Swimming Pool Gunite Construction
It is often frustrating in GUNITE Pool Construction to see rebound generated during a shoot, especially because pool builders get charged for it & have to pay for an expensive Gunite clean up.
If this is an area of concern, read on for some great tips on how to reduce Gunite rebound and wastage on your Swimming Pool Gunite construction.
Why is there rebound at all during a Gunite shoot?
Gunite, is essentially ‘Dry Mix’ Concrete. This mix is literally mixed with water seconds before it hits the application area such as the swimming pool wall. This mix is shot at almost 65 mph through a very high-pressure nozzle and the when material ‘bounces’ off from the wall rebound is generated. Without the Gunite mix hitting the walls with a VERY high pressure, the compaction needed to get the structural strength in Gunite will never be achieved.
So you can say some rebound is actually good as it shows the application has been done with appropriate high pressure.
We at United Gunite have regular training sessions from the American Shotcrete Association and per ASA a 15% rebound is to be expected from any Gunite shoot.
But having said that, there are Gunite shoots when the rebound is just excessive. Let’s delve into how to mitigate that.
| Lack of water pressure The water pressure feeding into the nozzle needs to be very high. Minimum recommended pressure is 65 PSI. Without this pressure the moisture content of the Gunite is going to be lower comprising the structural strength and also creating excessive rebound. |
| Shooting on dry surfaces Trained Nozzleman should be wetting the application area PRIOR to starting the Gunite application. The simple act of spraying water on the section being shot will yield a dramatic reduction in the rebound. |
| Incorrect sand mix Concrete primarily gets its strength from the Portland cement that is bonded ‘in between’ the space in the sand particles. Hence the importance of having the right sand mix to achieve low rebound but also high Gunite structural strength. As any experienced Gunite company will tell you, perfecting the sand mix used for Gunite is really an art form. But the technical ‘size’ of the sand that you’re looking for FM 2.5 to 2.6. This sand size is coarse enough to dry quickly but also fine enough to not have much rebound. At United Gunite we go to extreme lengths to ensure relationships with the right sand pits to source the right sand for our Gunite mix. |
| Incorrect Nozzle Designs A common mistake that we see old timer Nozzlemen make is to immediately cut the nozzle tip to get a ‘wider’ spray. This old technique has been debunked by the ASA because it reduces the pressure (& the strength) with which Gunite is being applied. Another recommendation is to upgrade the Nozzle with ‘teeth liners’. The material goes through the nozzle gun in a circular motion & having these stepped liners concentrates the material and reduces the rebound caused by wide sprays. |
| Incorrect Nozzle Designs A common mistake that we see old timer Nozzlemen make is to immediately cut the nozzle tip to get a ‘wider’ spray. This old technique has been debunked by the ASA because it reduces the pressure (& the strength) with which Gunite is being applied. Another recommendation is to upgrade the Nozzle with ‘teeth liners’. The material goes through the nozzle gun in a circular motion & having these stepped liners concentrates the material and reduces the rebound caused by wide sprays. |
| Not shooting Gunite in sections A lot of rebound occurs when Nozzlemen shoot Gunite on partially completed area. An example of this incorrect proactive is shooting one layer of Gunite on the pool walls and then coming back to finish the beams in that area. Compare to a correct application where one section is completely shot, followed by the Gunite finishers who ‘cut’ the application to finish elevations. This sectional shooting approach also makes the shoots more efficient since the work is staggered between the Nozzler and the finishers. At United Gunite we spend a lot of time training our teams to follow this approach and the results in reducing the rebound have been dramatic. |
| Call 713-730-2907 or Email office@unitedgunite.com to schedule your Gunite shoot with United Gunite |
Swimming Pool Gunite Construction by United Gunite.
Article Author: Steve Todd Lanni, United Gunite