Waterproofing of tanks, swimming pools and treatment plants

What this section covers

This section covers materials for concrete liquid-retaining structures: clean and drinking water tanks, fire water and process water tanks, pressure and distribution chambers, swimming pools and fountains, channels and flumes, water treatment works and sewage treatment plants. What they have in common is permanent or intermittent contact with water, often under pressure, and, for drinking water, hygiene requirements for the material as well.

Internal linings for steel tanks and pipelines are covered in the “Coatings for tanks and pipelines” section, and vessels and bunds for acids, alkalis and oxidisers in the “Chemical protection” section.

Features of liquid-retaining structures

Pressure from both sides. The water in the tank pushes from the inside and the groundwater from the outside, especially when the tank is emptied for repair or flushing. That is why the permissible negative pressure also matters for the internal lining: for the polymer-modified cementitious Fosroc Nitocote CM210, according to its data sheet, it is 3 bar against 7 bar positive, and for the osmotic mortar Mapei Planiseal 88 up to 1 atm.
Permanent immersion. The material must be designed specifically for it: many roofing membranes and hybrid polyureas are not intended for immersion.
Hygiene. For drinking water, documents for contact with water are needed — for the coating itself and for all ancillary materials that remain in the tank.
Structural movement. Thin-walled and elevated tanks and tanks on collapsible soils are subject to deformation. Rigid coatings crack on such structures: the Fosroc Nitocote CM210 data sheet, for example, explicitly excludes elevated tanks and other structures with large movements.
Abrasion and cleaning. In channels and flumes, the water carries sand, and swimming pools are cleaned regularly, sometimes with pressurised water; this is taken into account when choosing the material and the thickness.
Gas zone. At treatment plants, the most aggressive zone is often not the water but the space above it, where hydrogen sulphide is converted into sulphuric acid on the concrete surface.

Materials for tanks

Watertight concrete and crystalline admixtures. The basis of any tank is dense concrete with the water impermeability grade specified in the design. Crystalline admixtures and penetrating compounds densify it and work from either side; the Xypex and Penetron data sheets state NSF 61 approval for contact with drinking water — under the North American standard now designated NSF/ANSI/CAN 61. For more details, see the “Penetrating waterproofing” section.
Polymer-modified cementitious and osmotic coatings — Fosroc Nitocote CM210, Mapei Planiseal 88: applied to damp concrete, vapour-permeable, withstand pressure on the positive side and, within specified limits, on the negative side. These are rigid coatings for structures without significant movement.
Flexible cementitious compounds — for channels, tanks and swimming pools with cracks and deformations: Mapelastic Smart, SikaTop-525 Seal (see “Cementitious waterproofing”).
Solvent-free epoxy coatings — a smooth, easy-to-clean surface, resistance to chlorinated water and wastewater according to the data sheet. Fosroc Nitocote EP405 is applied to dry or damp concrete in two coats of contrasting colours, but running water must be excluded throughout application and curing.
Polyurea — a seamless, thick lining with rapid return to service: Fosroc Polyurea WPW is designed for clean drinking water up to 60 °C, and according to its data sheet the tank can be filled just 24 hours after flushing. Only pure polyureas permitted by the data sheet are suitable for immersion (see “Polyurea”).
Joints. Construction joints are dealt with using waterstops, swelling profiles and injection hoses (see “Joint waterproofing”), and movement joints with waterstops and elastic sealants for immersion, for example Fosroc Nitoseal MS600, which accommodates 25 % joint movement and is approved for contact with drinking water.

Drinking water

The lining of a drinking water tank must be not only watertight but also safe for the water. Foreign approvals — the North American standard NSF/ANSI/CAN 61, British, German, Italian and other national schemes — confirm the properties of the material but do not replace the documents required in the country of use. Their availability for Uzbekistan and other Central Asian countries is checked before ordering.

Documents are needed for the whole system, not just for the main layer: primers, repair mortars, sealants, products for joints. If an ancillary material has no approval, it is completely covered over — for example, the Fosroc Polyurea WPW data sheet requires that the primers and the product used at day joints do not come into contact with drinking water. Before commissioning, the lining is left for the required period, then washed and flushed according to the manufacturer’s instructions: according to its data sheet, Planiseal 88 is put into service after 7 days, and after setting the surface is thoroughly washed and all the wash water is removed.

