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Below-ground tanks leak out when full and let groundwater or dirty water seep in when empty. Plug and repair, then line the inside with a drinking-water coating; on new tanks, build watertight concrete and joints first.
General guidance based on the manufacturer data sheets. Site conditions differ: confirm the system with MCT before you start. Where we do not name a product, ask us and we will confirm the right one.
Before the pour, add a waterproofing admixture: SikaControl-760 lists water tanks and reservoirs (p.1). Cast a Sika Waterbar V-20 L SH into construction joints (reservoirs, p.1), or place SikaSwell S-2 in the centre of the wall with at least 8 cm cover each side; it is not for movement joints (SikaSwell S-2 p.2). Coat the outside face against aggressive soil with Sika Bitumen (p.1). These sit inside or outside the concrete; the drinking-water face is still lined in a later step.
SikaControl®-760 should be used in all structural concrete that is constantly or intermittently in contact with water such as sea walls, tunnels, basements, structural and precast concrete. SikaControl®-760 can also be used as crystalline waterproofing admixture for cement mortars and plasters. T… (TDS p.1)
Sika Waterbar® V-20 L SH is used to waterproof construction joints in concrete structures such as those in water retaining structures, including reservoirs, canals, sewage plants, dams, swimming pools etc. (TDS p.1)
The right product here depends on your site. We confirm it before naming it.
Drain and ventilate the tank before anyone enters. Remove sludge, laitance and old coatings by water jetting or wire brushing (SikaTop-550 Seal p.3). With the tank empty, note where groundwater comes in. If a septic tank or soakaway is close by, have the drainage checked as well.
Plug running holes and static cracks with SikaSet Waterplug (NSF/ANSI 61 for potable water contact, p.1). Water-bearing cracks and leaking joints are injected with Sika Injection-306, which works in damp or water-saturated ground (p.1). It is for experienced professionals only (p.1), and nearby drains and open pipes must be checked first (p.2).
Non-moving (static) cracks and holes with running water or moisture seepage For immersion service For anchoring vertical bolts Basements Foundations Retaining walls Sewers Locations Vertical, overhead, or horizontal Interior or exterior Above or below grade… (TDS p.1)
Crack and joint injection Injection of SikaFuko® injection hoses to seal construction joints Sealing water-bearing cracks and voids Sealing all types of leaking building components in damp or water saturated ground conditions Sealing leaks where there is so… (TDS p.1)
Rebuild spalled or honeycombed areas with a SikaRep or MonoTop repair mortar (SikaTop-550 Seal p.3). Above 35 °C, use chilled mixing water (Sika MonoTop-612 PK p.2). Close blowholes with a pore sealer (SikaRep Fine PK p.1).
The right product here depends on your site. We confirm it before naming it.
SikaTop-550 Seal (BS 6920, p.1) is breathable and is applied on a pre-dampened surface (p.1, p.3), so it suits walls that stay damp from the soil. Sikagard PW (potable, p.1) must not be applied on substrates with rising moisture (Sikagard PW p.3), so use it only on dry, sound concrete and only by experienced professionals (p.1).
As a waterproof lining for water retaining structures. (TDS p.1)
Chemical resistant protective layer on concrete, structural cementitious mortars, epoxy cement, epoxy resin based products and steel Protection of concrete surfaces / foundations below ground level Lining in storage tanks, manholes, intakes and silos etc. (TDS p.1)
Seal joints and gaps around pipes with Sikaflex PRO-3 WF (BS 6920 drinking water contact, p.1), primed as the data sheet requires for water immersion (p.4). Never use polysulphide sealants (Sika Polysulphide GG p.2) or Sikaflex Tank N (p.1) in a drinking-water tank.
Sikaflex® PRO-3 WF is designed for movement and connection joints in floors, pedestrian and traffic areas (e.g. (TDS p.1)
Protect the fresh lining from water and condensation as its data sheet requires (Sikagard PW p.3: at least 24 hours). Clean and disinfect to local rules before refilling (Sikagard PW p.3).
A starting point for a site proposal. Quantities, prices and the final specification follow a site visit or photos.
| Step | Product | Pack | Source |
|---|---|---|---|
| 1. New tanks: watertight concrete and joints | SikaControl-760 | SikaControl®-760 is available in 5 Kg & 25 kg pack. | TDS p.1 · March 2025, Version 04.01 |
| 1. New tanks: watertight concrete and joints | Sika Waterbar V-20 L SH | — | TDS p.1 · May 2021, Version 01.01 |
| 3. Stop active leaks | SikaSet Waterplug | — | TDS p.1 · September 2024, Version 02.01 |
| 3. Stop active leaks | Sika Injection-306 (professionals) | — | TDS p.1 · May 2021, Version 02.01 |
| 5. Line the inside with a drinking-water coating | SikaTop-550 Seal | — | TDS p.1 · March 2024, Version 01.01 |
| 5. Line the inside with a drinking-water coating | Sikagard PW (professionals) | — | TDS p.1 · May 2021, Version 02.01 |
| 6. Seal joints and pipe entries | Sikaflex PRO-3 WF | — | TDS p.1 · May 2021, Version 02.01 |
Running leaks are first plugged (SikaSet Waterplug p.1) or injected (Sika Injection-306 p.1). The SikaTop-550 Seal data sheet does not state resistance to water pushing from behind, so for a high water table, Ask us: it depends on site conditions.
Their data sheets list water tanks (SikaTop-107 Seal PK p.1; SikaSeal-105 PK p.1) but do not state drinking-water approval. We use them only for non-drinking tanks, such as fire or irrigation storage. For drinking water we use SikaTop-550 Seal or Sikagard PW (06 F2).
Fix the drainage first. No coating data sheet covers sewage contamination of a drinking-water tank, and injection also needs a survey of nearby drains and open pipes (Sika Injection-306 p.2). Ask us: it depends on site conditions.
SikaTop-550 Seal can be applied to 24-hour-old concrete (p.1). Sikagard PW needs sound concrete of at least 25 N/mm² and no rising moisture (p.3).
Steps and product facts are taken from the manufacturer data sheets (page cited). Products are named only where the data sheet confirms the use; quantities follow a site visit or photos. General guidance: check the data sheet or ask us before you start.