Pitch

• While these areas seem level, driveways and patios have slopes to assist in water runoff. The pitch is usually away from the house, which is beneficial if the pool were to collapse suddenly; but a substantial pitch would risk collapse. If you want to pour a pad just for the pool, you can ensure that it is entirely flat and would be safe. If the slope is so tiny that the grade can hardly be measured, then it should be okay. However, the deeper the pool, the more the slope will affect the pool's stability.
  
  

Ground Cloth

• Intex recommends placing a ground cloth under all their pools no matter where they get installed. A ground cloth is a tarp made of a thick cloth instead of a plastic material. They keep grass from growing through the liner and prevent the bottom of the pool from rubbing against the concrete, creating holes. Concrete is extremely hard, and swimmers need to be careful that they do not fall and hit their heads while swimming.
  
  

Padding

• Permanent above-ground pools sometimes use a Styrofoam base, unrolled and placed under the pool as more protection from the concrete rubbing the liner. This is especially important during the installation, as someone has to go into the pool and use their feet to extend the liner and remove the wrinkles. Besides pool padding, indoor/outdoor carpeting or thick felt would keep the liner from rubbing the concrete.
  
  

Level

• If planning to install the pool over some form of ground covering, there are ways to level the concrete that are safe and secure. Sand is a popular choice for leveling because it goes under permanent aboveground pools. It is easy to work with and relatively inexpensive. However, sand will erode from under the pool in an uneven and potentially dangerous way. To use sand, you have to create a way to contain it, which is probably just as expensive as the pool. Your other option is to use the padding to build up the lower side. Remember that when the water is on the padding it will compress it, so add height to compensate.