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.

  • 2
    If this is on public land, or on land that belongs to other people, then you shouldn't be doing this. Even if it's on your own land, it may be illegal for you to dam a creek.
    – user2169
    Apr 13, 2021 at 12:41
  • @BenCrowell you are right, I had not addressed the legalities involved. I edited the question to reflect this. (I had discussed this idea with a friend, who owns large swaths of land in the outback of USA so it wouldn't be a problem. And he was planning on just letting it be left an artificial lake/ swimming pool filled by rain water on his property. But as a general question I should have initially given the caveat.)
    – Binyomin
    Apr 13, 2021 at 13:20

1 Answer 1


It is simply just clay. Clay is very water-impermeable in general. This is the reason unfired and unglazed pots can be used to hold water. Some of the water will be absorbed by the clay, but this is a slow process, and will generally only affect a shallow layer on the surface for the short times shown in the videos.

  • 1
    This is exactly how the first canals were made watertight - the process is known as puddling. May 13, 2021 at 15:33
  • @TobySpeight - that's awesome
    – bob1
    May 13, 2021 at 23:22

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