If you ask someone to create their dream pool, it seems, more than ever, it would include a window or see-through wall.
That was the case with last year’s Million Dollar Pool Design Challenge, where several of the submissions included viewing windows or see-through walls, many with vanishing edges.
“They’re the next sexiest thing, and everybody wants to be part of that,” says Rick Chafey, co-owner of Red Rock Pools & Spas in Mesa, Ariz.
But simply adding this component tips a project into the category of most technically challenging. Joining acrylic or glass to concrete creates another opportunity to leak, which would be catastrophic, especially if that window is connected to the home. But other concerns may not reside top of mind. Here, designers and engineers highlight the keys to making these projects hold up structurally and aesthetically.
The material
For the most part, glass has gone by the wayside in favor of acrylic, for several reasons. It’s more workable — it can be made in larger, thicker panels, and it remains clear regardless of thickness, where glass begins to take on a green tinge. Perhaps most importantly, acrylic will provide hints before it fails, where glass will just blow.
In the case of acrylic, thickness will be determined based significantly on the need to prevent deflection, says David Peterson, president/CEO of San Diego-based Watershape Consulting. While deflection generally won’t cause the panel to fail, it will create microscopic cracks that compromise clarity. And at a certain point, deflection will cause the material to bulge, which looks unsafe even when it’s not.
Acrylic panels are made in a furnace, so they can only be so long. Peterson has found lengths of more than 24 feet are difficult to source. For more length, panels may be fused together on site so they look like one long panel. Or they can be joined with a mullion, a thin vertical separator between the panels, in this case made of stainless steel.
When looking to create a two-sided acrylic wall, sometimes two panels can be fused together to create a seamless look. But some manufacturers limit when they will fuse corners. One, for instance, won’t do it with panels thicker than 3½ inches.
Fusing corners can create undue stress on that spot, Peterson says. “Imagine you have an L-shaped window and, in the heat, the two [panels] are pushing toward each other at perpendicular angles ... it’s really stressing out that corner. ”
In many cases, he’ll recommend using mullions instead of fusing. That’s not as important when temperatures remain constant and/or the panel is always immersed in water, he says.
In the field
Most pool builders do not install windows or panels. Instead, they rely on specialty installers or manufacturers who perform that service. Each of these specialists have their own method.
Installation varies between windows that are supported on four sides, versus those acrylic walls that may serve as a vanishing edge. With the latter application, installers must work to prevent rotation of the wall, since they’re not supported on top. To do this, Peterson says, the walls must be placed in a deeper slot in the floor — at least three times the thickness of the acrylic — then packed with a non-shrink grout. “So at the end of the day, it’s like the panel and the concrete are one and the same,” he explains.
On the other hand, windows that are supported on all four sides by the shell should go into the concrete by at least the thickness of the panel. If you have a 4-inch-thick panel, then it should have at least 4 inches of bearing all around, meaning it goes into the concrete by that much.
When forming the area around the window, the opening should be large enough to provide at least another inch of clearance to make room for the blocks, backer rods and sealant that the installers will use to secure the panel and set it in place. Be sure to consult with them when determining this.
The pool shell will be thicker than the acrylic or glass panel. Generally, designers like to place the window so it’s flush with the pool interior, so there will be a recessed area in the wall. This is called the rebate.
The rebate isn’t just the byproduct of needing a thicker wall or floor than the acrylic or glass — it plays a key role in supporting the panel. “You need the concrete structure to kind of reach around the backside of the window and keep the window from popping through,” Peterson says.
Even if the panel is only 4 inches thick, you’ll probably need a wall at least 12 inches thick around it. “That doesn’t mean all the walls need to be 12 inches thick,” Peterson says. “But at least around the window they probably need to be 12 inches thick so you could have 8 inches of concrete on the backside of the window to hold it in.”
Design considerations
When planning a pool with acrylic panels, designers must consider several moving parts to ensure they last and look good.
• Consult the engineers: Whether incorporating an end panel or window, the pool should be engineered.
Preventing leaks entails not only using the correct caulks, grouts and waterproofing agents, it also requires a structure that’s engineered to support the panel, says Rob Holmer, a principal engineer working from the Sacramento, Calif. office of national engineering firm Terracon.
“The water is going to push against the window,” he explains. “The concrete sill structure and the surrounding swimming pool shell need to be designed and constructed to transfer the loads on the window itself out to the sill. So the concrete framing around the window will have higher loads than would be subjected to a standard pool.”
So engineers will generally specify more steel reinforcement than normal, as well as higher-strength concrete mixes.
