and harden in the center. It is VERY sticky and seems to adhere to everything, sticks very well to skin. I couldn't find anything that would take it off my hands except time and scraping. It can also be fiberglass over with polyester resin without melting. For the Corvair it carved and sanded well and fiber glassing worked for some custom shaping.

It is UV sensitive. Sunlight will darken it and seemed to make some test samples brittle over time. With the fantastic stick onto a surface and gap filling so far it looks like a good idea.

Jerry

[msybrant]

"Great Stuff" was just a suggestion. Any slow rise polyurethane expanding foam made for cavities is what I was actually thinking (tigerfoam). The construction technique is used for SIP's and prefab walls for houses. It should make a real strong wall for an RV with and r-value around 7 for a 1 inch wall. Just an idea. Any thoughts on the seams for the skin?

[BrwBier]

Yes, my walls are built the same way. I used spray foam as you can see to fill in around the pink foam board. In the curved sections I used two 1/2" pieces of foam board and in the flat walls I used 1"with the spray foam on the gaps. It made every thing very tight.
Brwbier

[Carter]

On the sides of mine I used 4x12 .030 and lapped them. Same on the roof/front/back with 4x8. Started at the bottom front and back and overlapped a couple of inches. In both cases I made sure the sheet at the top was overlapping the lower sheets.Put moldings over those seams also more to hold the aluminum than for sealing.

Many truck trailer repair facilities use 103" wide rolls to repair semi trailer roofs. I believe they make it in both white and mill finish. Would cut down on the seams. Not sure about cost

Pictures in my Album

[msybrant]

BrwBier,
Thanks for your answer. That is definitely what I was thinking and the foam board is a viable option if I cant figure out the spray foam.
Carter,
I saw your trailer in the hall of fame and it is BUETIFUL and is absolutely one of my inspirations. Thanks for your tip. Did you use anything between the two sheets in the overlap (adhesive or double sided membrane)?
Matt

[Carter]

Matt,
Nothing so fancy. I made sure that the edge of the overlapping sheet was over a stringer and went along that edge with a brad nailer. If I remember right I then put a bead of silicone caulk on the back of the molding covering the seam and brads.

On my build up sides I used Titebond where it was wood to wood and Liquid Nails from a gallon can for the foam to plywood adhesive. That's what Dow recommends for the pink rigid Home Depot type extruded foam. Applied it with one of those plastic serrated trowls. On my model airplane foam and balsa wings I use epoxy but that's a bit expensive and troublesome for a trailer. My sides are serious overkill with 2x2 and 2x4 framework with 1/4 ply" inside and out. That was before this forum started and gas was $2.50 and up. Now I would use 1x2 and 1x3 framing, 1/8" birch on the inside and 5mm water resistant Luan on the outside.

Jim

[Lou Park]

If you build your walls empty and then try to fill it with the expanding foam, your walls will bulge and come apart. Once there is nowhere for the foam to go, it will keep expanding, and blow out the walls. I have used this stuff on quite a few jobs and it can be brutal.
Lou