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Cementitious Water Damping Products Help Prevent Failures

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Grant Smith explaining water dampening - concrete cracks

Let’s talk about tile and why it’s important to install a flexible cementitious water dampening product behind it. Concrete cracks including shotcrete whether dry or wet. Dry is less likely to crack because of the low water to cement ratio but it will at some point crack. Most cracks are due to shrinkage because as concrete cures it expels moisture and changes volume and gets smaller and something has to give. Shrinkage cracks in pools are not an issue.

The American Shotcrete Association addresses shrinkage cracks in pools and the proper way to fix them. There are damp proofing manufacturers that have specific protocols to fix them. When it comes to tile especially glass tile there is a reason why manufacturers require a cementitious flexible membrane.

After waiting the 28 day cure time before applying tile the concrete is still curing and changing volume. In addition to allowing the tile to flex a membrane allows flexibility so if you incur a crack it will not affect the tile. Take for example the pool in the pictures attached to this post. I was called out to look at water dampening this pool because the owner felt the shrinkage cracks in her negative edge wall was a signal the pool was failing and needed extra help.

This was the least of her problems. Besides the abhorrent shotcrete job and hydraulics the tile was popping off on the edge wall right where the shrinkage cracks were due to the tile installer not installing a membrane to allow the tile to flex as the shell was losing volume. Concrete can take decades to fully cure which is even more reason to install products that will make your tile installation counteract the curing process. As the pool sat and cured with the tile installed and shrinkage cracks appeared it popped off the tile and led to a failure of the tile.

It’s important to follow TCNA protocols and those from the manufacturer.

Grant Smith

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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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Op Editorials

Hair Entanglement in Pools, Are Current Standards Adequate?

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Hair Entanglement in Pools, Are Current Standards Adequate?

When discussing hair entanglement in the pool and how to prevent these types of incidents from occurring, we have to look at a few things. The first is line velocity. If it is low enough, hair won’t be ingested by the pipe and tangled under the drain lid. Suction entrapment wouldn’t occur either, even if a grate were missing.

Video captured a teen girl nearly drowning after getting her hair caught in the pool.

The second issue pertains to the current codes and standards. Some states have state building codes that dictate maximum line velocities for energy efficiency. California and Florida both mandate line velocities of 6 FPS suction and 8 FPS returns for energy efficiency. 

Current Standards

Residential In-ground Pools NSPI-5/2003 (9.2) the line velocities were limited to 8 FPS suction and 10 FPS returns. (9.2.1) the limit through the drain cover was limited to 1.5 FPS.

Residential In-ground Pools NSPI-5/2013 (9.2) the line velocities were limited to 8 FPS suction and 8 FPS returns. (9.2.1) the limit through the drain cover was deferred to the APSP-7 standard.

Suction Entrapment Avoidance APSP-7 (2013) Piping line velocity is not specified, though the flow rate through the drain cover is limited to 1.5 FPS.

APSP-15 Energy Efficiency Code (2011) 6 FPS suction and 8 FPS return

ISPSC 2015 (311.3) limits the line velocities in the return piping to 8 FPS.  (310) It defers to the specifications in APSP-7 (there is no longer a suction line velocity in the standard).

Suction Outlet Fitting Assemblies APSP-16/2017 (3.9.2) piping line velocities were eliminated, though 1.5 FPS remained as the line velocity through the RDP/SOFA.

RE: Hair Entanglement In The Pool - Decreased distance between the suction pipe and the underside of the drain cover increases the flow through the drain cover.
Decreased distance between the suction pipe and the underside of the drain cover increases the flow through the drain cover.

The safety standards are not addressing energy efficiency. Most experts agree that the optimum efficiencies are achieved at 6 FPS suction and 8 FPS return line velocities. The majority of hydraulic engineers are designing at 4.5 FPS suction and 6 FPS return line velocities. This allows for a margin of error and minor deviations that may occur during construction, while still staying below the maximums. Most codes for public pools recognize the need for low line velocities and therefore limit the velocities at the pipe connected to the main drain to 1.5 – 3 FPS.

The safety standards assume two things occur. The first assumption is that the drain sump size is compliant with the SOFA requirements and the manufacturer’s specifications.  Field-built sumps (divots carved out of the shotcrete) are oftentimes too shallow. Few builders thicken the shotcrete around the suction pipes to allow for a proper depth sump.

The decreased distance between the suction pipe and the underside of the drain cover increases the flow through the drain cover. This increases the danger of hair entanglement, as the design standards and flow rate through the cover have been exceeded. Therefore the sumps are of insufficient size and volume to slow the velocity of the water.

Swimming Pool Expert Witness

Photo Credit: Getty Images

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Swimming Pool Expert Witness - Paolo Benedetti

Utilizing Drainage Mats In Pool Construction

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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

Swimming Pool Expert Witness

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Swimming Pool Expert Witness - Paolo Benedetti

Indoor Pools & Water Vapor, What You Need To Know

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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.

Swimming Pool Expert Witness

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