Combination waterproofing systems can offer optimal structural protection against water ingress.
BS8102:2009 offers guidance on 3 types of Below Ground Level Waterproofing Systems used in the United Kingdom. These are categorised as Types: A, B & C.
Type A is defined as ‘barrier protection’. A material is used to offer a barrier to the passage of water. A barrier protection which physically holds water back on either the positive side of a below ground level structure (externally), the negative sides (internally) or sandwiched into the construction. Cementitious coatings, bituminous coatings or flexible sheet membranes are categorised within Type A ‘barrier protection’.
Type B is defined as ‘structurally integral protection’ and the structure itself is constructed as an integral water resistant shell. A concrete structure is built which includes watertight concrete admixtures, hydrophilic strips/water bars (passive or active). When considering and/or specifying a Type B integral system, a clear knowledge of concrete construction is required to meet BS8102:2009 specifications. A robust strategy is to design the concrete in accordance with BSEN:1992 Euro code 3.
Type C is defined as “drained protection” and functions by diverting a passage of water away from the structure (which is usually collected into a submersible pump). A drained cavity system collects and manages any moisture which breaches the integrity of the structure by channelling, collecting and discharging such free water via a suitable evacuation point. A Type C waterproofing system will not increase or exert water pressure on a structure nor alter the dynamics of a structure.
Combined Waterproofing Systems
Some designers and Structural Warranty Providers specify that 2 forms of waterproofing are used in conjunction when Waterproofing Basements and Below Ground Structures. These specifications will require a “combination” of Types A, B & C waterproofing systems to achieve waterproofing performance and to meet BS8102:2009 criteria. It is always prudent to source these systems if possible from a single source/supplier, as this factor will dramatically reduce risks associated with compatibility of products and also greatly assist with technical design issues.
The NHBC 2016 technical manual ‘Chapter 5.4’ states that a “dual system” (two waterproofing systems) must be incorporated to structures where a Structural Warranty is provided.
Combination systems can be used for convoluted/difficult shapes to waterproof. A liquid/cementitious (Type A) system can be lapped behind a Type C system, to provide continuity of the waterproofing design.
Combined waterproofing systems are an effective solution when waterproofing car parks/podium decks and buried roofs and can be beneficial where continuity is difficult for example when encountering tight boundaries.
Delta's Koster product range is suitable for Type A waterproofing and offers solutions to repair of Type B structures through crack injection to water stopping also to include curtain wall injection. Koster products work in harmony with Delta’s Type C Cavity Drain Systems and ensure a robust and watertight solution.