There are lots of "survival videos" on Youtube, showing "primitive" people making swimming pools in the middle of the forest. They always smear some sort of greyish material over the walls. Sometimes it's used as cement, like here, at 1:32. Other times, it seems to be used solely to seal the pool and prevent leakage, such as here at 11:36. It look like they are making some sort of cement.
How can an average person make this sort of cement? Is it mainly a certain soil, i.e. perhaps all these videos (from S.E. Asia) all have clay soil? Is it crushed-up rocks into dust, mixed with water? If so, would any sort of crumbly rock work or is it a specific rock? Do they add another ingredient (someone suggested they add ash, but I haven't found any video showing that). Is this cement able to used anywhere, or is it only effective on the sort of soil that they have in the videos?
More simply put: If people are camping out (in a forest environment), and they want to make a leak-proof ditch to store water (like a swimming pool), how could they make cement to seal the ditch using the resources found around them?
It should be noted that this is not discussing the legalities involved. Before actually doing this it is important to check with the relevant authorities and receive authorization, especially regarding public land.
