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Op Editorials

Best Practices to Prevent Water Intrusion



Grant Smith explains why tiles fall off and why water intrusion happens, also how to prevent it.

There always seem to be a discussion on here about proper coverage behind tile and why the TCNA specs at least 95%. Water intrusion is one the key reasons. Over time water will work it’s way into the hollow spots or grooves and slowly work on emulsifying the remaining thin set that is behind the tile which brings out efflorescence and will eventually make the tile fail and come off.

When you apply the dotting method or leave grooves behind the tile from the trowel it allows water behind the tile. As you can see in some of the pictures presented here the large format tile fell off one day because of a combination of dotting and leaving grooves.

In the picture of the blue translucent glass tile you can see the grooves behind the tile and there is now mold growing in the grooves.

This pool had many other issues which I will post later about. If you back butter the tile and then knock down the grooves that the tile trowel makes this will ensure you have the proper coverage and it doesn’t allow water in those channels. This is especially important in translucent glass.

When you install the tile thin set should be squeezing out of the joints and you will spend time cleaning the joints out. It is typical that I will use twice as much thin set on a project than what the coverage rate says on the bag.

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In Memoriam: Grant Smith - featured Op-Editorialist for Pool Magazine and President of Aqua-Link Pools and Spas in Carlsbad, Calif. A former SWD Master, Watershape University faculty member, mentor and instructor; Smith was widely recognized as an expert and thought leader in the swimming pool industry.

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Swimming Pool Expert Witness - Paolo Benedetti

Utilizing Drainage Mats In Pool Construction



Pool Contractor Using Drainage Mat During Pool Construction

Retaining walls, raised pool bond beams and pools with adjacent upslopes all require drainage behind them. But it is impossible to install drainage rock up the walls of a shotcrete pool, without extensive over-excavation, forming and backfilling.

Instead of ignoring these conditions, wise contractors utilize drainage mats installed upon the earth, prior to the placement of the shotcrete. This allows the subterranean water to drain vertically into the drain rock under the pool, where it can be collected and discharged (drained to daylight or via a sump pump).

For high-end projects or all tile vessels, this is critical in reducing negative side water infiltration from the soils. Water passes through the geofabric and into the air gap created by the dimples in the plastic sheet. The drainage mats are available with dimples of various sizes to match the anticipated water flow.

Drainage mats can also be used horizontally between coffers and vessels to assist in the lateral discharge of water. The drainage mats can be nailed to the soil prior to steel placement or utilized in place of steel-tex.

Photo Credits: Carlisle Coatings & Waterproofing Systems

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Swimming Pool Expert Witness - Paolo Benedetti

Indoor Pools & Water Vapor, What You Need To Know



Indoor Pools & Water Vapor, What You Need To Know

Indoor pools are very unique. The water vapor escaping from the pool is trapped in the building envelope. These vapors are potentially corrosive, as they contain chlorine, chloramines, or ozone. The water can have destructive consequences and pose serious health issues if the building is constructed incorrectly.

Dehumidification of indoor pools is absolutely essential in order to avoid costly damage and repair work.
Dehumidification of indoor pools is absolutely essential in order to avoid costly damage and repair work.

Dehumidification for Indoor Pools

There is no such thing as an oversized dehumidification system. But the lack of a dehumidifier (or an undersized one) allows the water vapor to accumulate and penetrate the building envelope. Water vapor inside the walls can cause corrosion of the structural beams, braces, and brackets, corrosion of the wiring and electrical components, foster mold and algae growth, rusting of HVAC ducts, or promote dry rot of wooden elements. Excess water vapor in the building can lead to a series of air-borne health maladies or bacterial infections.

Indoor pool mold from excess water vapor.
Indoor pool mold from excess water vapor.

Been There, Done That

Cheap clients who do not want to pay for the installation or operation of a dehumidification system, think that they can reinvent the wheel with exhaust fans, sliding doors, skylights, ceiling fans, or other schemes. Trust us, they have been tried countless times without success.

Proper Building Envelope for Indoor Pools

It is important to install a vapor barrier and use moisture-resistant construction materials to prevent the migration of moisture into the walls and ceiling. Electrical outlets, fixtures, and penetrations must be sealed against vapor intrusion.

Without Vapor Barrier vs With Vapor Barrier - Indoor Pools
Indoor Pools – Without Vapor Barrier VS With Vapor Barrier – Photo Credit: Aquatic Mechanical Design

Air Pressure in Indoor Pools

The air pressure within the swimming pool enclosure must be less than the adjacent spaces. Maintaining a high pressure in the adjacent spaces ensures that the water vapor does not migrate.

Operational Cost

Operating a dehumidification and air handling system to control the air pressures, temperatures and humidity are expensive to operate. Failure to operate these systems properly will result in vapor migration and degradation of the building. Maintaining the proper temperatures is also important in controlling the creation of water vapor (evaporation).

Automatic Pool Cover

Using a pool cover does not eliminate the need for a dehumidification system. It will help reduce the vapors, but it will not eliminate them. The installation of a cover allows for the reduction in the size of the dehumidification system, as the loads are reduced.

Qualified Indoor Air Quality Expert

We do not profess to be experts in this field. Though we have built a number of indoor pools, we rely upon specialists in this field. Most mechanical engineers or dehumidifier manufacturers do not possess the skills to properly design the HVAC/Dehumidification system, vapor barriers, building envelope, ducting sizes, or air handling register/return locations.

Non-Corrosive Air Ducts

Properly constructed indoor pool air handling systems utilize non-corrosive plastic ducting, registers, and returns. Galvanized sheet metal ducting quickly begins to corrode in an indoor pool environment. Indoor pools can be a source for year-round enjoyment of a pool. But they require a properly designed and built enclosure, in order to protect the rest of the building and occupants’ health.

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Op Editorials

Flawed By Design – Skimmer Lids, Drain Covers, & Fittings



Flawed By Design - Paolo Benedetti - Swimming Pool Expert Witness

With the ready availability of colored pool fittings, there is no excuse for using mismatched skimmers, drain covers, wall fittings or plastic lids. Concealing these “architectural uglies” is easy – things most pools require, but no one wants to see.

SKIMMER LIDS (and deck lids)

There is absolutely no excuse for using plastic skimmer lids. Besides being a visual distraction, they only last a few short years. For concrete, stone or pavers there are the round or square pourable lids. Their non-metallic design eliminates the requirement for bonding, electrical safety that metallic lid trays simply disregard and ignore. They are even available for most popular laminar fountains. If the deck is overlaid with a thick & dense stone, simply manufacture a lid out of stone.


Covering the deck with multiple plastic or brass drains, or worse yet linear plastic drain channels creates visual clutter. Again, there are pourable deck drain covers – available in a combo 3 & 4 inch size, 6-inch size and linear slot drains.


Why distract from the beauty of the pool with white plastic drain covers that distract from the exotic finish, pebbles or mosaic tiles? There are even drain covers available that accept troweled or tile finishes – floor returns, drain covers, channel drains and even for in-floor cleaning heads.

Pool Drain


As with floor drains, why distract from the surface finishes with fittings that do not match or protrude from the wall? There are a myriad of flush mounted and colored fittings to match almost any color finish. For those finishes that do not come close to matching the standard colors, there are clear fittings that blend with any finish color. With a little bit of effort these items can be concealed with minimal expense.

Resources:…/precast-trench-drain/vector-drain (We use these and tile over the rims, leaving just an ungrouted joint – super clean look)

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