All About Concrete (Gunite, Shotcrete) Swimming Pools
Concrete is the most traditional type of swimming pool and arguably the most popular type of pool. Concrete pools offer the most customization as they can be designed in any shape or size. They also provide homeowners many choices for finishes.
While we call this type of pool “concrete,” concrete pools are no longer built with poured concrete and wooden forms or molds or concrete blocks. Today nearly all professional builders create a “concrete” swimming pool by using steel-reinforced rebar is installed along the sides and bottom of the hole to create a basket-like mold that will make the shape and depth of the pool. After the mold has been completed, gunite or shotcrete is sprayed into this form.
Both gunite and shotcrete are equally strong and are composed of cementing materials. Interestingly, gunite and shotcrete are also stronger pounds per square inch (psi) than poured concrete. Many people use “gunite” and “shotcrete” interchangeably to imply the method of spraying concrete. The big difference between gunite and shotcrete is their compositions when they are applied to the mold. Gunite is considered “dry” concrete, and shotcrete is considered “wet” concrete. When the gunite is applied, it is mixed with water in a special installer hose. When shotcrete is applied, it is already wet and is mixed with compressed air.
This beautiful concrete pool was designed and built by our NPC Premium Member, Concept Pools, LLC. Learn more about this builder.
The Two Primary Phases of Constructing a Concrete Pool
A gunite pool’s construction can easily be divided into two major phases: what happens before the concrete (gunite or shotcrete) is applied and what happens afterward.
Before the Gunite is Applied
As you might imagine, the first step to building a pool is digging a hole in the eventual pool’s basic shape and size. The following (also obvious) step is to remove the rocks, dirt, and debris (excavation phase) from the dig. The next step is the plumbing. The contractor or a plumber will lay the pipes needed for the pool to function correctly. These pipes will run inside the pool along the floor and walls and are necessary for drains, skimmers, and returns. After this step, some contractors will place a layer of gravel on the bottom of the hole. After the hole is dug correctly, excavated, and the plumbing has been laid, the contractor will install the steel rebar. The rebar is laid on the bottom and walls of the hole and resembles a grid or basket. Stronger rebar is usually installed at the pool’s top to help support the concrete that reinforces the coping and deck. Bars that cross one another are held together with heavy-duty wire, and eventually, a basket-like form takes the shape and size of the swimming pool. Besides the pool’s size and shape, other considerations like soil can determine how many bars are used and how close they are placed. After the rebar has been installed, an electrician grounds the steel and installs any pool lighting and fixtures. All the metal used for your pool must be properly grounded, including filters, pumps, heaters, slides, and ladders. After all of these steps have been completed, the gunite is applied to the form.
After the Gunite is Applied
After the gunite is applied and before it cures, the builder will trowel the surface. Then the coping is installed. Coping is the “lip” or the piece of concrete at the top of the pool that slightly hangs over the pool’s top. Coping is installed to help water drain away from the pool and is the piece of concrete that attaches to the pool’s wall and the deck (with a waterproof movement joint). After the gunite cures (dries), it’s time to add your finishes.
Pool Finishes for Concrete Pools
After the shotcrete fully dries (or has “cured”), another surface is applied over the concrete. This surface is the visible top layer of the swimming pool. There are multiple looks to choose from, but the two most common surfaces are plaster and aggregate finishes. Each type of finish varies in price, but plaster is the most economical.
A Standard Plaster Finish
Plaster finishes are applied by a professional with a trowel. The most common plaster finish is white. Plaster finishes can also be colored, but the color often fades or changes over time. When there are chemical imbalances in the water, plaster finishes are vulnerable to changes like stains and even cracks. The pool must be filled while the plaster is not completely dry. Follow best practices to avoid damaging the plaster during this stage.
Aggregate Finishes
Quartz, pebble, and glass beads are the most common types of materials used in aggregate finishes. Aggregate finishes are created by mixing plaster with pulverized quartz stone, tiny polished pebbles, or glass beads. When the plaster starts to cure, a professional applies water using special nozzles and strips the plaster’s top layer to expose the material mixed with the plaster.
Generally, aggregate finishes are smooth and increase the surface’s durability. Most quartz finishes show flecks of color (think quartz countertops), while pebble and glass finishes are more textured and typically make up most of the surface area with little plaster showing. Aggregate finishes are considered less susceptible to chemical imbalances.
When selecting your finish, don’t forget to ask your builder or plasterer for the surface’s life expectancy and the manufacturer’s warranty.
Above the Water Line and Tile
You’ve probably noticed that most concrete pools have one or several rows of tile above the waterline. The tile usually fills the area from the water line to the coping. Coping is the topmost edge or lip on the pool and is the piece that is placed between the pool wall and decking. While the tile is an essential decorative element, it plays another, more functional role by keeping the plaster below water, allowing it to cure correctly. Since tile is easier to clean than plaster, it helps keep your pool cleaner and prevents algae growth. Visit the blog >>