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.
