June 1, 2013
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|
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 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.
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.
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.
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 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.
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.
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.
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.
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.
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 (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)
Day two (brush the pool)
Days four to 28
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.
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.
Peter 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 email@example.com.
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