All in-ground pools have this in common: They must have some sort of watertight surface installed over the pool structure in order to hold water. Concrete pools use various types of watertight grout, fiberglass pools use a gelcoat and vinyl line pools use a vinyl liner. Underneath the vinyl liner there is an engineered structure to support the great pressure and weight of thousands of gallons of water, and to protect the pool from caving in from the ground forces pushing in. It’s because of these different types of structures that vinyl liner pools vary in cost, longevity and strength.
Wood to metals to composites
About forty to fifty years ago many liner pools were being built using various types of wood walls and sand bottoms. In the seventies and eighties, most pools were made out of galvanized steel and vermiculite or sand cement grout bottoms. Steel walls were easy and economical to manufacture and were strong and easy to install, but inherently would eventually rust and sometimes disintegrate, especially in areas with acidic ground and high water tables. Eventually the industry started looking into non corrosive pool systems like polymers and fiberglass. Fiberglass walls were the first non corrosive pool walls because they could be manufactured without a huge investment in expensive machinery and molds. As demand for in-ground pools increased and technology advanced, more and more manufacturers invested in the expensive machinery and equipment required to produce polymer pool walls and bracing.