Finishes and practices for making pool structures as watertight as possible
By Michelle L. Cramer
Though a concrete pool structure will never be 100 percent watertight, achieving an adequately sealed pool requires reliable materials and techniques. Steve Goodale, owner of SwimmingPoolSteve.com and a swimming pool specialist in Ontario, Canada, points out that because concrete is a porous construction material, “at most you are attempting to make a highly water-resistant structure.” Concrete will absorb and leach water through to the substrate, he says, which will wick into the ground surrounding the pool. “This is the reality of how concrete pools work,” he says.
With time and aging, concrete pools become more porous and water wicks through to the substrate at a dramatically increased rate, slowly eroding the concrete, Goodale says. “What many novice concrete pool builders might not appreciate, and certainly the average pool owner does not appreciate, is that making a concrete pool waterproof is a losing battle right out of the gate,” Goodale says.
Mistakes during the construction process can mean this small, expected leaching of water may become a full-blown leak, however. Goodale says pool builders should minimize leak concerns with a concrete structure by, to begin with, pouring or shot the concrete shell in one continuous pour, with no cold joints below the waterline.
“When applied properly, shotcrete does not create a cold joint, even when new concrete is applied to existing concrete,” Goodale says. “This is due to the sandblasting effect from the force used to apply the concrete. However, some pools are not built in one pour, such as form and pour pools with the floor built first and then the walls later. While these pools can be as water resistant as shot pools, they are more likely to develop leaking issues due to the cold joint below the waterline.”
To minimize leaking, Goodale recommends that:
- All pipe penetrations through the wall of the shell have water-stop devices installed to prevent water from tracing along the pipe and escaping the structure.
- All intrusions in the shell — such as main drains, lights and skimmers — be formed out to allow for concrete to substantially encase the device on all sides.
- The pool be built on virgin — not previously excavated — earth or on a compacted medium of only one material type, so that it settles evenly in the ground.
- A reinforced steel grid be installed to meet or exceed engineering requirements for every structure.
- Every spot a pipe penetrates the pool wall be turned downwards with a 90 degree fitting. Otherwise, if the pipe sinks even by a small amount in the overdig, the connection point will crack. (Goodale says this is one of the most common — and preventable — causes of leaks.)
Arthur Mintie, senior director of technical services at LATICRETE International, Inc., in Bethany, Connecticut — which manufactures ceramic tile and stone installation materials and accessories — agrees that the penetrations through the water vessel shell are usually the weak points. “Using a stable, flexible sealant that is designed for use in submerged applications is a must to treat penetrations that interface and tie in with the waterproofing membrane,” Mintie says. “In addition, transition areas are also potential weak points — gutters, copings, expansion joints — so proper detailing of these critical areas is also important to maintain waterproofing integrity.”
Even vinyl-liner and fiberglass pools are not going to be completely waterproof, according to Goodale. “When built properly, a vinyl liner is 100 percent leak proof, however, once installed into the pool, a number of potential leak locations are introduced,” Goodale says. “Vinyl and fiberglass pools leak around the gasket and flange systems for the skimmers, main drains and returns.
Even though the interior surface itself is waterproof, the structure as a whole is not.”
Let the Process Seep In
Mintie says he believes there is a solution for any condition a pool builder may encounter; the key is being thorough. “Whichever waterproofing type product is selected, it has to form a continuous waterproof pan effect with no interruptions to ensure complete waterproofing,” Mintie says.
This method is what Andy Sancomb, sales manager at National Pool Group (NPG) in Glenelg, Maryland, refers to as the “system approach”— stopping the migration of water through the pool wall and providing a flexible cement membrane that will expand and contract with the movement of the pool shell.
NPG’s process for a new pool shell with a raised wall, negative edge, glass tile and/or spill over spa is as follows:
- Apply Aqua Blok XL as soon as you can walk on the shell, misting the shell with the first coat applied horizontally.
- Once the first coat is nearly or completely dry, mist the wall and then apply a second coat vertically.
- After 24 hours, thoroughly pressure wash the areas where ABXL was applied, without chemicals.
- Membrane C would be applied next: Mix the 2 gallons of component liquid with a 43-pound bag of the Membrane C in a five-gallon bucket. Saturate the wall first and then remove any standing water, then roll on the Membrane C with a 1/14 nap roller that is 33mm thick.
- There should be no puddles, dripping or sagging. The Membrane C goes on blue and is gray when dry. Apply a second coat when there is no blue, without wetting the walls.
- Plaster applications require 12 hours to dry and then the application of BC Pro bond coating.
Mintie advises that using a waterproofing membrane in just a partial manner — such as banding the rim of the pool or waterline — can allow water to work its way under the membrane, increasing its chances of coming loose.
“To avoid this, waterproofing should be used throughout the entire vessel in order to contain the water,” Mintie says. “Instead of a concrete shell, think of a cup that is holding water. If it is not completely waterproofed, there is no sense in using it, since water can seep around the unsealed areas and render it useless.”
The Fancy Stuff
Goodale notes that even fully tiled pools — the “Cadillac of high-quality interior pool finishes,” he says — will still leach water through grout joints and installation imperfections. Mintie says the first step is to identify the appropriate tile application standards from the Tile Council of North American Handbook that apply to the pool construction, and then adhering as closely as possible to those standards (after sealing the membrane).
While LATICRETE is not involved in specifying finishes, the team has observed which finish types perform better over time. “Typically, porcelain bodied mosaics and other porcelain tile types that are suitable for submerged applications have a great track record of success,” Mintie says. “In addition, glass tile that conforms to ANSI A137.2 requirements works really well too.” Mintie advises, however, that the mounting of mosaics and the bonding area of the tile are critical to long-term success.
As such, builders should steer clear of tiles (and stones) not designed for submerged applications. These finishes may have a high porosity, Mintie says, and could absorb water, failing due to moisture expansion. Additionally, it’s difficult to waterproof a pool with multiple finishes, such as a plaster pool with tiling at the waterline and steps. “When pool plaster is utilized in conjunction with tiling, the waterproofing requirements should default to those of the pool plaster manufacturer,” Mintie says.
A Consistent Approach
While Ken Milbery, director of technical services at Lunada Bay Tile in Harbor City, California, has been working with and prefers all glass-tile pools (for the aesthetic appeal), he believes that most of the pool finishes available today are quality products, if installed properly.
“The real issue is we, as an industry, need to get everyone on the same page and talking about methods and materials,” Milbery says. “All of us must come together to create standards and recommendations — designers, builders, manufacturers of materials and pool finishes, and the service industry. It’s critical for all of us to be on the same page.”
Sancomb says he believes builders should stop relying upon traditional methods and take the time to learn what waterproofing options are available. “Pool builders need to stop saying ‘We have been doing it this way for years,’ ” Sancomb says, mentioning that education programs offered through National Plasterers Council, Poolcorp, APSP and others are readily available. “Use these to see how other pool professionals are fixing problems that have plagued us all for years,” Sancomb says.