So, I've been delayed on my house for 8 months by architect problems (first one did almost nothing for 3 months, fired him, took a month to find another, then he proceeded to do nothing too). But finally the work is getting underway.

I've written here before I think about my general plans, but now we've been working out the construction details. The home is to be underground, a series of cavelike domes (with large south-facing windows) connected with tunnels, with dirt and grass over the whole thing so that it just looks like a hill. The architect and concrete guy, after talking about it, decided that the easiest way to do it would be (for each dome) to have my excavator operator make a big pile of dirt, then build the form over it and pour, then remove the dirt. No problem, I figure the excavator operator can remove the bulk through the big opening for the windows and I can finish up with shovels in the areas that there'd be too much risk of damaging the concrete. Once the dirt is out, the plan is to go in with a high power pressure washer, not simply to remove any left-over dirt, but to remove the outer layers of cement, showing only the rock aggregate so that it truly looks like a cave.

I was also thinking about another thing. For most of the insulation, we were thinking about using pumice. Here in Iceland it's a renewable resource, the earth averages giving us many tens of millions of cubic meters per year ;) It also lasts forever, is cheap, and while heavier than foam is still quite light compared to sand/dirt/etc. It only has about a quarter the insulative value of foam at best, but there's no problem with piling it on thick.

Now, it occured to me: since we have to get large amounts of pumice anyway (enough to insulate the whole house), it should be able to fill up any one dome at any given time, I'd think. What if I had the excavator fill the dome-to-be with the pumice instead of dirt? One, it'd be easier to shovel out after the concrete is set because it's lighter, and two the concrete would be expected to bond with chunks of the pumice, yielding a surface that I'd think if anything would look even better than aggregate, and maybe not even need a pressure washing (although that's always an option).

But then something else occurred to me. Loose piles of materials have an angle of repose, wherein if they get any steeper, they collapse. Something like pumice probably can't get any steeper than 30 to 45 degrees. Of course, the constituents of dirt themselves are no better, but the different particle sizes help it pack better and moisture helps act like a glue, so it should be possible to build up steep sides.

What do you think, is my idea of using the pumice as the framework for the domes simply a no-go? Or can you think of any alternative ways to make it work? I mean, if it has to be dirt, so be it, it's not a big deal. :)