Maintenance and application techniques for cement-based pool finishes

June 1, 2013

Chimera Pool & Landscape, LLC[1]
Exposed aggregate finishes are mixed with cement and water and have proven to be a reliable and esthetically pleasing pool finish as they have a natural appearance and are available in a wide range of colours.

By Peter Vamvakaris

Plaster is defined as a soft mixture of lime, sand or cement, and water. It is common for contractors and swimming pool owners alike to associate all cement-based interior pool finishes as a plaster finish; however, this is not the case.

Plastering is the action of coating or covering a surface with a substance. For pools, these substances can range from a variety of cement-based finishes such as plaster (i.e. marbelite), quartz crystals, pebble, and glass beads. All of these finishes are mixed with white cement and water, and are either hand-trowelled or pneumatically applied onto the pool surface. As opposed to plaster and quartz finishes, where the cement cream is brought up to the surface to create a smooth finish, pebble and glass-bead finishes are left exposed by removing the top layer of cement cream to reveal the coloured pebble/glass. Pebble finishes can also be polished, and depending on the brand, some smaller pebbles can be buffed.

When it comes to selecting a pool finish, beauty and longevity are the two main considerations in the decision making process. Although beauty cannot be measured on a scientific scale, longevity—based on the materials used—can be. Interior pool finishes comprise two primary materials: cement and aggregate. All aggregates are minerals (i.e. pure substances found in nature) that are characterized by the Mohs scale of mineral hardness.

Mohs hardness Mineral Absolute hardness
1 Talc 1
2 Gypsum 3
3 Calcite 9
4 Fluorite 21
5 Apatite 48
6 Orthoclase Feldspar 72
7 Pebble Quartz 100
8 Topaz 200
10 Diamond 1600

Plaster (marbelite)

Plaster is an economical finish, which comprises white cement, marble aggregate, and water. This finish provides a traditional swimming pool look; however, it is important to know that white plaster is the most susceptible to improperly maintained or fluctuating chemical conditions. Therefore, it is only reasonable to expect its appearance to change during the life of the product. It is important for builders to be fully aware that plaster is a relatively soft finish with a rating of three on the Mohs hardness scale, with an absolute hardness rating of nine.

Quartz (100 per cent)

Quartz finishes comprise white cement, 100 per cent quartz, and water. These finishes are durable and create a much denser surface compared to standard plaster, making it harder and far more resistant to fluctuating chemical conditions. A broad range of colours are available as well.

While there are other formulations of quartz available (e.g. 10, 25 and 50 per cent), the full benefits cannot be achieved unless a 100 per cent quartz aggregate is used as it has a rating of seven on the Mohs hardness scale, with an absolute hardness rating of 100.

Pebble/exposed aggregate

Pebbles are embedded throughout an exposed aggregate finish, which is also mixed with cement and water. These finishes have proven to be the most reliable and esthetically pleasing on the market today as they have an extremely natural appearance and are available in a wide range of colours.

Black_Onyx[2]
Pebble aggregates are rated seven on the Mohs scale with an absolute hardness rating of 100.

As the pebble is exposed in a wash process, the stone material that comprises the pebble is chemically inert; therefore, the finish will not react to varying pool/spa water conditions, making it less susceptible to attack or alterations in appearance.

Licensed Applicator[3]
A licensed applicator shoots the pebble finish via a remote wand system and slurry pump.

Pebble aggregates are rated seven on the Mohs scale with an absolute hardness rating of 100, making this finish more than 10 times harder than a traditional plaster finish. That said, these finishes should be applied by a trained technician.

Glass beads

Glass beads are a unique architectural pool finish that creates added light refraction. These finishes contain small, reflective solid-glass spheres that are locked into an aggregate mix of polymer modified cement. They are combined with selected coloured aggregates, which mirror light under the surface of the pool’s water and create a vibrant, sparkling finish.

Similar to exposed aggregate, glass bead finishes should be applied by a professional.

Water_Blue[4]
Depending on the type of glass, the Mohs hardness scale rating will vary between five and seven, while the absolute hardness rating can fluctuate between 45 and 100.

