Basement or any below ground structure that is formed by base slab, walls and top slab, is partially or fully exposed to the surrounding soil and groundwater, resulting in specific exposure and stress from the prevailing permanent or temporary environmental conditions. The impotance of waterproofing is vital, as water ingress will result in physical attack and deterioration of the concrete structure. Selecting, designing and installing the appropriate waterproofing system for basement is critical, as even small mistake can lead to significant problems and costs down the line.
Concept and Strategy
Integral Waterproofing System
The waterproofing system is integrated into the concrete structure. Water penetration is stopped by the structure itself and cannot entirely pass through the basement. Typical products are admixtures for watertight concrete combined with appropriate joint sealing systems for connection, construction and expansion joints.
External Waterproofing System
The waterproofing barrier is applied on the external surfaces that are exposed to ground water (positive side). The structure is protected against water ingress and also against any aggressive substances or influences. Some materials, such as post applied waterproofing mortars and coatings, access to the external surfaces is required for application after concreting.
Internal Waterproofing System
The waterproof barrier is applied on the internal surfaces of the structure (negative side). These systems do not prevent damage to the structure from water ingress, nor concrete damage due to aggressive chemicals. Generally these systems are applied as coatings or sheet membrane linings, and is only recommended for refurbishment works in example where access to the directly exposed surfaces is not possible.
Waterproof Mortars and Bituminous Coating
Sika waterproof mortars and bitumen based coatings are rigid or semi-flexible waterproofing products. They are supplied as ready to use solutions for many basements to seal against damp soil, seepage and percolating water. They must be pre-applied on suitable substrates under new structural concrete slabs and are generally postapplied externally on new walls. They must be used in combination with appropriate joint waterproofing systems for the connection, construction and movement joints. Good external drainage with a permanent dewatering system is also necessary; normally using drainage pipes placed at or below the level of the base slabs to prevent any build-up of water pressure.
Watertight Concrete System
The “Sika White Box Concept” involves optimum structural design and reinforcement together with an integral rigid waterproofing solution. This consists of a waterproof concrete combined with appropriate joint sealing systems for any necessary construction and movement joints. To produce concrete that is impermeable to water, special admixtures including superplasticizers and pore-blocking or crystalline agents have to be used, in order to also ensure optimum consistence, flow and ease of compaction in a dense matrix with minimal voids. For sealing the joints, many different Sika solutions can be used including hydrophilic sealants / profiles, waterbars in various material qualities, injection hoses or sealing tapes, dependent on the type and location of the joint and its requirements.
Wet Bonded Waterproofing Membrane
SikaShield® W is a sheet membrane waterproofing system consisting of a cross laminated HDPE carrier film laminated with a modified bitumen based adhesive on both surfaces. Due to the double-sided structure the SikaShield® W system can be installed single or (partially) double layered and does not require any accessories such as tapes and pastes etc. The membrane can be both pre-applied under the slab as well as post-applied to the walls by the use of a one-component bonding mortar.