Owners of in-ground vinyl-liner pools tend to focus their attention on what is most visible — the enormous water barrier that covers the entire surface of the pool.
But the people who build the structures understand that what's under the vinyl is just as important to a successful pool installation.
There are several material choices when it comes to supporting a vinyl liner (after all, it's just a big bag of water, and anything with sufficient strength to hold up the sides for 20 or 30 years will do) and each has characteristics that have attracted a loyal following. A peek below the country's in-ground vinyl liners reveals steel, concrete, aluminum and plastic walls firmly in place. The arguments for their selection are just as solid.
Wood And Steel
Forty years ago, at the dawn of the vinyl-liner industry, many builders were using wood for the job. The boards were impregnated with salt, like pork, to keep them from rotting in the ground. "It was an earlier version of pressure-treated wood," remembers Fred Schall, senior vice president, Delair Group LLC, Delair, N.J.
Schall's experience in the industry reaches back to those early days when each new pool was invented from scratch. "They would build a pool wall that looked like house construction," he recalls, "with sills and headers, and they'd nail them together and put a liner in."
It sounds crazy today, but nobody back then had a better idea, and the scheme actually worked pretty well, says Schall. "You may laugh, but I've seen some of these wooden pools that were 30 years old."
At the same time, steel was presenting a good argument for vinyl-liner support with simple bendable sheet panels that were notched and brake-formed. Like today, they were a maximum of 8 feet long due to the fact that someone was going to have to carry them.
They held the lines on the sides well and did better than wood in the corners, but it was their manufacturability that sealed the deal in the marketplace.
"It went to steel because steel was easy to fabricate," says Schall. "There were a number of shops that started up making steel panels because it was so easy to do; you bought some galvanized sheet steel, and all you needed was a notching press and a brake to fold it. You could spot weld it or rivet it or whatever you wanted. They were very simple to make."
And so it was that steel came to dominate the vinyl-liner support industry. It has been the most popular wall structure material for in-ground pool kits for many years, and it retains the lion's share of the market today.
But there are several other materials that have strong adherents as well, including plastic, aluminum and even concrete.
A building material of choice for over 2,000 years, concrete is as attractive to today's pool builders as it was to the builders of the Colosseum.
Its strength is beyond dispute, and it's easy to shape as long as you observe a few rules and don't have a change of heart after the fact.
Of course, most concrete pools end up with a plaster finish instead of a vinyl liner. But for those builders who use a concrete base for a vinyl liner, the sand-and-cement mixture retains the same wonderful properties that make it popular for other jobs.
On the downside, the forms for pouring the walls have to be purchased up front, and they are not cheap. Forms may run six figures and up, so the money involved is a real commitment.
With the forms in hand, however, the material costs of building a vinyl-liner support structure are just rebar and concrete, which is relatively inexpensive and easy to transport to the jobsite with modern ready-mix trucks.
Once the pool walls are finished, the concrete pool has to be measured for the liner. This is a notable difference with steel, as most steel pools are computer-designed and cut to fairly tight tolerances, and their pre-ordered liners arrive with the panels.
Plastic And Sheet Metal
Plastic, or what is often called structural polymer, is quite as capable as concrete or metal, strength-wise, for the job. Plus, it boasts the advantage of being easier to carry.
Penguin Pools, of Milwaukee, uses both wall systems and usually bases the choice on the site conditions, according to Matt Rozeski, owner.
"It all depends," he says. "If we're building in rocky or really clay-filled areas we prefer steel. If it's sandy or 'normal dirt,' so to speak, we generally prefer polymer. The polymer walls use polymer stakes, the steel walls use steel stakes, and obviously with rocky soil or really hard clay, the steel goes through there nice and easy where the polymer gets hung up a bit."
Also entering into the decision between steel and plastic, he says, is the price of the polymer walls. He pays $600 more for them, give or take, depending on the size of the pool. And then there's the thought that must go through anyone's head as they contemplate a large pile of pool panels: The awkward-to-handle steel panels are 40 to 80 pounds, Rozeski estimates, while the polymer panels are about 20 pounds.
Of course, unlike metal, plastic does not rust, he notes. "When you dig that up in about 100 years, it's still going to look exactly the same, whereas steel is going to corrode." Not that a pool is expected to last a century, but if it does, the plastic can be expected to remain pristine, whereas steel and aluminum, in the moist ground, will degrade significantly.
Although both steel and aluminum offer the advantages of metal, steel is the much larger market. Schall believes his Delair Group is the only aluminum pool manufacturer in the United States. The main advantage of aluminum is that it provides good corrosion resistance in a panel that's easy to carry around. "Because aluminum is extremely light," Schall points out, "we can make panels that are 16 feet long. Two guys can easily pick them up, whereas two guys on an 8-foot steel panel is a grunt.
"So if you're building a 32-foot pool, we'll give them two 16-foot panels, and they'll only have one joint to work with. So it's faster and easier to build and align and level the pool."
Delair Group sells an aluminum panel with an electrostatic powder-coat to increase its corrosion protection. Such paint systems provide an even, baked-on finish that is remarkably durable.
It can still corrode, notes Schall, but with aluminum and certain kinds of steel, that can be a good thing, as the layer of oxidation provides a second barrier. Although it's not particularly attractive, accepting and even encouraging this protective layer of oxidation in certain types of metal is common practice in the construction industry.
For example, Schall says, "If you have an aluminum boat in saltwater, sometimes they just let the oxide form. You get an oxide layer about the thickness of a sheet of paper, and that protects the metal underneath it."
Boats And Pools
While there are sound reasons for building with concrete and aluminum, the high-altitude view of the U.S. market over the last 40 years would show a preponderance of steel, with a rising challenge from plastic over the last two decades or so.
As for the future, Rozeski says, that's hard to predict in the pool industry, partly due to an ingrained inertia. A lot of pool builders, he believes, are resistant to change. "They've been doing it the exact same way for 20 or 30 years. They're using the same distributor, the same equipment."
Rozeski thinks it takes a generational change to produce an industry change. "But as new builders come into the market," he says, "it's hard to say what they'll choose."
As a builder who uses both steel and plastic, he wonders if pool walls will follow the path of other products that have turned from steel to plastic.
"Years ago," he notes, "if you bought a boat, it was made out of steel or some type of metal. Now everything in the boating industry is plastic or carbon fiber or something like that. In pools, steel was used for years and years, but in the last 10 to 20 years, polymer is kind of the new kid on the block."
Scott Webb has been with AQUA magazine in one capacity or another since April 2001; he now serves as executive editor. Scott has a degree from University of Cincinnati in Aerospace Engineering and lives in Madison, Wisc.