Depending on the type of glass, the Mohs hardness scale rating will vary between five and seven, while the absolute hardness rating can fluctuate between 45 and 100.

Reef Tropical Pools[5]
Glass beads are a unique architectural pool finish that creates added light refraction via small, reflective solid-glass spheres that are locked into the aggregate mix of polymer modified cement.

Pricing for interior pool finishes will vary depending on the material used and application process; therefore, ask the applicator about their processes and warranty. Be wary of the lowest price as taking shortcuts can affect the quality and longevity of the pool’s finish.

Application techniques

To apply a cement-based pool finish, it is important to follow the manufacturer’s directions. There are two ways to apply a pool finish, manually (i.e. by hand) or pneumatically with a pumping rig.

Hand-finished

Applying a pool finish manually typically requires a 0.1-m3 (6-cf) mobile mortar mixer, which is capable of making approximately 180- to 226-kg (400 to 500 lbs) batches of pool finish materials. Generally, the mixer is placed as close to the pool as possible, making it easier to pour the wet mix into a wheel barrow, where it is then shoveled into buckets and carried into the pool for application. At this point, labourers supply small amounts of the mixture from the plasterers ‘hawk’ (i.e. a tool used to temporarily hold the plaster) to their trowel to apply the mixture onto the pool surface.

Manually applied pool finishes should be completed by highly skilled operators as the potential for cold joints (i.e. the juncture of fresh stucco application adjacent to set plaster) and inconsistent batches (mixes) can affect the finished appearance.

Mechanically applied

Applying cement-based pool finishes with a pumping rig involves using a large flatbed truck that has been specifically designed and equipped with a large, 0.33- to 0.39-m3 (12- to 14-cf) mixer, with an integrated hopper and pump.

This rig allows more than 453 kg (1,000 lbs) of pool finish material to be mixed at one time, reducing the total number of batches required to complete a pool project. Large, 51-mm (2-in.) hoses are connected to the manifold of the pumping rig, which would be parked on the street to eliminate any damage or mess to the customer’s property.

The mixture is then sprayed onto the pool surface, creating a mechanical bond by the pressure of which the material ‘shoots’ out of the hose. Although traditional marble-based finishes can be placed manually or pneumatically, higher quality pebble- and glass-bead finishes can only be installed via custom configured pumping rigs with specialized pumps.

PLASTER POOL START-UP PROCEDURES
With any cementitious-based finish, swimming pool start-up and maintenance procedures are key; following the recommendations of the National Plasterers Council [6](NPC) can assist in this process.
Cement-based finishes generally begin to hydrate immediately after mixing, with the majority of hydration taking place within the first 28 days. This critical time period is when the finish is most susceptible to staining, scaling, and/or discolouration. Therefore, proper start-up procedures, including timely pool brushing, and constant monitoring and adjusting of the pool water is mandatory.
The following recommended start-up method is based on procedures shown to produce the best esthetic results. Due to unique local water conditions and environmental factors, parts of these procedures may need to be modified to protect the pool finish. (For example, filling the pool with water containing extremely low calcium hardness, pH, or total alkalinity (TA) levels may necessitate changes to these procedures. Brushing and monitored chemical adjustments will be mandatory by the homeowner, or a trained pool technician, during the service life of any pool surface.Pool filling day
1. Make sure the filtration equipment is operational.
2. Remove all pool floor return heads and directional eyeballs (if appropriate and recommended as per the geographical area).
3. Based on temperature and pool finish type, fill the pool to the middle of the skimmer or other specified water level as rapidly as possible and without interruption using clean potable water to help prevent bowl ring. Cover the end of the hose with a clean rag and place the nozzle in the deepest point of the pool to prevent damage to the surface material. If a water truck is required, the pool’s deep end should be pre-filled with approximately 0.6 m (2 ft) of water to provide a water cushion. Further, wheeled devices should not be used in the pool until after the 28-day start-up has been completed.
4. Also, at no time should any person or pets be allowed in the pool during the fill. To help prevent streaking, do not allow any external sources of water to enter the pool. Further, it is recommended no one swims in the pool until the water is properly balanced.
5. Test the parameters of the fill water (e.g. pH, alkalinity [TA], calcium hardness, and metals). Be sure to record all test results.
6. Start the filtration system immediately when the water level reaches the middle of the skimmer or other specified level.

