The required thickness of concrete for pool walls depends primarily upon the state of the soil. Soft, sandy soils will require thicker walls than hard, rocky soils in order to ensure the stability and integrity of your pool. To reinforce the structure of the pool, the walls are usually made at least 6 inches thick. They can be even broader, noting that the plaster finish of the inside should be a minimum of 1 cm thick. It is important to discuss this with your pool builder, as they will be able to provide recommendations based on the specific requirements of your project.