Keep in mind that concrete and gunite spas must be custom designed and individually constructed and therefore are more time consuming and expensive to build. Also, note that installation is almost always included in the total price quoted by the contractor. A polymer resin sprayed onto a spa shell is allowed to harden then removed from the shell and sprayed with fiberglass for strength. Gelcoat fiberglass spas cost slightly less than acrylic fiberglass but are considered less durable. Gelcoat generally requires more routine maintenance and often needs resurfacing after about five years.
Acrylic is available in various colors.
However, because acrylic is not strong enough to stand on its own, it also requires fiberglass reinforcement. They are thicker and more resilient than acrylic and do not require fiberglass reinforcement. These plastics are also available in many colors as well as simulated marble. An addition to the spa industry is the portable spa. Constructed of fiberglass, often with an outer skirt of wood or other material, the portable model has heating, electrical, filtration and pump equipment within a self-contained unit.