• Andy G.

How the Variable Speed Pump Saved the Negative Edge / Vanishing Edge in Arizona



Negative Edge Pool

As a Phoenician, and a proud born and raised Arizona pool remodeling contractor. I have always been accustomed to the unique highs and lows of our beautiful Sonoran Desert. A geographic area with a "dry heat" that can reach 120+ Fahrenheit in the summer and below freezing in the winter. We are truly unique which allows long swim seasons and high / low daily temperature fluctuations between day and night.

With the 1990’s popularity of the negative edge (Otherwise known as - infinity edge, zero edge or vanishing edge) in the swimming pool industry, it set the bar for beauty. The look of a swimming pool vanishing off the edge of the pool surface is an elegant view unlike any we've seen in the pool industry.


Negative Edge with All Tile Spa

With the evolution of the negative edge, just like any evolving idea, it comes with engineering adjustments along the way. Whether to make the catch basin deeper or wider. Whether the slope and knife edge faced in our out. Whether the double reinforced steel barrier wall needed positive and negative sealing. These were all ideas and modifications that came with the evolution of the negative edge.

It seemed that these structural modifications when designed and constructed to plan would seem "fool proof". But there was always cracking, degrading, and deconstruction that would ensue. No one in the pool industry could guarantee the long-term integrity of the negative edge.


TIled Negative Edge Cracked and Popping

What was once the beacon of beauty in the industry became a maintenance nightmare that no licensed pool contractor would want to repair or own via the Registrar of Contractors. The money required to maintain the issues related with negative edges scaled beyond the look and feel it added to your pool dream.

With our unique dry weather, hard water and temperature fluctuations in Arizona, these negative edges have a lot of fluctuations to do themselves. As the heat rises, so does the surface temperature of exposed walls beyond the knife edge.


Negative Edge with Surface Cracks Attracting Calcium

As the negative edge cascades cool water over the knife edge to the exposed, hot negative wall via wind, swimming, or regular pump circulation schedule, it creates an environment of continual hot and cold fluctuation that in turn, creates thermal shock.

Thermal shock occurs when the temperature has an extreme temperature fluctuation in a short period of time which causes the pebble surface, tile surface, ledge stone surface and etc. to expand and contract. Eventually this expand and contract leads to micro cracking, lifting, and separation between the bond beam, and the surface which will eventually pop and fall off.


Negative Edge with Calcium Build Up and Cracking

To add to the thermal shock and cracking, our calcium build-up, which is extremely common to our desert in Arizona (Especially common in salt pools). As the surface cracks appear at a micro level, the water migrates into the cracks and eventually dries. This drying leaves calcium scale which builds up over time within the crack and causes the crack to enlarge and further popping and separation ensues. As our winter months roll in, that water that migrates within the cracks can freeze and further expand and pop these already vulnerable areas creating multiple variables of destruction.

Through the evolution, we gained knowledge of positive and negative sealing of the wall. This is done by sealing both the front and backside of the wall and that in turn would save the negative edge by eliminating the efflorescence of the shotcrete which led to the fall out of the backside of the negative edge. I would agree that this positive and negative sealing is very important, but what else can be applied to this obvious issue beyond what is beneath the surface?

THE ARRIVAL OF THE VARIABLE SPEED PUMP


Pentair Intellipro Variable Speed Pump

Let's retrace our steps. Temperature fluctuation from scorching to freezing, wet to dry moisture absorption and scaling, and crack penetration from calcification and thermal shock.

What can solve these issues? How about... now this may seem like a crazy idea, running the energy efficient pump 24/7 on low speed (equivalent to single speed 3 hours a day).


Negative Edge Exposed Pebble Popping

If I lost you there, hear me out. With the variable speed pump running at an energy efficient low speed, it runs quietly. It's not the worn bearings screaming from the single speed pump you're accustom to.

The constant cascading of the Variable Speed Pump will always maintain the negative edge wall's moisture and temperature. This eliminates thermal shock and calcium scaling. This keeps the negative edge wall consistent and eliminates wet / dry, hot / cold and combats calcium and mimics the attributes of your pebble surface under water. Because essentially, it’s always under a sheet of water while the pump is running.


Infinity Edge Spa with Variable Speed Pump Running 24/7

There is no perfect negative edge. We can only minimize the maintenance that comes with swimming pools, especially the swimming pools with negative edges. So, if I were to build my ultimate negative edge pool today, I would follow all steel engineering standards, seal both the positive and negative side with a Theroseal or other hydraulic sealing product. Install tile to the backside of the edge with a 6x6" ceramic tile for strength and minimized grout line. And finally, install the most energy efficient pump with a flow rate necessary for the size of my negative edge at the lowest speed available.

This would be the most preventative measures available today with the products and knowledge which has evolved up to now.

**This article is written from my experience in the Arizona pool remodeling industry. From a family business established in 1957 we have come across a vast amount of issues spanning decades. We specialize in providing solutions to the problems from the initial builds or the degradation the pool inherits over time.** – Andy Good –

Swimming Pool Service & Repair - www.Poolfix.com


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