https://youtu.be/Vv49DND3uPI

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).  
![](https://steemitimages.com/DQmZT6Giib5NMYCLqoWt5YJUQsZLBEpxgCtRtptipLgDtnX/image.png)
[Source](https://www.gardensonline.com.au/GardenShed/PlantFinder/Show_1722.aspx)
_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.