A well-maintained fiberglass pool or spa shell can offer decades of enjoyment to a homeowner. But even with regular checkups, shells can develop cracks and begin to leak.

“Leak repair is tricky business,” says Hank Lavery, owner of Millennium Pools in Springfield, Va. “It takes a lot of hands-on work. It really comes down to looking at the different components of the system, one by one, and pinpointing the spot where the problem is occurring.”

There are a few ways techs and other specialists can pinpoint leaks in fiberglass shells. Here, experts weigh in on temporary solutions to slow down or stop water loss through these cracks, as well as some of the more intensive renovations performed by fiberglass repair specialists.

TipThe process of elimination can be boiled down to 3 basic steps: pressure-test the plumbing, dye-test the pool water, and physically inspect the fiberglass. Walking through these steps will catch almost every leak.

Isolating the leak

When you head out on a service call involving a leak, it’s often impossible to guess where the problem lies. That’s why it’s critical to stick to a series of steps for narrowing the range of the problem. “Eliminate one part of the system after another, in a consistent order,” Lavery says. “As long as you follow the same procedure every time, you’ll eventually find the leak.”

Leaks on fiberglass installations fall into two general categories: cracks in the system’s fittings and pipes, and cracks in the fiberglass shell itself. As with other types of pools, most water loss can be traced to leakage somewhere on the system’s suction or return lines. To be a leak detection expert, however, you’ll need to begin by determining the exact rate at which water is being lost.

“Typically we start by advising the homeowner to perform a bucket test,” says Daniel Spatz, owner of Bullseye Leak Detection in Sacramento, Calif. “This lets us determine how much of the water loss is evaporation and how much is actually being lost out of the pool.”

The test is simple: A tech (or the customer) fills a bucket with water from the pool, places it on the steps, and marks the water level on the inside and outside of the bucket. After waiting 24 hours, the amount of water loss in the bucket is compared against that in the pool. If the pool’s water level has dropped more than the bucket’s, a basic subtraction reveals how many inches of water the pool is losing.

If you’ve determined that water is being lost, the next step is to investigate the plumbing and the equipment pad. Start by testing if the pump is having problems getting primed, since that can signal a suction-side leak, either underground or at the pump.

If the usual checks don’t seem to help isolate the issue, it could be time to call in a leak-detection specialist. These companies test for leakage with cutting-edge techniques, and they can track down even well-hidden cracks. Their series of steps, like the tech’s, begins by focusing on the plumbing and equipment pad.

TipSchedule your time generously for leak calls; there’s no way of knowing whether they’ll be resolved in a matter of hours, or drag on for several days.

“First of all, we disconnect all the equipment, and pressurize each part of the plumbing system by plugging off the pipe ends, then running water through the closed circuit,” says Hillel Salomon, owner of American Leak Detection in Berkeley, Calif. “If we detect a pressure loss on any of those systems, then we work with ultrasonic equipment to get a precise location on the leak.”

Ultrasonic detection equipment “listens” above the range of human hearing for distinct air and water vibration patterns that indicate a leak. By placing test plugs at strategic points in the plumbing, Hillel’s team is able to isolate the water cycle of each piece of equipment, and track any leak to its precise location — whether it’s in a pipe, in the deck or in the pool itself.

For cracks that are too large for water to produce ultrasonic vibrations through them, Hillel might try trace gas testing; this entails injecting a harmless gas — such as helium — into the plumbing, then “sniffing” for it with handheld molecular analyzers attuned to detect traces of the gas. “Sometimes these plumbing cracks are so big that you can’t build up any pressure, no matter what part of the system you isolate,” he says. “That’s when we use trace gas testing.”

Shells and penetrations

Other times, however, you may determine that the leak is in the pool shell itself, rather than in the plumbing or equipment pad. In this case, the next step is to pinpoint the spot in the shell where the water is slipping out. This can be trickier than checking the plumbing, because the parts to be inspected are underwater. But there are some likely places to start looking.

TipTo prevent staining and weakening of the shell, it helps to keep a fiberglass pool’s total alkalinity on the high end of the recommended range, between 150 and 200 ppm; and to keep the chlorine toward the low end, around 2 ppm.

“Wherever there are openings are in the shell, it’s common for fiberglass pools to leak,” Spatz says. “So, anywhere there’s a penetration, like skimmer throat; a return outlet; a light fitting; a main drain outlet — there’s potential for leakage.” In addition, it can be helpful to check around the base of the shell, where the walls begin to curve upward.

Spatz also emphasizes that cracks in the fiberglass itself often have different causes and cures than the more common cracks that form around penetrations. “Cracks in the shell are typically caused by roots, ground movement or uplift,” he says, “A lot of times, as fiberglass shells get older, they get cosmetic fatigue cracks; those are cracks that look ugly, but they don’t leak.”

