What is White Tank Waterproofing?

Watertight concrete is made with a low water-cement ratio and a suitable mix. It therefore has few continuous capillary pores, and water only penetrates the element to a limited depth. The wall stays dry on the room side as long as it is thick enough and has no water-carrying cracks.

The real weak points lie elsewhere:

• Construction joints between floor slab and wall and between pours – secured with joint sheets, waterstops or injection hoses.
• Penetrations for utility connections, sewage and cables – sealed with pressure-tight sleeves and annular seals.
• Through-cracks, which can form from shrinkage and temperature differences while the concrete sets.

The WU guideline requires two things to be defined up front:

• Stress class (Beanspruchungsklasse) – how water acts on the structure. Class 1: pressing and non-pressing water and temporarily accumulating seepage water. Class 2: soil moisture and non-accumulating seepage water.
• Use class (Nutzungsklasse) – how dry the room has to be. Class A: no water passing through in liquid form and no damp patches on the inside – the standard for living spaces and high-quality basements. Class B: limited damp patches are acceptable, for example in underground car parks or simple storage rooms.

If the basement is to become an office, hobby room or guest room later, watertight concrete alone is often not enough. Moisture can travel through the concrete as vapour and condense where insulation and ventilation are unfavourable. Building physics, insulation and ventilation then belong in the plan.

Cracks in concrete can never be ruled out completely. The WU guideline names three ways to deal with them:

1. Avoid through-cracks – through the concrete mix, reinforcement, joint layout and curing.
2. Limit crack widths – so narrow that the cracks close by self-healing: seeping water dissolves components from the cement paste that precipitate again as lime in the crack and block it.
3. Accept cracks and seal them as planned – for example by injection as soon as they appear. This has to be planned and agreed from the start.

The structural engineer decides which principle applies. For you as the client this means: a damp crack in the first months is not automatically a defect, but it should be documented and watched. If it keeps carrying water, have a specialist look at it.

• Geotechnical report with the design water level – without it the stress class cannot be set properly.
• Agree the use class in writing. If you want to live in the basement later, settle that before construction starts, even if it is only storage at first.
• Joints and penetrations: have them inspected before the pour. Later core drilling through the tank is a risk and needs suitable sealing systems.
• Collect documentation: delivery notes, photos of the installed waterstops and penetrations, curing records.
• Defects: report them promptly and in writing within the warranty period.

The Verbraucherzentrale gives the white tank a service life of 60 to 80 years. Joints, penetrations and cracks remain the typical weak points all the same. If groundwater gets in there, according to the GDV this is not an insured natural hazard – groundwater is only covered if it reaches the surface and enters the house from there.

A white tank in groundwater needs no drainage system, so there is often no pump sump either. In that case Drainbee has nothing to measure. It makes sense where the basement has a pump sump or a lifting station, for instance for floor drains or wastewater below the backflow level. Drainbee does not detect damp cracks in the wall.