Paquette Pools and Spas
There is a common debate among builders of vinyl-liner pools: Polymer or steel walls? But there may be an even more important argument to be had.
“The fact is there is more square footage on the bottom of the pool than anywhere else,” says Mike Giovanone, owner of Concord Pools in Latham, N.Y.
So perhaps more thought should be given to the materials builders use when laying the floor. This comes down to two main options: Concrete and vermiculite. Each has its pros and cons. Here, builders discuss their preferred choices.
Let the new debate begin.
Concrete
If the objective is to create a solid floor impervious to the elements, accept no substitute.
Unlike vermiculite, its porous counterpart, concrete keeps groundwater at bay — no more floating liner. And liner replacements aren’t complicated by floor repairs, which can be extensive given vermiculite’s tendency to dent and spoil.
“You solve all your water problems, liner-change problems, footprints, heel marks — anything inherit to a vinyl-liner pool,” Giovanone says. He leads a boot camp for Latham Pool Products, training dozens of dealers every year on concrete techniques.
To his mind, to build a vinyl-liner pool with anything less than concrete is folly.
“You would never pour benches or stairs with vermiculite. Why on earth would you pour a floor with vermiculite?” he asks.
Of course, concrete should be approached with caution. There is a learning curve, but Giovanone says it can be easily mastered. You just need to work with the right concrete mix.
Giovanone has devised his own special blend over years of experimentation. It has a structural value of 3,800 psi and is mixed with mason sand and high fly ash content, giving it a frothy texture. He refers to this mix as “pool whip.” This makes it easy to trowel to a mirror-smooth finish. That’s why he likens his mix to vermiculite’s airy composition.
“It’s the same process, but a different product,” he says. “If you gave some of my top guys a load of regular concrete, they’d quit on me.”
To be sure, this is not the same heavy, laden material used to make porches and sidewalks. The fly ash gives it a blotchy appearance.
If you decide to go this route, give careful consideration to the aggregate in the mix, he advises. You want crushed aggregate consisting of stone sizes between ½ inch and 2 inches. A variety of sizes creates a stronger matrix.
“If you’re using all [1- or 2 inch stone], they’re not going to interface as tightly when you mix them,” Giovanone says.
He cautions against round stone. “You’re going to put round stone on a 45 degree wall, and it’s going to want to roll,” he says. “I’ve had people tell me, ‘I’ve been putting in concrete with round stone for years,’” and I say ‘Well, you’ve been working too hard, son.’”
In contrast, crushed stone will interlock with each other, securing the walls in place. Plus, it’s easier to trowel.
Giovanone’s process does not require rebar. But at a couple of inches thick, a concrete bottom comprising a strong mix should hold up under the weight of tens of thousands of gallons of water, he says. And if the earth below the floor caves or settles, the concrete shouldn’t be affected. On the other hand, even proponents of vermiculite acknowledge that their preferred material is subject to shift, crack or cave due to the ground settling. (However, they maintain that vermiculite repairs are much easier to make.)
Matt Rozeski made the switch to concrete several years ago after taking Giovanone’s course. He hasn’t looked back since. The owner of Penguin Pools, with locations in Waukesha, Wis. and Minneapolis, says one of the biggest adjustments to make was speed. Concrete sets faster, necessitating that his crew trowel quicker. But this has an advantage: He can install a concrete bottom in about half a day, whereas vermiculite can take eight-plus hours to cure, provided there is no rain.
Concrete is cheaper than vermiculite and more efficient. Because it is delivered already mixed, there are no dust or bags, making clean up a snap. Plus, Rozeski believes he’s giving his customers a better product.
“This is what distinguishes us from other builders,” he says.
Note: Giovanone’s blend is readily available. You just need to specify the formula to your local supplier.
Vermiculite
Vermiculite is a lightweight mineral. Mixed with Portland cement, it forms a semi-hard surface that feels slightly spongy underfoot.
Many of the arguments against vermiculite are same reasons some builders favor the material. Because it is porous, it won’t trap water between the floor and liner. The liner may float, but it will recede in time.
As with concrete, crews should make the vermiculite layer between 1 and 2 inches thick. Any thicker and it will void the porosity, which would defeat its purpose.
Fans of this material also claim that it’s easier on the liner. Vinyl expands and contracts with the temperature. The constant shifting back and forth on a rough concrete floor would, they say, reduce the liner’s lifespan.
And because vermiculite takes longer to set, you can be more meticulous. Any imperfections can be addressed later. It can take one to two days for it to cure.
“We usually have a crew of four guys spending half a day putting the floor in. Then, the next day, we’ll send guys to spend a few more hours on it to fine tune it,” says Dan Lenz, vice president of All Seasons Pools and Spas in Oak Park, Ill. “Because it is soft you can shave the ridges off easily.”
This is important, because pool lights will reveal all the imperfections under the liner. Lenz recalls a minor eyesore in the pool that he had lived with for years. When it came time to replace the liner, he was easily able to file down the blemish. Concrete, on the other hand, would require a grinder and no small amount of skill and experience.
Proponents of the mineral mix say that the ability to quickly patch problem spots is the material’s main advantage over concrete. New vermiculite bonds to old vermiculite well.
When doing a liner replacement, floor fixes are common. Frank Christiana, president of The Liner Specialists in Carmel, N.Y., will offer a ½-inch topcoat of vermiculite over the entire bottom if it requires extensive repairs.
“You’re getting a consistent layer where there aren’t any peaks and valleys,” Christiana says.
Vermiculite advocates also tout a greater sense of control. It’s mixed on site. The advantage here is that you can control the pace at which the material is made. Lenz uses a gravity feed mixer, which dispenses the vermiculite through a hose at the bottom of the pool as needed.
A concrete truck isn’t going to be patient.
“They’re accustomed to doing sidewalks and driveways, so they dump it quick,” Lenz says. “A pool requires a little more time.”
If vermiculite has one major drawback it’s this: The material can breed algae, which can bleed through to the other side of the liner. That’s why it may be necessary to shock the floor when replacing a liner.
Builders who prefer this material also acknowledge that the floor can cave in spots where the ground settles under the floor. But then again, concrete can crack and flake. Neither material is immune to problems.