In the pool industry, there are two kinds of concrete. Wet mix and dry mix. Wet mix is often called “Shotcrete.” The dry mix is commonly referred to as “Gunite.” The difference here is simple but very important.
Concrete is made up of 3 basic ingredients – Sand, cement, and water. With Shotcrete, the water, sand, and cement are all pre-measured precisely at the factory. And it’s monitored as it’s poured into the truck. The concrete that is used to build your pool is exactly the same, every time.
Gunite, on the other hand, is a whole different animal. It’s manually mixed on the spot. The ratio of sand and cement is adjusted by whoever happens to be working the truck that day. And the water is controlled by another guy who usually can’t even see the truck.
The person spraying the gunite has two triggers on the spray nozzle: one for water, and one for dry mix. They can add as much or as little water as they think is right. How do they know how much is right? Basically trial and error. (You just hope the error isn’t on YOUR pool.)
Here’s another problem with Gunite that Shotcrete doesn’t have. It’s a thing called “rebound.” The only gunite that is considered “usable” is the part that sticks to the frame the moment it’s sprayed. Anything that falls off and hits the ground is called “rebound.” If you try to use this “rebound” material, you will form a “cold joint” which has a significantly higher probability of failure.
REBOUND is considered SCRAP, and should NEVER be used in any construction.
Unfortunately, not everyone knows that all rebound should be scrapped. (Or perhaps more accurately – not everyone DOES that.) In fact, it’s not at all unusual to see Gunite workers scoop up gobs of rebound “waste,” and use it to make steps, benches, fill in holes, etc. (After all, it saves them time and money on concrete, right?) But these “cold joints” that are formed with the “rebound” can cause all kinds of trouble down the road. From tile lifting, to hairline cracks, to a complete failure of the shell – These problems are often a result of trying to reuse “gunite rebound.”
With Shotcrete, THERE IS NO REBOUND, so this problem simply cannot occur. Shotcrete also happens to be substantially harder than Gunite. (Ask anyone who does repair work on pools.) Gunite is easy to drill through. Shotcrete is hard as a rock. That’s why at Bluewater pools, we prefer Shotcrete over Gunite for OUR pools.