Okay, so the expanding foam experiment has not been an unqualified success...
Here are the styrofoam sections snugly clingfilm-wrapped to stop the expanding foam sticking to them - other than where I want it to stick: which is onto the surface of the original terrain boards, to form a bulk quantity of solid foam which I can carve to shape.
The 'lid' of the cave system will be applied to a film-wrapped section of board so that the underside is nice and flat...
Here's the can of expanding foam, nestling in a bucket of warm water...
If it's too cold when you apply it, it won't expand properly, so you need to make sure it's at a reasonable room temperature...
And here's the foam immediately after it has been used to 'ice' the board capping the cave system and to infill the gap between the end of the donga boards, and the front elevation of the new escarpment...
As you can see - first problem - one (very large can) does not actually hold that much foam. I've only managed to cover half the lid before the can ran dry
One hour later, and the foam has expanded to this...
That's a fair sized sausage of foam to carve into a slope... This part of the plan is looking good...
Another hour's curing time, and the foam hasn't actually expanded very much more. But I can now separate the sections of terrain...
Here you can see the insufficiency of the expanding foam lid. Looks like another can is called for... Bugger.
Here's the underside of the lid... Nice and flat, so that worked... Shame I didn't have enough foam
Six hours later... I decide to bisect the sausage, so I can work separately on the two halves of the donga terrain boards...
Second surprise: As you can see, after almost an entire day curing, the foam has still not gone off / fully expanded inside the centre of that sausage.
Less a satisfyingly solid expanded foam sausage - more of a Swiss roll with a gooey centre...
Another couple of hours and I set about cutting off the surplus expanded foam in order to start to shape the slope...
Although the central core of foam has still not expanded and looks a bit sick, it appears now to have dried in its unexpanded state... Hmmm...
Not that it really matters, because its role here is only to provide a lightweight bulk to build on with wall filler and surface texture...
Now however comes the big surprise...
As soon as I start handling the foam, it just falls off the board it is supposed to be stuck to!
Yes, that's right - all those dire warnings about 'this stuff will stick to anything and cannot be shifted' are utterly wrong.
Once cured, that nice shiny, rigid, plastic-like out skin it forms provides
absolutely no adhesion at all, not even to a coarsely textured terrain surface which ought to have plenty of grip for the material to key into. But no.
All is not lost, because of course the material fits exactly back on to contours of the board beneath. So I can easily skewer and glue the expanded foam lumps back into position, and then carry on carving to shape...
But...
I am now wondering of it wouldn't have been just as quick to use another slab of pink foam for the lid, carved down to shape.
And to have built up the slope using offcuts of pink foam as the underlying bulk material...
Ah well, you have to try these things, and only fair to showcase the, um.. learnings along the way
12 December 2012, 02:18:55 PM
