you can buy this new stuff called coreflew, its foam injected plastic walls. a 50mm thick piece of it is the equivalent of a double brick wall, but is light enough to be lifted with one person. has better heat and sound insulation too.
its going to be the replacement for concrete tilt slabs/mdf/bricks etc etc.
its also fire retardent.
i'll try find some info on it for you guys, would be great to make a garage from it. it comes in heaps of sizes etc

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real men race downhill - keiichi tsuchiya