Rebar, PSI and What a Pool Shell Is Really Made Of

The shell is the pool

Tile, coping, finish, lighting and equipment can all be replaced or upgraded down the road. The structural shell cannot, at least not without a huge job. Everything else in the backyard depends on that concrete shape holding its form through freeze and thaw, wet soil and decades of use.

That is why it is worth asking a builder two plain questions before you sign: what is the concrete mix, and what is the steel? The answers say a lot about how a company builds when no one is looking.

What shotcrete is

Shotcrete is concrete that is applied to a prepared form under pressure, rather than poured in from a chute. The crew excavates the pool, shapes the earth, ties a steel framework in place, and then the concrete is sprayed onto that framework to build the walls and floor. All American Custom Pools & Spas builds in-ground pools this way, and describes the shell step as applying the concrete under pressure.

You will hear the word gunite alongside shotcrete. In general terms, they are closely related methods of placing concrete with a hose, and a pool builder may use either word for the same type of shell. What matters more than the label is the mix, the steel and the workmanship behind them.

What PSI means

PSI stands for pounds per square inch, and for concrete it describes compressive strength: how much squeezing force a cured sample can take before it fails. A higher number means a stronger mix. It is measured by testing samples of concrete after they have had time to cure.

All American uses a 5000 to 6000 PSI concrete mix in all of its pools. The company says it chose a higher PSI mix to better withstand extreme winter weather, which is what a pool in Fairfield County or Westchester has to live through. This is a standard the company set for itself, and the numbers above come from its own published description of its work.

Why rebar size matters

Concrete is strong when it is squeezed and comparatively weak when it is pulled or bent. Steel reinforcing bar, or rebar, is what gives the shell its ability to resist those other forces. The rebar is tied into a cage that follows the shape of the pool, and the concrete is then built around it.

The size of the bar is a basic choice. The industry standard calls for 3/8 inch rebar, and All American uses 1/2 inch rebar to build the frame of its pools, for added stability and strength. A heavier bar is a decision about what the pool is made of. You can't see it once the shell is finished, which is exactly why it is worth asking about before the job starts.

• Concrete mix: 5000 to 6000 PSI in every pool.
• Reinforcement: 1/2 inch rebar for the frame, where 3/8 inch is the industry norm.
• Placement: concrete applied under pressure to a prepared steel framework.
• Equipment: owned by the company and kept in its own 25,000 square foot warehouse and office facility.

What the warranty says about the shell

A builder's confidence shows up in the warranty. All American backs the pool shell with a Lifetime Structural Warranty, and the pool equipment, including pumps, heaters, chlorinators and filters, with a 3 Year Parts and Labor Warranty. The company states that the conditions of both are available before sale.

That last point is worth acting on. Ask to read the conditions before you sign anything, from any builder. A warranty is only as useful as its terms, and the time to find out what they say is before the contract, not after a problem.

Questions worth asking any builder

You don't need to be an engineer to compare bids. Ask what PSI the concrete mix is, what size rebar goes in the frame, and who owns and services the equipment. Then ask how the shell is warranted and if you can see the conditions in writing.

The case study the company publishes shows why it matters. A Greenwich pool was built above grade inside a raised patio, with a concrete footing vault supporting the structural enclosure. Details like that depend on a shell that was designed and built to carry the load.

If you would like to see how All American builds, call (203) 433-6808 or book a design meeting at the Bridgeport showroom. You can bring your questions about concrete and steel and get plain answers.