For years, I felt that part of the solution for explaining how the ancient Peruvians were able to have such close fitting stonework. I had suspected that they might have used an acid that could be obtains from boiling rhubarb leaves (or something similar).
Source
Gunnera Manicata is still found in Brazil and Columbia while slightly smaller G. masafuerae can be found close to Chile. Oxalic Acid can be prepared from these leaves which has a ph similar to sulphuric acid. Reversing the acidity could be achieved by mixing with a solution containing wood ash.
I had never considered that they might have used bags but in retrospect that would have been ideal. Reduce the rock to a pebbly paste using and acid and mixing in the alkaline solution to cure the "cement". Walls could be quickly erected and left to cure.