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I have been to Tiahuanaco/Puma Punku. Some of the andesite blocks do have a curious surface appearance. The idea these blocks, or elsewhere like Egypt, were in fact "cast" like cement is bunk on several levels. In Peru and Bolivia at least, however, I have seen enough that does make me open to the idea they were able to manipulate stone with some kind of heat more than likely the result of a chemical reaction. If you look at enough of the H-blocks in particular, some have rough surfaces and others are smooth giving the impression the rough blocks were not completed. It seems to me these blocks were roughed out using tools and made smooth by perhaps this chemical process.
As an aside, some of the sandstone blocks at Puma Punku (and Tiahuanaco) are absolutely massive. This struck me as a disconnect with the H-blocks and other similar stone working giving me the impression the sandstone blocks were from a different era.