Structural Waterproofing Solutions in Line with BS8102
25 November 2019
Posted by: Steve Cushion, Eastern Regional Committee Member
The November CPD Event at the Norwich Centre of Excellence was presented by Alan Sleigh, Commercial Manager of Triton Systems on the subject of Waterproofing of Below Ground Structures.
Alan first introduced the company, which is now 40 years old and started in timber and damp treatment. This area is now in decline and therefore company has migrated into waterproofing and ground gas control measures. The company now offers:
- Technical support - including BIM and NBS
- INK - PI design
- New Build waterproofing
BS 8102:2009 was then discussed in detail including Grades of Waterproofing, System Types and Site Practice.
- Grade 1 - basic utility where some seepage and damp patches can be tolerated.
- Grade 2 - better utility where no water penetration can be tolerated, but internal atmospheric vapour is allowed.
- Grade 3 - habitable which requires a dry environment.
The system types were reviewed:
- Type A - tanked membrane
- Type B - integral, usually with admixtures
- Type C - drained cavity
Health and safety considerations of the application of the various materials were then discussed.
Alan then turned to Table 1 of the Standard and the assessment of the protection requirements and the effect of the presence of a water table. Certifying insurers such as NHBC can require a combination of two of the Types.
The system Types were then discussed in detail.
Type A forms an external barrier and can consist of pre or post applied renders, liquids or sheets.
Type B modifies the structural concrete in the form of crystalline waterproofing admixtures which can lay dormant until water starts to enter the structure which causes the admixtures to react with the free lime in the concrete to form insoluble salts which block fissures and capillaries and stops the further passage of the water. Crack width control is important and reinforcement must be designed to limit crack width to 0.3mm (0.2mm in the case of water retaining structures)
Type C utilises a drained cavity and water management system including sumps and pumps. This Type must be used where there is external hydrostatic pressure. Whilst it is one of the most reliable of the methods it does require maintenance of the associated services.
The various combinations of the two Types to meet insurer's requirements were then discussed followed by a review of typical good detailing and site practice including provision of fillets to avoid sharp corners and construction of land drains to minimise external water flows. The specification of water bars was covered together with the benefits of achieving sustainable waterproof concrete.
Alan concluded his presentation by covering a typical Type C installation in detail including the provision of duplicate pumps with battery backup in case of mains power failure.
Eastern Regional Committee Member