Concrete as a building material has been around for centuries and is made by combining small chunks of natural rock and a bonding material. In ancient times, the binding materials were things like clay or plaster, but in 1824 Joseph Aspdin invented what is known as Portland cement. Slightly adjusted versions of Portland cement are used by today’s concrete manufacturers and have been proven to stand the test of time for many years.

In swimming pool design, there are two main performance categories that must be met, regardless of which version of concrete is used, strength and tightness.

“cast-in-place” concrete

Cast-in-place concrete is what most people know as traditional concrete and is installed by constructing a form/frame and pouring the wet concrete mix into the form before smoothing the surface with tools such as trowels.

As the concrete dries, it hardens into a structure, as some of the water evaporates from the concrete. This act of evaporation causes the concrete to decrease in overall volume and can lead to cracks in the concrete. To minimize the risk of these cracks, when designing a concrete pool, engineers place joints in the concrete that absorb pressure changes that occur during the process.

However, this method of construction will result in the most consistent/smooth finish to the concrete, which is why many designers prefer it, but it is also the most expensive and labor-intensive method.

shotcrete

Shotcrete is a free-form method of applying concrete, allowing for more complex shapes and more impervious structures. It is applied by forcing the concrete mix under high pressure through a hose that is sprayed onto the surface. This method allows you to use a less water-dense concrete mix while maintaining the strength and waterproof nature of the structure.

The mix is ​​dry enough to spray directly onto pool walls with no casing required to hold it in place. This results in a stronger wall with fewer joints than the pour-in-place method and lessens the chance of future cracks and leaks. However, shotcrete generally leaves the rougher surface out of the three concrete pool construction methods.

By far, there are many less skilled shotcrete operators than standard concrete mixers, and as such, you must choose the correct pool builder for the job if using this method of construction. Failing to do so can have disastrous consequences.

gunite

The application of shotcrete is very similar to shotcrete in that it is applied by high-pressure hose and is free-form, but it differs in that no water is added to the concrete mix until the last minute. While shotcrete is pre-mixed before being pumped into the hose, gunite dries as it travels down the hose and is only mixed with water once it reaches the nozzle.

Due to this late mixing of water and concrete, Gunite has a lower volume of water in the mix than any of the other methods and as such is much less likely to crack and requires fewer joints. This is highly desirable for pool builders and because of this it is becoming an increasingly popular option.

As with Shotcrete, there are very few experienced Gunite application specialists and by choosing an inexperienced contractor you risk cracking or leaking later in the pool’s life.

None of these methods is perfect, and they all suit different situations, by far the most common method for concrete residential pools is cast-in-place concrete, but there has been a growing trend to use a combination of cast-in-place concrete. the place. spot for the floor and Gunite or Shotcrete for the walls to get the best of both worlds.