To determine the source of an underwater leak, a good starting point is to inject some dye into the pool near suspect spots. The dye can be methyl red, which is normally used for pH testing and is contained in many test kits; or just some red food coloring.

The ideal procedure is to place a syringe underwater near the spot where you think the leak may be. Slowly inject dye into the water about half an inch away from the seal, and, if there’s a leak, it will be possible to see its location by watching the colored water move.

When repeated dye testing doesn’t seem to be isolating a leak, there’s one other technique that may help narrow down the crack’s location. “Turn off the pump, plug off the pipes, let the water level drop, and see where it stabilizes,” Spatz explains. “It’s going to stabilize below the level of the leak. So you can at least determine that the leak is at a certain level; you can narrow it down from there.”

If the damaged spot is accessible, then it may be possible to perform the repair yourself.

TipBecause draining a fiberglass pool voids the warranty on the shell, make sure the customer signs a liability release before you begin draining any water from the pool.

If this is the case, one choice is to replace the whole gasket, fitting, or light. An easier and cheaper option is to form a new seal between the gasket and the fiberglass with waterproof two-part epoxy. If that seal is still solid a few days later, it’s prudent to reinforce it with a second coat of epoxy, let that harden for a few more days, and perform a follow-up bucket test.

But if the epoxy never fully seals — or worse, if the crack keeps growing — Drew Anderson suggests one more technique to try. “I put a removable cap of epoxy on top of the crack,” says the president of Scuba Pool Repair in Campbell, Calif., “and I’ll leave a few tubes — about the diameter of a dime — in the epoxy to act as ports; water is only able to run through those tubes, instead of through the whole crack.” That way, even if water continues to leak, it only runs through tunnels in the epoxy, instead of eroding the edges of the crack.

These ports, Anderson explains, have another purpose besides reducing and directing water leakage. “I can then inject hydroactive polyurethane grout through the tube, behind the shell, where it’ll start to foam up,” he says. “So I can seal the leak from the negative side — from behind or beneath the shell. Once you’ve sealed the leak from underneath the shell, you can remove the epoxy, and you can perform surgery on the bottom of the pool without further loss of water.”

But if the leak can’t be fully sealed, even by sealing up the shell from the negative side, the fiberglass itself may be in need of refurbishment. This is where most pool techs call in the specialists.

Major mending

For shells with sizable cracks, or ones that continue to grow, more drastic (and expensive) solutions become necessary. Most of these fixes involve draining the pool, at least to some extent, and patching the crack with a combination of adhesive materials and sheet fiberglass.

Daniel M. Tucker is one of the specialists who gets called in for this sort of work. The owner of Fiberglass Pool Resurfacing in Martinez, Calif., starts by draining the pool. His team then fills up the crack with a high-pressure epoxy injection, and attaches one or more layers of sheet fiberglass — depending on the severity of the damage — over the crack, sealing them to the shell’s surface with polyester putty.

Experts like Tucker also get called when bulges appear around fiberglass shells, and they begin to crack. These bulges are the result of a pressure imbalance: if the sand backfill remains wet (and thus, expanded) but someone has drained the water out of the pool at some point, the sides of the shell often will begin to bulge inward.

TipBe aware — and be sure the customer is aware — that all fiberglass shell repairs are potentially temporary. Whatever conditions caused the shell to crack initially may still need to be addressed.

“We’ve tackled some of those where we’ve actually had to cut the bulges out,” Tucker says. “And when you do that, the sand starts pouring into the pool through the hole, like in an hourglass. So we end up having to clean all that out of the bottom of the pool.”

With these and other large openings in fiberglass shells, Tucker uses a multi-layer strategy. After draining the pool, his team inserts a piece of weather-treated plywood into the backfill behind the opening; they then fill the gap with self-expanding A-B polyurethane foam. Finally, they shoot a new coat of fiberglass over the entire shell, and refill the pool.

But even a repair like this can produce somewhat inconsistent results in the long term, Tucker says. “It’s risky at best, because you don’t know how strong the shell is. Some manufacturers put a lot of sturdy material in their shell; some don’t. But for all manufacturers, as far as I know, draining the water out of the pool voids the warranty on the shell. And you can’t do repairs like these without draining the pool.”

Even if your main focus is basic leak detection, though, it helps to know what to recommend. Keeping your fiberglass repair instincts sharp will ensure that when there’s a pipe leak to be detected, a crack to be isolated, or a specialty crew to be called in, you’ll know which option works best for the job.

“We try to keep specific crews working on leaks,” Lavery says. “If I go out and work on leak jobs for five or six days in a row, by the seventh or eighth day, I’m so much better at it. The more you do it, the more of a feel you get for it: sounding, listening, looking — repetition makes you so much better at all of it.”