There's also "aircrete" which is basically foamed cement. Air bubbles take the places of stones and sand. > Foam concrete, also known as Lightweight Cellular

There's also "aircrete" which is basically foamed cement. Air bubbles take the places of stones and sand. > Foam concrete, also known as Lightweight Cellular Concrete (LCC), Low Density Cellular Concrete (LDCC), and other terms is defined as a cement-based slurry, with a minimum of 20% (per volume) foam entrained into the plastic mortar.[1] As mostly no coarse aggregate is used for production of foam concrete the correct term would be called mortar instead of concrete https://en.wikipedia.org/wiki/Aircrete https://en.wikipedia.org/wiki/Aircrete It's pretty crazy stuff. It's light enough that it floats on water, and it's waterproof. It's also fireproof, as well as bug-proof and mold- and mildew-resistant. It's very durable but you can work it with hand tools, saw it, drill it, etc. It takes nails. It's also a great insulator. There are folks who figured out how to make backyard-scale foamers for ~$100 of parts from any hardware store, and they make these beautiful aircrete dome homes: https://www.domegaia.com/ https://www.domegaia.com/ I've also seen companies that manufacture large aircrete bricks that are assembled onsite like giant LEGO blocks.