Negative ressure from the outside of a swimming pool is mostly attributed to blistering and bubbling of coatings after a period of time.
The building masonry in contact with the ground must be able to effectively counter the hydraulic thrust exerted by the water (both permanent and occasional forces) and protect the swimming pool from the moisture in the ground, again both permanent and occasional (caused, for example, by excavations or construction works that upset the hydrological balance of the soil). Precise intervention cycles are required to protect and waterproof the walls in contact with the ground.
Waterproofing to prevent negative thrust (or counterthrust) is performed on the surfaces opposite the side of infiltration, where the water tends to detach the waterproofing layer from the substrate. Typical applications for this type of intervention are walls (interior and exterior) of underground swimming pools. Instead, waterproofing to prevent positive thrust means treating the surfaces on the same side as the infiltration, countering the hydraulic thrust, guaranteeing water accumulation and sealing of the wall, preserving the wall of the pool from deterioration caused by the hydraulic thrust, by mechanical forces and atmospheric agents. Examples of applications for this type of intervention are structures used to contain water, even drinking water (basins, fountains, canals, conduits, tanks, swimming pools).