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Gunite vs. Shotcrete

The debate continues...Which is best: shotcrete or gunite?

Keywords: Shotcrete, gunite, concrete sprayed concrete, cement

The question of whether gunite is better than shotcrete depends on a number of factors. Each process has its pros and cons; I hope this article will help to explain things so you can decide which is better for your pool construction.

It is true, just like any number of other types of materials, there are those who rely heavily on gunite over shotcrete and vice versa, even if it is not the best in the situation. Even highly trained and solidly educated contractors can get lulled into a comfortable rut, never switching to the other, even when it is called for. Each material or process requires specialized equipment and training so the learning curve for each can be a long one.

Gunite and shotcrete are both applied in much the same way; however, there are subtle differences in the general makeup of both materials, but mostly it is the application that varies.  Both are cement, sand and aggregate mixes (concrete), but it is how they are mixed and shot out that is different.

Gunite and shotcrete are both force applied concrete applications and shot at sprayed or blasted onto a surface.

Descriptions:

Gunite is cement, mostly sand and small aggregate (concrete) shot through a hose in it's dry form and then mixed with water at the end of the nozzle on the jobsite.

Shotcrete is pre-mixed concrete pumped in its wet form through a hose and sprayed, shot or blasted onto a surface.

With both types of applications, the skill of the operator is just as important as the choice of the material being used.

Ray Alderete from Alderete Pools of Orange County CA, an experienced custom pool designer builder in Orange County Ca. has over 40 years of swimming pool design and building experience and uses gunite to create luxury pools for his clients. He says:
"If the operator is not operating the hose and nozzle correctly, there will not only be problems with waste, but other potentially damaging issues to consider as well. For vertical or overhead applications, the major concern is rebounding where the material will bounce back off of the surface it is being applied to, and fall to the ground. In a swimming pool, this material must be cleaned off and removed or it will create weaker portions in the floor. These weakened areas can then lead to cracking and other damages that will mean costly repairs for the homeowner in only a short period of time."

Gunite and shotcrete terminology is often used interchangeably; however, this is not accurate as they are different. Shotcrete uses concrete or aggregate to give it additional strength; this does not mean that it is necessarily stronger or better. Gunite is the original term that was used for the material that was developed, however other companies who use a similar material or similar process may use different terms for their product. Gunite today refers to the dry mix process with the name coming from the way that it was applied, in this case, from a high pressure gun.

In either case, the ability to reinforce the sprayed material with metal rods, steel mesh or fiber mesh is a real consideration and should be evaluated for need in applications involving slopes or tunneling of any kind. Some deeper pools may benefit from reinforcements of various materials as well.

According to Alderete, "Gunite is typically described as the faster setting, stronger of the two material types and is considered to be the best material to be used for swimming pools and similar applications. "Because gunite is a dry mix and the water is added at the end of the hose nozzle, it gives complete control to the applicator. Gunite applicators can adjust the mix and make it as dry or wet as they want or need. By reducing the water content you can make the material stick better which is great for walls, waterfalls, and vertical applications. Since gunite is moving at a high velocity as it comes out of the hose, this can result in a higher PSI (pounds per square inch) application, packing material tighter than shotcrete could ever do. By reducing water in concrete it makes it even stronger so you can ulitmately achieve a very strong concrete pool. In either case, the ability to reinforce the sprayed material with metal rods, steel mesh or fiber mesh is a real consideration and should be evaluated for need in applications involving slopes or tunneling of any kind. Some deeper pools may benefit from reinforcements of various materials as well.