There’s nothing glamorous about waterproofing. It doesn’t dazzle in the portfolio and it likely doesn’t enter into most customers’ minds.

That’s why it’s an easy step to skip, as Alan Smith sees during competitive bidding. He recently lost a high-end job in Malibu, and he suspects the waterproofing cost was a culprit. His company needed $3,500 for that part of the project, but the builder who eventually got the contract didn’t mention waterproofing in the bid.

Unfortunately, Smith suspects, the customer will pay. “It’s not if it’s going to be a problem — it’s when,” says the owner of Alan Smith Pool Plastering in City of Orange, Calif.

The omission or half-hearted execution of waterproofing becomes visible soon enough in the form of efflorescence or delamination. Vanishing edges are showing the most problems, with tiles and stone falling off.

And it’s not just a matter of brushing on a sealant. “There are so many things you can do wrong during that process,” says Gene Brown, president of Valley Pool & Spa in Kelowna, British Columbia, Canada. “It’s a bit of an art form all in itself.”

Here professionals discuss this process and its many considerations.

Vanishing-edge issue

Though waterproofing is needed in different kinds of situations, vanishing edges have been causing the most problems of late.

Of course, any surface that will be veneered with tile or stone should be waterproofed, but some professionals have struggled with vanishing edges resulting in efflorescence and fallen tile or stone on the back side of the wall.

If a vanishing edge isn’t properly sealed, the falling water can cause efflorescence to form. Perhaps less known is the fact that water from the main pool can seep through the weir wall and form efflorescence behind the tiles or stone on the back of the wall. As the calcium builds up, it eventually can cause the finishing material to pop off.

And it’s not just water. “It’s also vapor,” says Greg Andrews, owner of Andrews Tile in Agoura Hills, Calif. “If you get water or moisture entering from the pool side and then the other side ... can heat up to 120 or 150 degrees, it can actually pull vapor through.”

Because of this, vanishing-edge walls should be waterproofed on both sides. Applying a system to the main-pool side keeps water from seeping through. This is called the positive side because it’s the source of hydrostatic pressure on the wall. Sealing the back of the wall, or the negative side, forms a barrier in case water does seep through, and also helps protect against the water falling over the weir.

Many professionals will waterproof the entire wall inside the pool — not just the section with spilling water. They often continue adding the agent down the back of the wall, into the catch basin and even over the lip of the catch basin. Different compounds may be needed to address positive pressure and negative pressure.

Spa dams should be treated similarly. Many professionals will waterproof the entire spa interior, as well as the face of the raised wall.

Because the weirs and backsides of vanishing-edge walls are always veneered in tile or stone (since plaster and pebble surfaces need constant immersion), Dave Peterson, president of San Diego-based Watershape Consulting suggests following the instructions provided by the Tile Council of North America to waterproof the weir and back wall.


Regardless of the situation, it’s crucial to use the right system and apply it correctly. Contractors should begin by making sure that the waterproofing agents they’re choosing are appropriate for the project at hand.

Read manufacturer’s specifications to establish three things — whether it’s appropriate for water vessels, whether it protects against positive pressure, negative pressure or both, and whether it can be mixed with other systems that may be needed. Some companies will only warranty their products when combined with others in their line. Additionally, makers of topical membranes may not allow these products to be utilized in combination with waterproofing admixtures.

Don’t assume that because a system has been proven in other types of construction, such as bridges or vaults, that it’s appropriate for pools and spas.

“We have a different protocol for placing [concrete] than other industries,” says Ken Milbery, divisional product specialist for PoolCorp’s Pacific Division. “We apply ours with force and we very seldom see the situation where we’re basically adhering to a [formed and poured] shell. Shotcrete and gunite ... it’s a more porous placement than a compacted, integrated mix design from a ready-mix plant.”

“Some waterproofing materials are made to go under maybe an elastomeric coating, not under something cementitious going over the top of them,” Smith says. “You have waterproofing materials that are designed to go under deck coatings on balconies, and they don’t have pool water with acid and chlorine sitting on them constantly.”

Often, contractors find themselves using at least two types of waterproofing agents — one for around the fittings and another for the flat surfaces. The material used around the fittings must be thicker to fill the gaps, while the waterproofing agent on the rest of the pool should be applied in a thin layer.

Good foundation

When applying the waterproofing system, start by inspecting the concrete to make sure it’s in good condition.

If there are divots and holes, it may be necessary to add a float. Some waterproofing products can’t fill holes in concrete, so these materials need to be applied on the smoothest possible surface.

“Especially like with the shotcrete we use, the aggregate’s fairly large so you tend to see a lot of imperfections in the surface,” Peterson says.

Professionals also should look for hollow spots. This is particularly important on vanishing-edge walls and others that are self-supporting, because of how they’re constructed. “Most times ... when they shoot the pool, they’re generally shooting up against the earth,” Andrews says. “But with infinity-edge walls, they’re shooting up against a form, and there can be some vibration of the form and/or the steel that’s in the wall.

When that happens, it can create voids, and if water gets to those voids, then that can spell disaster.”

He not only performs a visual inspection, but taps around the wall to check for hollow sounds. If he comes across one, he will chip the concrete to expose the void and then fill it.

Contractors also should always ensure that the membrane will bond properly with the next layer being applied, whether another coat of waterproofing, a thinset or plaster-like material.

“The issue you’ll run into is the membrane will stick to the concrete no problem. But the problem is getting the pebble or one of those finishes sticking to the membrane,” Brown says. “Once they’re dry, they’re now really waterproof, so the next layer has a hard time biting into that — because they’re doing what they’re supposed to do.”

Manufacturers may recommend a particular bond coat to be placed over their product. But if the waterproofing agent is cementitious, applicators should somehow rough up the surface, whether it be by running a notched trowel over the top to create a grooved pattern or texturing it with a brush or roller.

“If you do not follow those instructions you can end up with a surface that’s way too smooth and you’re not able to bond to,” says Jay Eaton, general manager of Phoenix-based Cal Plastering Co. “Then it’s like trying to put pebble on glass. It won’t bond.”

The details

Once you’ve determined the product is appropriate, it’s important to follow the instructions to the letter. There may be more steps required than you realize.

“There’s actually a lot to a membrane, and if you really go through how it’s supposed to be done, there are a lot of steps that most people just run over,” Brown says.

For instance, some products must be applied within certain temperature ranges. Some are more sensitive than others. Because of this, Brown often tents his projects as he’s waterproofing them. “Part of this is for sun and to keep the adhesives from flashing to the membranes and getting some weird drying aspects,” he says. “It doesn’t matter if it rains or there’s sun, because all of it’s bad. You just want to keep a nice, constant temperature. If you seal it up and sort of treat it hermetically where it’s a controlled environment, then you’ll generally have success.”

In one recent Phoenix-area project, plasterer Eaton not only had to tent the pool, but he and his crews also had to use coolers. “We couldn’t use the [waterproofing] product because it was just too hot,” he says. “I believe we were keeping the structures at 78 to 82 degrees.”

While not always necessary, tenting also helps with another important aspect of waterproofing — maintaining a clean environment.

Manufacturer instructions may even specify a rate at which the pool should be filled, and how much time should pass before it is heated for the first time.

Other waterproofing systems don’t work well when placed around hard corners, which may cause the layer to crack. If this is the case, instructions will explain how to round out the corners to make the surface more effective for the compound.

If the membrane is being applied to a pool built over a house or other structure, it’s best if plasterers don’t puncture it by walking with spikes. To avoid this, Smith’s crews will place a thin layer of cement or other substance on it so crews can walk on the floor without puncturing the membrane.