Treatment plants and wastewater

ShNK 2.03.11-24 requires reinforced concrete structures of wastewater facilities with an aggressive gaseous environment inside to be made of concrete of at least class B30 with a water impermeability grade of at least W8, and sewer pipes, manholes and chambers in locations with an aggressive environment to be protected with chemically resistant silicate, polymer and other materials. Protection is selected separately for the zone of permanent immersion, the zone of fluctuating level and the gas zone above the water. The material is checked for suitability for such an environment: the Sikalastic-841 ST data sheet, for example, explicitly excludes enclosed tanks where attack by biogenic sulphuric acid is possible. Resistance to the specific medium is confirmed by our questionnaire: substance, concentration, temperature and regime.

Swimming pools

A pool shell is a vessel with chlorinated water, temperature fluctuations and regular cleaning. Under tiles and mosaics, cementitious waterproofing products tested to EN 14891 are used, including for bond after contact with chlorinated water; cast-in items, drains, inlets and joints are covered with the system tapes and collars. The tile adhesive and grout are taken from the same system. Exposed polymer coatings for pool shells are chosen for the resistance to chlorinated water stated in the data sheet, bearing in mind that many epoxies change colour in the sun.

Sequence of work

A survey and, if the design provides for it, a water test of the tank: it reveals the joints, cracks and penetrations that need to be sealed before lining.
Stopping active leaks, injecting cracks and joints, repairing honeycombing and deteriorated concrete — with products approved for drinking water if the tank holds drinking water.
Surface preparation for the selected material: removal of laitance, contamination and old coatings, the required roughness; fillets at internal corners. Cementitious products are applied to water-saturated concrete, polyurea to dry concrete with at least the strength required by the data sheet: for Fosroc Polyurea WPW, at least 75 % of the design strength.
Details: joints, pipe penetrations, cast-in items — before the continuous layers.
Application of coats in contrasting colours, with checks on consumption and thickness, so that any misses can be seen.
Curing until full cure, washing and flushing, putting into service within the times given in the data sheet. The Fosroc Nitoseal MS600 sealant, for example, is cured for 21 days at a temperature of 7 °C or above before immersion in drinking water, and for at least 7 days before immersion in wastewater.

Common mistakes

A material for a drinking water tank without documents for contact with water, or with primers and repair mortars that are not approved.
A coating designed only for the positive side in a tank that is pressed by groundwater from outside — delamination when the tank is emptied.
A rigid coating on a thin-walled or elevated tank subject to movement.
Only the water zone is protected, and the gas zone of the treatment plant is left unprotected.
Joints and pipe penetrations were not dealt with before lining — leaks bypass the coating.
The tank was filled before the end of the curing period, without washing and flushing.
The sealant is not designed for permanent immersion or is incompatible with adjacent materials — for example, an MS sealant in contact with bitumen.

Materials in the catalogue

Planiseal 88 — Mapei — osmotic cementitious mortar for drinking water tanks and basements, formerly Idrosilex Pronto.
Fosroc Nitocote CM210 — Fosroc — polymer-modified cementitious waterproofing for water tanks and reservoirs, WRAS approved.
Fosroc Polyurea WPW — Fosroc — hot-spray pure polyurea lining for drinking water tanks, WRAS listed to 60 °C.
Fosroc Nitocote EP405 — Fosroc — solvent-free epoxy lining for tanks and water treatment works, potable water approved.
Fosroc Nitoseal MS600 — Fosroc — one-part MS polymer sealant for joints under permanent immersion, potable water approved.

Frequently asked questions

Which coating should be chosen for a drinking water tank?

It depends on the condition of the concrete, the groundwater pressure from outside, the acceptable downtime and the documentation requirements. For a new cast-in-situ tank, watertight concrete with a crystalline admixture and properly detailed joints is often enough; for an old one — a penetrating or polymer-modified cementitious compound, an epoxy lining or polyurea. In any case, documents for contact with drinking water that are recognised in the country of use are required.

Can a tank be lined without emptying it?

No: linings are applied to a prepared surface without running water and are left to cure. Without emptying, only certain repair operations from the outside are possible, for example injection.

Will waterproofing help against condensation on the walls of a pump room or chamber?

No. Condensation results from differences in temperature and air humidity, and it cannot be eliminated with a waterproofing compound: this is stated explicitly, for example, in the Planiseal 88 data sheet. Ventilation, insulation or dehumidification is needed.

Does a tank need to be protected from the outside?

If the tank is buried and stands in groundwater, as a rule, yes. For structures in contact with aggressive groundwater or soil, ShNK 2.03.11-24 explicitly requires the side surfaces to be protected, taking into account a possible rise in the water level and an increase in its aggressiveness over the service life.

We will select a waterproofing system for your tank, swimming pool or treatment plant and calculate the supply — call us or message us on WhatsApp/Telegram: +998 94 094 52 27.