Holmer generally recommends that the area around the panel be made of poured-in-place concrete, rather than shotcrete or gunite. The forms will leave a cleaner, flatter, smoother surface, making it easier to keep the glass straight and to apply the waterproofing membrane.
If the rest of the pool will be made of shotcrete or gunite, then a cold joint is needed to properly bond the cast-in-place window frame area and the shot product.
Engineers also will help determine what waterproofing membrane should be used on the wall or walls around the window or panel. (On this front, you also must find out what waterproofing system the installer will use directly around the panel and ensure that the two are compatible.)
• Finish considerations: To keep things as clean as possible, Peterson places a tile border around the panel extending 3 to 6 inches out. This way, if plaster, pebble or other troweled material is used on the interior, the applicators and their equipment will stay healthily away from the window.
“If you do it right at the edge of the window, then as you’re buffing and cleaning up the plaster, you’re probably going to scratch the window,” he says.
• Expansion/contraction: Because it is a relatively soft material, acrylic expands and contracts more than concrete. So the see-through panel will swell more when it’s hot and shrink more when it’s cold. “Maybe the pool moves ¹⁄₆₄ inch,” Chafey says. “But the panel might move ⅛ inch or more.”
For this reason, flexible grouts and waterproofing agents are generally used, though each manufacturer and specialty installer makes their own recommendations.
Because the amount of movement can increase with the panel’s size, Peterson likes to limit the length of single or fused panels. When they exceed a certain size, he often connects smaller panels with mullions. This allows each piece to move separately.
For acrylic end panels used to make a vanishing edge, this is particularly important. Not only will the panel expand and contract from side to side, but it will grow taller in the heat and shrink shorter in the cold. Consider this when using an acrylic panel as a vanishing-edge. Try to avoid installing during temperature extremes, and engineer the hydraulic system accordingly: When the wall grows taller, the water still needs to spill over it. So design the hydraulic system for more water in transit than you otherwise would. Additionally, prepare the service technician, operator or homeowner to adjust the flow as needed during temperature extremes. This especially becomes important with two-sided vanishing edges, or when a vanishing edge meets up with an overflow slot, because you need to ensure that water spills on all sides.
• Establishing expectations: It’s true that acrylic panels can singlehandedly add another layer of stunning. But that happens only from certain vantage points.
As with vanishing edges, the illusion will not hold from every angle and distance. While an acrylic end wall can make a pool look like a block of ice from some spots, reflection and refraction will cause it to look like a solid wall from others.
Chafey designed and built a rooftop pool with glass panels on the outside edge, where it could be viewed from the yard below. From ground level, one can see into the pool and you get that block-of-ice effect.
“When you’re on the deck side and you think you’re going to look out and see through the water and through the panel and down to the ground, it doesn’t even happen,” he says.
That effect doesn’t occur until you’re standing on the coping directly opposite the panel, he says, but not from farther away. “If you have an acrylic-panel negative edge and you’re 30 or 40 feet away looking at that edge, as far as the viewer’s eye, it might as well be concrete,” Chafey says.
This isn’t conveyed with 3-D drawing software yet, so renderings and videos make the acrylic ethereal from every angle. So designers should warn homeowners.
• Keeping it clean: On the other hand, a key point of attraction for acrylic is its crystal clarity, especially from close up. That means that, from spots, you can see everything happening in the pool. Plus, thicker acrylic will act like a magnifying glass. This can pose problems if certain measures aren’t taken. “If you’re going to be looking at the pool through the panel, you have to make sure the inside of the pool looks perfect,” Chafey says.
He remembers seeing spas with acrylic panels at a resort. “In the mornings, they all look decent,” he says. “If there’s a big pool party going on, it is the grossest-looking water you have ever seen in your life!”
To combat this, designers should boost filtration and use cartridge or diatomaceous earth to sift out smaller particulate, especially on commercial installations, because of the higher usage.
But that’s an easy solution. More problematic are workmanship errors that can show through the acrylic. Flaws and irregularities in step forming or interior finish become magnified. Even worse, any sloppiness in the joinery between the panel and pool shell also become obvious. That bead of caulking or layer of setting material isn’t going to be very attractive.
To help conceal the latter issue, panels should be painted where it will make contact with concrete. If it will be set 4 inches in the shell, then a 4-inch edge should be painted. If the panel will sit flush with one side of the floor or wall, then it should not be painted on the flush side, as it will be visible. This means builders must know exactly how much of the acrylic’s edge will make contact with the concrete, so the right amount is painted. If too little is painted, then caulk and the like will show in the unpainted area.
If he can, Chafey will avoid placing a panel where the pool interior can be viewed from the outside close by. He tries to situate the panel so people can see out from inside the pool, and so they can look in the pool from a distance.
