Rob Gray of Australia has built the truck "Wothahellizat" twice - once used tape and then used glue to attach aluminum cladding to his steel frame - here is a link to his construction diary:
http://www.robgray.com/graynomad/wothahellizat/wot2/diaries/diary_19/index.php
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Fastening
Last time we used 3M VHB (Very High Bond) double sided tape to fasten the sheets.
It worked well but on Wothahellizat 2 we're using Sikaflex. There are a few reasons for this.
Firstly, when I was dismantling the old body I had a hell of a time removing the panels that were fixed with VHB but at least it was possible with hand tools. However the single panel that was glued on with Sikaflex (for reasons that escape me now) was impossible to remove manually. I had to rip it off with a fork lift.
Next there's the surface preparation. Unlike the standard double-sided (or "mirror") tape that's fairly thick and a little spongy, VHB is only 1mm thick and has no give at all. Therefore the surface has to be almost perfectly true or there will be gaps between the frame and the sheet.
This is difficult to achieve.
Sikaflex on the other hand can be globbed on in just about any thickness, so I don't have to grind every weld perfectly flat and I can adjust the thickness to ensure that adjoining sheets meet evenly.
VHB sticks instantly, you only get one chance to position the sheet. If you place the sheet and immediately realise it's not quite right you can remove it but you ruin the tape because half will stay on the frame and the other half will come away with the sheet. If you don't notice an error until after a few minutes during which time you've pressed the sheet home and maybe helped it along with a rubber mallet, bad luck, you'll ruin the sheet if you try to remove it.
Sikaflex on the other hand takes several minutes to go off, plenty of time to adjust the sheet's placement.
Using Sikaflex
Firstly, which Sikaflex to use? I asked several people, including some in the truck body building game, and they all said 227.
Then I looked on the Sika website, They state quite clearly that 252 is the recommended product for panels on truck bodies. I rang Sika here in Australia and got the same answer so that's what I'm using.
They also state that the area to be glued should be cleaned with their 205 cleaner and primed with 210 primer.
Now maybe they just want to sell more products, but I think it makes sense to follow the party line, so that's what I'm doing.
I apply the glue very liberally and try to ensure that just a little squeezes out from around the edge of the sheet. I then resist the urge to wipe the excess or clean up in any way, do this and you will spend the next half hour with black sticky crap everywhere, several rags stuck to your fingers, and a worse mess than you started with. Let it dry, it's easy to cut off with a knife.
Clamping. Sikaflex provides quite a good bond immediately, even a large sheet will stay in place and will not fall off the frame once it has touched the glue. So I find that minimal clamping is required, certainly you should not clamp too tightly as this will expunge the glue from the clamped area.
The sheet will however slide downwards and this has to be addressed, but not by clamping. With a large sheet I feel that the force required to hold it up by clamping alone is too great. Also you need to be able to rest the sheet in position several times while cutting and trimming it to shape. Therefore I feel that some simple support is required and I've made a few widgets that I can clamp to the body in various ways to provide "platforms" to rest the sheet on. These stay in place until I feel that the glue has set enough to support the sheet.
