Concrete.

Concrete. Proportions 1: 3: 5, cement: sand: gravel, the thicker concrete, the better. The cement brand will be the one that will be in the store if it is smaller than the M300-400, add it more. Prepare concrete in a mini-concrete mixer, if any, manually in a trough, but it is better to order ready-made. During laying, pierce it with reinforcement to compact and release air until the surface of concrete moisturizes. Into concrete, when he grabs, we stick the reinforcement around the perimeter, the axis you are stretched. We knit the frame vertically, the thickness of the foundation should be larger.