Various materials ranging from concrete to hard plastics have been used in constructing spas. Each material has its own characteristics in terms of spa shape, size, color and durability.
Gunite (air-blown concrete)–
Traditional, older spas and those built adjacent to swimming pools are frequently made of cement or gunite. In gunite construction, a webbing of steel reinforcing rods is used to conform to almost any shape or size of the spa. Most concrete and gunite spas have a band of ceramic tile rimming the spa at the water line to make cleaning easier. Some are completely lined with tile. The price of concrete and gunite spas depends on the size, location and difficulty of installation.
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.
Used mainly as a backing to strengthen acrylic and gelcoat spas, fiberglass can be either bonded or sprayed on the back of molded acrylic or gelcoat spa shells.
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.
Dense and non-porous, acrylic constructed spas provide a very hard, scratch-resistant surface that maintains its color and faith. Acrylic is available in various colors. However, because acrylic is not strong enough to stand on its own, it also requires fiberglass reinforcement.
Tough, sturdy and resistant to sun and chemical damages, and extreme temperatures, thermoplastic spas are noted for their strength, resistance to scratching and retention of colors. 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.
The portable spa can be installed in or out of doors, and usually fits through a standard doorway. A key advantage of the portable is that it can be taken with you when you move.
The Hot Tub
The original hot tub was an old wooden wine cask. Today, hot tubs are constructed in a similar fashion with constant soaking of the wood keeping the tub watertight without use of nails. The most popular wood used in the tub construction is redwood. Vertical grained all-heart redwood is strong, watertight, aesthetically pleasing and if properly maintained, will last for 15 years.
Other durable and usable hardwoods include cedar, cypress, oak and teak. The main characteristics that differentiate these woods are:
Redwood is extremely resistant to decay, does not splinter, and swells easily to watertightness.
Cedar comes close to resistant on all counts, except it may not be as long-lasting.
Cypress is very durable and resistant to alkalis, acids and other chemicals.
Oak, a hardwood, is extremely durable if maintained properly.
Teak is the most durable and decay-resistant of all, and has a natural oily smoothness. However, high price and availability may present drawbacks.
Hot tubs are usually four feet deep. While most are five to six feet in diameter, they can be as small as 3 1/2 feet in diameter or as long as 12 feet or more. A standard 5′ x 4′ tub holds 500 gallons of water and is generally comfortable for four adults. A 6′ x 4′ tub holds 700 gallons of water and is generally comfortable for six adults.