Day one (after filling the pool)
1. It is vital to follow these steps in order prior to proceeding to ‘day two.’
2. Test the water’s pH, alkalinity (TA), calcium hardness, and metals. Record all results.
3. High alkalinity should be adjusted to 80 parts per million (ppm) using pre-diluted muriatic acid (31 to 33 per cent hydrochloric acid). Always pre-dilute the acid by adding it to a 19-L (5-gal) bucket of pool water.
4. Low alkalinity should be adjusted to 80 ppm using sodium bicarbonate (NaHCO3) (baking soda).
5. Reduce the water’s pH to 7.2 to 7.6 by adding pre-diluted muriatic acid if the alkalinity is already between 80 to 100 ppm.
6. Brush the entire pool surface thoroughly at least twice daily to remove all plaster dust.
7. Although optional, adding a pre-diluted quality sequestering agent is highly recommended. When adding, use the recommended initial start-up dosage and then the manufacturer’s recommended maintenance dosage.
8. Operate the filtration system continuously for a minimum of 72 hours.
9. Do not add chlorine (Cl) for 48 hours, and do not turn on the pool heater until all signs of plaster dust have been removed from the pool.

Day two (brush the pool)
1. Test the water’s pH, alkalinity (TA), and calcium hardness, repeating steps one through five (leaving out step six) from ‘day one.’
2. Once the alkalinity (TA) is adjusted to 80 ppm and the pH is adjusted to 7.2 to 7.6, adjust the calcium hardness level to a minimum of 150 ppm. (Note: Adjustments requiring more than 9 kg [20 lbs] of calcium chloride [CaCl] should be pre-diluted and added in 4.5 kg [10 lbs] increments, e.g. morning and afternoon.)

Day three
1. Test the water’s pH, alkalinity (TA), and calcium hardness, repeating steps one through six from ‘day one.’
2. Pre-diluted chlorine can now be added to achieve a level of 1.5 to 3 ppm. No salt should be added for 28 days.
3. Brush the entire pool surface thoroughly (at least twice daily) to remove all plaster dust.

Days four to 28
1. Test the water’s pH, carbonate alkalinity, and calcium hardness, repeating steps one through five from ‘day one’ for the next 14 days to help prevent pool surface scaling.
2. If plaster dust remains on the seventh day, remove it using a pool brush vacuum.
3. After the fourth day, calcium levels should be adjusted slowly over the 28-day period not to exceed 200 ppm.
4. Also after the fourth day, adjust cyanuric acid (CNOH)3 levels to 30 to 50 ppm based on the pool’s primary sanitizer. Pre-dissolve and add through the skimmer.

The NPC also offers start-up technician courses to certify pool service personnel. Upon completion of the 28-day start-up, water chemistry and maintenance should be monitored and balanced as per NPC guidelines.

Conclusion

When choosing a cement-based pool finish, consider the hardness of the material used as well as its warranty and application procedures. Keep in mind, as the material of choice moves up the Mohs scale of mineral hardness, the price point will also increase. More importantly, however, application superiority and quality control will determine the beauty and longevity of a cement-based pool finish.

 

Vamvakaris_HeadshotPeter Vamvakaris is the operations manager for Pebble Tec Canada, Canada’s first appointed installer of Pebble Technology International’s line of swimming pool finishes. He is a second generation pool finisher and an active member of the National Plasterers Council (NPC). He can be reached via e-mail at peter@pebbletec.ca[7].

Endnotes:
  1. [Image]: http://psm.poolspas.ca/wp-content/uploads/2013/06/Chimera-Pool-Landscape-LLC.jpg
  2. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Black_Onyx.jpg
  3. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Licensed-Applicator.jpg
  4. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Water_Blue.jpg
  5. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Reef-Tropical-Pools.jpg
  6. National Plasterers Council : http://www.npconline.org
  7. peter@pebbletec.ca: mailto:peter@pebbletec.ca

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