Concrete Tank Cleaning in Riyadh

Lime scale (calcium carbonate) is deposited by hard water itself. It shows as a grey or white crust at the waterline, on the floor and around pipe outlets, and grows thicker wherever water evaporates or its surface moves. It comes off by soaking, brushing and pressure, and it signals hardness in the supply, not a fault in the tank.

Efflorescence has a different source: salts travelling from inside the concrete wall or from the soil behind it. It appears as fine white powder or needle-like threads above the waterline, or on the outer face of a below-ground wall. It means moisture is crossing the wall and evaporating at the surface, so if it returns in the same place within weeks the issue is a moisture path, not dirt.

Two other things get confused with these: the slimy green or brown film, which is biological and goes with cleaner and brushing, and orange rust streaks, which come from reinforcement close to the surface or from metal fittings and mean the concrete cover over the steel is thin or damaged. We separate the four at the visit because each carries a different remedy and a different warning.

• Lime scale: hard crust at the waterline and on the floor
• Efflorescence: fine white powder above the waterline
• Biofilm: slimy green or brown layer
• Rust: orange streaks near the reinforcement

We start with the gentlest option: wetting the wall thoroughly first, because wet concrete absorbs less of the descaler and tolerates abrasion better. Then nylon or stiff bristle brushing on thin crust, then rinsing. What clears at this level is not escalated to a harsher method, because every step up takes some of the concrete face with it.

For thick scale we use pressurised water with a rotary or fan head, held at a steady distance and angle after a trial on a small patch. Very high pressure digs out the cement paste and exposes aggregate, leaving a rougher wall that catches scale faster, and it lifts hollow render and washes filler out of joints. So pressure is set by the hardness of the surface, not by a wish to finish sooner.

The last step is a mild descaler applied locally to leftover crust, after wetting the wall and with continuous ventilation, then neutralised and rinsed out completely. Acids dissolve scale but also dissolve cement paste, release carbon dioxide in a confined space, and must never be mixed with chlorine. That is why this step stays local and time-limited.

Concrete is not smooth like fiberglass. It has capillary pores, the roughness of render and small voids that water enters carrying minerals and microscopic algae. Washing pulls out what sits in the surface layer, but it does not close the pores. That is why scale and biofilm return faster on an old rough wall than on a smooth new one.

This explains why a tank looks clean after the wash and the scale comes back in the same place within months. It is not a fault in the work but the nature of the surface. What good cleaning achieves is removing the whole stock of deposits at the time of the wash, exposing the true sound surface, and giving the owner an honest picture of porosity and bond, which is worth more than a clean wall whose condition beneath is unknown.

If the owner wants a smoother surface on which deposits form later, the answer is a waterproofing layer or a coating made for drinking water, and it has its conditions: a clean, dry and sound wall. We prepare that surface by washing and identify what needs treatment, while the application itself is covered on the concrete tank waterproofing page. We do not recommend coating over scale, whatever the coating.

Once the silt and scale are gone, the walls show their true state: fine lines spread like a net, usually surface shrinkage in the render; straight vertical or horizontal cracks following the reinforcement or a joint; honeycombing and voids in the pour; and a wall-to-floor or pour-to-pour joint that looks damp. Not every line is a crack that leaks.

We handle a finding in set steps: locate it precisely, photograph the crack beside a ruler, mark both ends with pencil and date so the owner can see if it moves, and check for white deposits beside it or dampness on the other side. We do not chase out the crack or fill it with cement paste during the wash, because filling over a wet or moving surface fails quickly.

Then we classify: surface-level, which a coating or waterproofing layer can cover; leaking, which needs injection; or wide and advanced, which needs an engineer's opinion before any waterproofing. That classification decides what follows and is what the concrete tank waterproofing page deals with. For an underground tank where you suspect a leak, the underground tank waterproofing page is the reference.

A below-ground concrete tank is a confined space, often with a single opening, and the air inside can be low in oxygen or carry gas. So we open the lid early and let it ventilate, add forced ventilation where needed, and nobody enters until the supervisor has checked the air and there is a second person at the opening who watches and can pull them out.

Field rules include low-voltage lighting that will not electrocute anyone in wet conditions, submersible electric pumps and no petrol engines near the opening because their exhaust carries carbon monoxide that drifts inside, a fixed ladder, non-slip boots because silt and film are slippery, and never mixing cleaners and descalers inside because some mixtures release toxic gas.

On the owner's side: do not stand around the open manhole, keep children and pets away, and do not climb down to help or check the work. Viewing the photos and the technician's notes when the job ends is safer and clearer than looking in from the opening, and gives you what you need for the waterproofing or repair decision. If other workers or neighbours are around, warn them about the open manhole.