I recently came across some geopolymer / alkali activated material stuff on YouTube. Fascinating technology - you can in fact print a house or cast "liquid stone" into ceramic. Seems like companies are using it for expanding foam insulation now too.

The "natron hypothesis" seems to make more sense in Egypt where: Natron and granite powder are just laying around, the blocks are all regular rectangular shape, there are murals that seem to describe the process, and they have large high quality artifacts made from diorite which is the hardest thing around.

Of course that doesn't mean it was used everywhere in the ancient world, and this article does a great job discounting it for the Inca.

I'd love to know if there is some detailed microscopy and chemical analysis underway to see if geopolymer use can be proven in Egypt.