Water care for a cement-based pool finish: from first fill to routine

Practical guidance for architects, pool builders and operators on filling, start-up, water balance, hot-climate management and surface troubleshooting for cement-based exposed-aggregate pool finishes.

Water care for a cement-based pool finish begins before first fill. It continues through a structured first-month start-up and then becomes routine testing, brushing and record-keeping. Pool water is always in contact with a cement-based finish, so keeping pH at 7.6 to 7.8 and balancing alkalinity, calcium hardness and sanitiser helps reduce the risk of etching and scale. Staining needs separate investigation. The water chemistry requirements are the same for PebbleCrete Classic, PebbleCrete Supreme and PebbleCrete Glass.

Filling-water quality and clean filling

A pool finish is always seen through water, and its condition starts with the first fill. The finish is decorative. It is not structural repair or waterproofing, so shell repairs, waterproofing and water testing must be completed and accepted before application begins.

Before the finishing visit, inspect the water source, storage tanks, balance tanks, sumps and delivery hoses. Clear construction dust, slurry and debris from the pool and circulation areas so that nothing washes back in when the pumps start. Never put dirty or muddy site water into a newly finished pool.

Water that looks clear may still be unsuitable. In Southeast Asia, water from wells, rivers or lakes can arrive at pH 5.5 or carry dissolved iron and copper. Test the filling supply in advance, keep the results so you can assess staining risk, and agree the start-up plan with the project team.

Why the first weeks matter

Follow the approved filling and start-up programme from the moment the installer releases the completed pool. Filling should begin promptly and continue without interruption.

Three rules apply during the first month:

• Daily brushing and continuous filtration: Run filtration continuously and brush the whole pool daily for the first month. Brush twice daily in the first week if the start-up programme specifies it.
• Delaying salt for 28 to 30 days: On salt-chlorinated pools, do not add salt at first fill. Wait 28 to 30 days, then follow the written start-up and chlorinator instructions.
• Preventing direct chemical contact with the finish: Never let chlorine granules, tablets or liquid land directly on the finish, because direct contact can leave irreversible marks. Add all chemicals as set out in the product labels, the equipment instructions and the approved operating programme.

Main water parameters to keep balanced

PebbleCrete’s aggregate contains no calcium; the cement matrix that holds it does. Water that is acidic or short of calcium can dissolve minerals from cementitious surfaces. Read all the parameters together rather than relying on single readings.

The figures below are PebbleCrete care targets. They apply subject to any commercial-pool requirements in force and to the pool’s approved treatment programme.

• pH (Target: 7.6 – 7.8; working range: 7.2 – 7.8): A unitless measure of acidity and alkalinity. Below 7.6, the water becomes more likely to draw calcium from the cement matrix. Keep pH at the specified level and keep monitoring every other required parameter.
• Total alkalinity (Target: 80 – 120 ppm): The buffer that resists pH changes and limits daily swings.
• Calcium hardness (Target: 200 – 400 ppm): Dissolved calcium in the water. Assess it together with pH, alkalinity and temperature when judging the risk of etching and scale.
• Free chlorine (Target: 1 – 3 ppm for every system): The active disinfectant in the water. Liquid chlorine and trichlor are dosed intermittently, while salt chlorinators produce chlorine continuously. A chlorinator’s percentage setting is an equipment setting, not a water test reading. UV or ozone systems do not justify lower sanitiser levels without an approved basis.
• Cyanuric acid (Target: 30 – 50 ppm) and salinity (within the chlorinator range, typically 3000 – 4500 ppm): Above roughly 50 ppm, stabiliser increasingly reduces chlorine effectiveness unless free chlorine is raised accordingly. Keep salinity within the chlorinator manufacturer’s range.
• Saturation index (for example, the Langelier index): One tool for judging whether water tends to form scale or dissolve the surface. Use it alongside full test results. It does not measure disinfection or staining risk.

Hot climates: evaporation, top-up water and hotel bather loads

In the hot climates of Southeast Asia and the Middle East, high evaporation removes pure water and leaves dissolved calcium, salts and stabiliser behind, so they become more concentrated. Frequent top-ups also change the chemistry. Top-up water can change hardness and alkalinity, depending on what testing shows it contains. Acidic borehole, well or rain-fed water may affect pH and alkalinity. Test the source and monitor the pool after each top-up.

High hotel and resort bather loads increase sanitiser demand. Trichlor tablets are common in Southeast Asia and can be used with a PebbleCrete finish if the water is monitored. Every tablet lowers pH and adds cyanuric acid, so switch to liquid chlorine as stabiliser approaches 50 ppm.

With salt chlorination, pH tends to drift upward. A cement-based finish tolerates that direction better, but rising pH also increases scale risk. Monitor regularly and adjust within the approved targets. Size salt chlorinators with peak bather load in mind; actual dosing should still follow water testing and the approved programme.

Scale, staining and colour change: causes and investigation

Investigate any surface change before cleaning or repairing it. The first step is to tell material deposited on the surface apart from material lost from it.

• Etching and roughness: In the cases PebbleCrete sees in Southeast Asia, early wear is often linked to three habits: filling with low-pH well or river water, adding trichlor without correcting pH, and testing only chlorine and pH. Etching wears away the cement surface, so the aggregate stands proud and feels rough. If left untreated, aggregate can eventually come loose. Correct the water chemistry first. A specialist must then assess the repair options. A nominal 10 mm thickness alone does not show that polishing is suitable or what appearance can be achieved.
• Scale and white deposits: White crusts on the interior, or along tiled and polished aggregate waterlines, may be linked to high pH, too much calcium hardness or mineral build-up from evaporation.
• Staining and colour change: Local marks or colour shifts may be linked to iron or copper in fill water, corroding wall fittings, rust bleeding from cracks, dried construction run-off or direct chemical contact. These links do not prove a cause. Check the water history and identify which layers are affected.

Record when the change appeared, whether it is spreading and whether the pool is losing water. Take overall and close-up photographs, check whether marks line up with fittings or water levels, and review the water logs. Never use concentrated acid washing as a maintenance shortcut. Strong acid can damage cementitious finishes, and it cannot remove an active stain source or fix a substrate fault beneath the finish.

Routine brushing and records worth keeping

As a planning figure, an exposed-aggregate pool finish is generally expected to serve for 15–20 years. This is an industry estimate, not a warranty term. Where an individual pool falls within or outside that range depends on substrate preparation, application quality, water chemistry and routine maintenance.

After the first month, brush walls, steps, corners and low-flow zones regularly. Brushing helps remove settled debris and keeps the surface clean, alongside effective circulation and disinfection. Keep the operating water level within the waterline band designed to be cleaned. Back up physical care with a written operating record, and review it as a sequence over time:

• Test readings: Date, time, test method and readings. Record pH separately from ppm values.
• Treatment changes: Chemicals and amounts added, with readings before and after, plus filter cleaning and equipment adjustments.
• Water sources, events and observations: Fill-water tests, heavy rain, top-ups, high bather loads, nearby building work, circulation stops and dated photographs of surface changes.

When the pool passes to a new operator, hand over the finish identification, care instructions, equipment details and the start-up log.

In Thailand: Pebble Pools (pebblepools.co.th) offers water filtration and restarting a pool after a long shutdown. Their local guide: borehole water and pool stains.

Frequently asked questions

Photographs and screen colours are illustrations. Confirm colour and texture with a current physical sample viewed wet and an approved on-site mock-up.

More in the Knowledge Centre ↗ · Ask a technical question ↗