An overview of Structural Waterproofing to BS 8102:2009

31st May 2013

Basement Waterproofing Waterproofing Classification

An overview of Structural Waterproofing.

In order to develop a robust waterproofing system for protecting a structure against ground water, BS8102:2009 has been set in place to give recommendations and to provide guidance on methods of dealing with, and preventing the entry of water from the surrounding ground.

Some points and considerations.

A. The Design Team

When designing a waterproofing system a Certificated Surveyor in Structural Waterproofing (CSSW) qualified specialist should be part of the design team.

This specialist should be:

          • suitably experienced
          • capable of devising solutions that can accommodate the various project constraints 
             and needs
          • provide the design team with information and guidance that assist with and influence 
            the design, installation and future maintenance of the waterproofing structure.

 
B. System Design
Here are a few points which should be considered when looking at a structure below ground:

          • During the life of the structure, some degree of ground water pressure is likely to
             build up against the structure / waterproofing system.
          • Cracking or defects in the waterproofing system can provide a potential path for 
            water ingress.
          • Even when the site indicates dry, the risk of some waterlogging in the future should 
             be assumed.
          • When inspecting an existing structure, where possible checks should be made to 
             determine the presence of existing waterproofing systems.
          • The potential of movement between the walls and the floor.
          • Groundwater and external drainage conditions.


 
C. Water Table Classification
Where water table classification is under taken, the water table should be considered to be in one of the following three categories:

High – This is where the water table is perched or is permanently above the underside
                  of the base slab.

Low – This is where the water table or a perched water table is permanently below the 
                 underside of the base slab. This only applies to free draining substrates

Variable – where the water table fluctuates.

 
Remember ground water will require time to drain away and can result in limited pressure periodically.


D. Reducing Risks in Waterproofing
 
 
          * Use combined protection
          * Incorporate appropriately designed sub surface drainage and ensure it is maintained
          * Use a fully bonded waterproofing barrier
          * Lower the permeability of the main structural walls
          * Use concrete with a waterproofing admixture, e.g. to BS EN 934
          * Ensure the discharge system, eg pumps, are maintained so that the system remains 
             effective.

          * Where appropriate, the site should be dewatered at least until such time as the below
             ground structure and waterproofing is completed


E. Types of Waterproofing
When making the selection for a waterproofing system considerations should be given to:

          • The need for a combined protection
          • Water table classification and required performance levels 
          • The need for continuity in protection

 
Type A (barrier) Protection, often referred to as ‘tanking’
This usually takes the form of:

          • Bonded sheet membranes
          • Lquid applied membranes
          • Bentonite clay
          • Mastic asphalt
          • Cementitious crystallization and multi-coat renders


When specifying barrier protection some essential points which should be considered are:

          • The nature and suitability of the structure and substrate, with the likelihood and the 
             effects of structural or minor movement or deterioration.
          • The ability of the barrier system to accommodate any minor movements
          • The feasibility of installing the waterproofing system, together with site conditions.
          • The need for an internal or external application
          • The effects of environmental contaminants.


 
Type B (structurally integral)
 
Type B protection should be constructed of reinforced concrete or structural steel and designed in accordance with the relevant part of BS EN 1992 or BS EN 1993 respectively.

When specifying this method, here are some of the factors that should be considered:

          • The design of the structure and the specification of the materials
          • Curing
          • Site conditions and suitability


 
Type C (Drained) protection
 
Manages the water that penetrates through the shell of the structure, by collecting it and directing it to a suitable drain off point.
To maximise the long term integrity and effectiveness of a Type C waterproofing system it should be designed to be maintainable, access points which allow routine maintenance of channel outlets should be incorporated.

In order to develop a robust Type C system, here are some of the factors which should be considered:

          • The likely highest level of the water table, the drainage characteristics of the soil and other
             specific properties, and the ability of the structure to hold back water
          • The intended use of the structure, with considerations given to any requirements for future
             flexibility


 
System Defects and Reparability
Ideally a waterproofing system should be defect free, however it should be noted that two types of defect might occur in any waterproofing, where a structure is subject to water pressure, and could mean that the internal environment in not met. The defects are as follows:

          a. Defects owing to defective workmanship or the inappropriate us of materials
          b. Defects owing to the specific properties of the material being used


It is essential that construction methods and materials used to realise the design are such that defects in a) are avoided. The defects in b) which are generally minor should be recognised and catered for in the design. Contingency planning for dealing with any localised defect or system failure that arise should be included in the overall water-resisting design of the structure. In either case, the issue of reparability should be taken into account and the feasibility of remedial measures assessed.
 
A risk assessment should be carried out which considers the long-term water pressure, effects of surface water infiltration and the use of external drainage and cut-off walls.
          a. The effects of climate change, burst water mains and sewers, adjacent trees, sulphates,
               radon, methane and other gasses and contaminates
          b. Where external drainage is proposed, the effects of drawdown on adjacent structures, 
               the potential of silting of drainage and biofouling issues



Water proofing measures should be designed on the bases of water to the full height of the retained ground at some time during the structures life where:
          a. No detailed geological or hydrogeological assessment has been undertaken.
          b. The result of the soil investigation are inconclusive with respect to groundwater
          c. The ground characteristics are un-reliable
          d. The drainage measures either internal or external are unreliable or un-maintainable and
               infiltration cannot be controlled



Protection against water ingress from the following three sources should be considered:
          1. The inflow of surface water, ranging from peculation of rain to the inundation of water
               from burst water mains.
          2. The water acting on the external retaining wall system
          3. Water pressure below the slab

 
The water resisting design should enable the system to withstand a predetermined head of water or control the water before it reaches the structure. Where practicable, provisions should be made to prevent or reduce percolation of rainwater into the ground such as collecting and disposing of surface water and the installation of sub-surface drainage i.e. permeable granular fill or under slab drainage etc. The risks of not carrying out planned maintenance with type c protection e.g. blocked drainage, pump failure.


The designer should discuss the following points with the client prior to deciding on which type (s) of waterproofing protection to use:

          * Initial capital cost compared with costs for future maintenance and any necessary
             upgrades
          * The scope of the testing during installation
          * The risks associated with aggressive groundwater and other ground contaminants, 
             which may require the use of specific protection barrier.
          * The need or ability to provide heating or ventilation and the consequences arising in
              terms of water vapour

The insertion of a ground barrier for the prevention of radon, methane and other gasses and contaminates from entering the structure should be discussed and considered in the design, as should the choice of the materials, insulation and installation methods of any waterproofing system.


Other Remedial Waterproofing Methods
Isolated remedial measures are often required and the following methods could be used:

          • Pressure or vacuum grouting including cementitious, Bentonite, polyurethane, resin and
             rubber latex products.

          • Resins or cementitious coatings

          • Injection waterproofing using flexible Gels and flexible / rigid resins.
 
For the majority of these solutions specialist equipment and knowledge is required.



For expert advice from CSSW qualified surveyors please give us a call…………….

Filed under: Surveying, Waterproofing,

Tagged as: Basement Waterproofing to BS8102, Type A Waterproofing, Type B Waterproofing, Type C waterproofing,

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