14 replies to this topic

[ntsqd]

As far as I know, yes it could be bonded on with Sikaflex before or after. Read up on what your bonding product of choice will bond to. I'd do so after a sealing coating of some sort, primer is porous, so I'd choose a bonding product that would adhere to whatever coating I chose. Might also look into the 3M VHB tapes as those are used to bond on the outer skins (& maybe more) of some of the really spendy diesel pusher RV's.

 

RV mfg's like Fleetwood don't weld the joints all the way around. They only weld on the interior to the wall surfaces. If they welded on the face surfaces they'd have to then grind every bead for the skins to lay smooth. Time is money to them.

 

For best R value I think a foam core construction is going to be hard to beat, but those don't deal with point loads very well. They take some thought and planning before starting.

 

For cabinet faces & doors I'd take a good look at Starboard.

 

I would also take a page from Rob Grey's Wothehellizat I/II builds and incorporate the framing for the interior features into the camper frame. Done well, more bonded (shear) panels, and the strength and rigidity of the frame will increase.

 

I've messed around some with designing a flat-bed camper and one design exercise that I haven't completely solved is the cold paths created by 'studs' that go from skin to skin. By using 1/2" X 1" tube for the 'studs' and offsetting them in two directions I've broken the cold path there. That forces the use of at least some 1/2" thick insulation or the cutting of notches in thicker insulation. Not sure that there is a fix for headers, footers, and around window openings. And I'm not sure if the gain is worth the added work.

 

One rather radical option that is worth considering is to build it entirely from wood. Build it like a boat where metal fasteners are rare rather than common. The cold paths created by the studs are not nearly as big of an issue. Weight can be quite low if well designed. The skin can be partially load bearing instead of simply a cover. If this intrigues I'll suggest finding some old copies of Wooden Boat magazine for research.

[Buckshott]

There is a relatively new (I think it's new) material being used by rv manufacturers as a substrate (replacing Luan) which they laminate the Filon to, it is called Azdel. They say it has some insulative properties, is impervious to moisture, and lighter & stronger than Luan.

​I don't think it would completely solve the "cold path" issue, but it may be a feasible way to minimize it? I talked with a 3M rep and they claim their (can't remember the exact name) contact cement used by rv manufacturing & repair shops will adhere to it.

Because of the point loading issue you bring up, I think I may be leaning towards a steel frame. One of my challenges will be to not "over-build" it, I am notorious for building things which end up too heavy.

Good conversation...

Thanks again!

[PaulT]

For cabinet faces & doors I'd take a good look at Starboard.

Starboard is used frequently on boats. There is quite a bit on my boat. There are some caveats to its use. First it is not light weight compared to wood products. Secondly, you are essentially limited to mechanical fasteners. Not many adhesives or sealants will stick to it unless there have been some advances since I looked for some a couple of years ago.

Paul

[Wandering Sagebrush]

Starboard is used frequently on boats. There is quite a bit on my boat. There are some caveats to its use. First it is not light weight compared to wood products. Secondly, you are essentially limited to mechanical fasteners. Not many adhesives or sealants will stick to it unless there have been some advances since I looked for some a couple of years ago.
Paul

I will reinforce what Paul said. Starboard is heavy. As it’s a slick material, even mechanical fasteners (screws) have a tendency to work loose, and it expands in sunlight/heat.

[ntsqd]

I knew about heavy, which is why I suggested looking at it rather than saying "it's the greatest stuff ever, use it!", but didn't know about the tendency for lag threads to work loose. Now noted.

 

Sounds like machine screws with nuts or thread inserts are the way to go with it. I use a lot of these at work to put threads into printed glass-filled nylon parts: https://www.mcmaster.com/92397a210