How to make plaster for a pool floor ?

[asafyi]

I dug a hole in my backyard about 1.5mX1.5m currently about half a meter depth, hoping to make it something like meter and a half.

I intend to use some concrete as a floor and to make some plaster in order to prevent the water from leaking.

My intention is to cover the walls and floor of the hole with concrete and a thick layer of plaster on it

I need a recipe for plaster - how to make it and how to use it.

thanks ahead :-)

I have some pictures but I can't post URLs on public, so please contact me in private message.
TY very much !