A hundred years ago, Americans knew pools as intriguing public attractions, usually located by the seashore or over natural springs. Great places to socialize, they also provided one of the few ways to escape the summer heat before the invention of air conditioning.

Families — extremely wealthy ones — began owning their own pools in this century’s early decades, making pool ownership a symbol of the good life. By the 1920s, Hollywood publicity machines had picked up on this image and reinforced it by having movie stars pose beside their own pools. It took status and glamour to swim alone — and movie stars had both.

Southern California pool construction averaged about 20 pool starts a year through the ’20s, with half of those clients coming from the movie industry. Designers modeled many of the pools after the reflecting pools and channels found in traditional European gardens. They generally cost $5,000 to $10,000 in 1920s dollars, and were paid for in cash. The typical $5,000 model measured about 20 by 40 feet and came with a galvanized ladder. Tile trim, chromium-plated brass ladders and springboards came in the deluxe versions.

Early builders such as Pascal Paddock, Lawrence A. Cline, Philip Ilsley and E.L. Wagner hailed from such well-established industries as landscape architecture, construction and water treatment. Recognizing a niche in building pools that could be quite profitable, they started the nation’s first exclusive pool-  construction businesses, catering to municipalities, millionaires and celebrities.

An engineering graduate, Paddock opened the first of these firms in Southern California, leading some to call him the father of the pool industry. For his company, pool construction began as an offshoot of such related work as building concrete structures for tennis courts and retaining walls, and designing sewage systems and municipal waterworks.

Pools didn’t evolve much in the ’20s. Unable to bend forms for radiuses and coves, builders shaped rectangular pools with straight, vertical walls that met perfectly flat floors. To build them, crews formed and poured concrete using two curtains of square (rather than deformed) steel rods as reinforcements. Other contractors built the walls with concrete block — another barrier to creating curves.

In California, the walls measured about 8 inches thick, while pool walls on the East Coast generally measured approximately 12 inches thick to withstand freezing temperatures. Lights at this time were strictly dry-niche, located either outside the pool or in a wall above the waterline.

Early pool construction was extremely labor-intensive, with crews preparing for the pour with two complete sets of forms — on the front and back of the walls. Many crews hand dug their pools, especially the tough-to-reach parts. Some got help from mules. Excavation equipment, if the company used any, was huge, running on hand cranks, steam or gas.

Applying concepts used in basic concrete construction, builders poured the pools with expansion joints between wall sections and between the walls and the floor to accommodate natural earth movement. No sealants had been developed for these joints in underground and water applications, and builders didn’t seal pools with plaster yet, so these vessels leaked quite a bit.

The tiny pool construction industry of the 1930s, with its moneyed client base, largely escaped the ravages of the Depression and moved ahead to begin inventing ways to build pools cheaper, faster and better. Some builders even benefited from the glut of competent labor looking for work in these hard times.

Inland from the two coasts, pools remained the exclusive domain of public facilities, built mostly by general contractors. Wesley Bintz, for example, made a name for himself in the Midwest building “ovoid” pools for parks and municipalities. These $1 million, Olympic-sized aboveground projects were built like stadiums, surrounded by bleachers that sat above dressing rooms.

Paddock, in his efforts to improve the performance, appearance and cost effectiveness of pools, came up with the idea of finishing them with white plaster to serve as a waterproof barrier.

Also in the early-’30s, a man with the last name Nightingale, who worked for Cline, developed the first wet-niche light. It has kept the same basic form ever since.

Around 1934, Paddock developed a new method for pouring a pool shell: as a single, monolithic structure, eliminating the leak-prone expansion joints. One of the first pools built in this fashion was a 50-meter project at the Santa Barbara Biltmore Hotel in California. It required a monolithic base to overcome hydrostatic forces. In order to pour it all at once, crews worked non-stop for three days and two nights.

At about the same time, Ilsley began moving away from the more formal straight-wall pools and introduced the curvilinear pool wall and oval pool. He got the idea from German reinforced concrete domes built around the turn of the century. Some called these pools “inverted dome” pools; others called them “birdbaths.”

To construct these vessels, with walls that curved downward toward the center of the floor, crews installed rebar or a heavy wire mesh and then hand-packed, or dry-packed, concrete over it. This entailed dumping the concrete on the floor and building it up the walls.

Ovals remained popular through the ’40s because of the shape’s natural ability to evenly distribute forces, thereby resisting cracking.

Around 1938, Ilsley and Paddock began building freeform pools. Ilsley used his dry-pack method and boulders to form irregular contours for mountain lake-style pools, while Paddock offered curved ends and offsets to set apart his poured-concrete projects.

By the end of the decade, Ilsley had bought out Paddock’s business, which had become a nationwide company.