A reinforced concrete raft is the most common and preferred type building foundation for structures where some or all of the structure is earth retained. In many cases the only joint, the main passageway for water leaks, is a compressed joint, in the horizontal, where the walls are built from the raft foundation.
Whilst well compacted and correctly reinforced concrete is waterproof, the joints between the concrete elements are not and it is possible that poor workmanship, poor design results in a concrete that is not as waterproof as intended.
If not waterproofed, the structure is at risk of allowing water ingress where cracks occur, at construction joints and through defects to the concrete itself.
Depending on the end use and habitable grade of the structure, the designer may have decided that two or even three forms of waterproofing are required.
Cracks within the concrete due to poor compaction or insufficient steel reinforcing. Water leaving the concrete during the curing stage leaves behind a complex capillary matrix through the whole concrete depth.
Cracks of 0.3mm and above are not deemed to be self healing and the inner concrete surfaces could suffer from slight moisture seepage. Moisture can move through the capillary structure to the inner surface of the structure.
Moisture to the inner raft surface that may not be acceptable for the required habitable grade.
The joint where the wall is supported from the raft and possibly at construction joints within the raft are weakness within the structure that could lead to water ingress.
Water seepage that could pressurise the internal finishes leading to severe impact on the internal habitable space.
Wall/raft or 'kicker' joint
Poor compaction of the kicker is a common reason for water ingress of concrete structures. The resulting honeycombing is not sufficiently dense to withstand water pressure.
Water seeps through the poorly compacted joint leading to severe impact on the internal habitable space.
Isolating the internal habitable space and fixtures and fittings from dampness and slight water leakage through slight concrete defects and slightly leaking joints between the concrete elements of the structure.
Newton System 500 is an internally applied Type C cavity membrane system that includes cuspated (studded) membranes to floor and walls and drainage channels sited at weaknesses within the structures such as below the kicker, at the wall raft junction for kickerless walls and above all joints to the raft. Water collected by the system is either removed by gravity to a point below the structural raft or to a pumping system.
Preventing water ingress of through raft construction joints
Newton 303 PolyProof Newton 303 PolyProof is a hydrophilic, thermo-plastic elastomer waterbar, which swells when activated by moisture. It is characterised by high elasticity and high tensile strength. Newton 303 PolyProof can be used to seal the structure against water leaks to both poured concrete and precast construction joints.
The swelling is achieved through special hydrophilic polymers, which are inseparably linked within the carrier
material (TPE). This ensures that high elasticity and exceptional tensile strength results even when fully expanded within the joint.
Preventing water ingress at the wall/raft construction joint.
Newton 312 BentoProof is a hydrophilic bentonite /rubber waterbar which swells when activated by moisture to seal the compressed joint of the concrete core with the concrete raft.
The internally applied Type C cavity drain membrane system, Newton System 500 can deal with significant volumes of water ingress but should be designed in conjunction with the waterbars as well as good concrete design and placement so that the Type C system is dealing only with the slight leakage that may come through the Type B integrally waterproof reinforced structure
With the joints fully and correctly waterproofed and with Newton System 500 correctly designed and installed, the structure is fully waterproofed to the following forms of waterproofing identified within BS8102:2009:
Type B plus Type C
and is suitable for habitable grades as defined by BS8102:2009:
1, 2 and 3.
A further form of waterproofing can be added to the design with the inclusion of Newton System HydroBond, an externally applied Type A membrane system. Please see Newton Specification Sheet A43-1, or with the inclusion of an internally applied Type A waterproofing system. Please see Specification Sheet A13-13 Internal Waterproofing of Basement with Concrete Raft and Concrete Walls
If the concrete contains severe honeycombing this poor concrete must be repaired. Please see Specification Sheet A1-11 Reapair of Honeycombing