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Type B Waterproofing

Type B protection as defined by BS8102:2022 (Code of practice for protection of below ground structures against water ingress) is where the structure itself is constructed as an integral water resistant shell. Invariably built of reinforced concrete, the basement structure must be designed within certain strict parameters to ensure it is water resistant. Given that concrete is normally part of the make up of modern basement structures it is logical to try and incorporate a waterproof element to prevent ground water ingress.

The water tightness of the Type B construction is reliant upon good design and construction. Using a concrete of low permeability, and appropriate joint detailing although defects can be minimised by correct specification and design and by careful construction.  

PCA - Type B Waterproofing

When Type B might be used 

Due to the integral nature of Type B waterproofing it is typically used in new construction. An appropriately designed waterproof concrete structure is acceptable in all types of water table.

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Why Concrete is often used for Type B protection

Economic viability and availability mean concrete is the most common material used in modern basement & below ground construction. There are a variety of methods in which concrete is used including;

  • In-situ concrete
  • Insulating Concrete Formwork (ICF)
  • Precast concrete
  • Twin Wall

Concrete by its very nature is water resistant, but there are essential two methods of making it waterproof. The first is the use of steel reinforcement bars to control cracking to a point that any cracking will not allow the passage of water.

The second is the use of admixtures, which “act to reverse the capillary or ‘sucking’’ action of the tiny capillaries on the concrete surface and to effectively block the pores within the concrete when subjected to hydrostatic pressure.”

DOWNLOAD - Best Practice Guidance: Type B Waterproofing Systems

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Important to consider Construction joints with Type B

Construction Joints need particular attention when considering and installing type B waterproofing as these are the area’s most commonly associated with leaks. 
Joints between components, movement joints and day work joints should be durable, watertight and include appropriate water stops or hydrophilic protection. Kickers, usually cast as part of the slab should also be “watertight concrete” and are used to form the joint with the walls.

The construction of a ‘kicker’ after pouring the floor slab should not be encouraged as it is difficult to construct without defects. Therefore kickers should be cast with the slab using appropriate edge formwork, but will require careful construction to obtain full compaction. Modern types of formwork and kicker less construction techniques mean that kickers no longer need be part of the construction process. 

Water stop & Type B protection

Water stops should be used to provide enhanced resistance to water transmission at construction joints in the concrete structure, e.g. at construction or day work joints, services or other penetrations. The principal types of water stops can be classified as the following:

+ 1. Passive sections:

These are rubber or flexible polyvinyl chloride (PVC) extruded profiles cast into the concrete on both sides of the construction joint, either at the concrete surface or mid-depth of the concrete section, to form a physical obstruction to water transmission.

+ 2. Active or hydrophilic strips or crystallization slurries: 

Preformed profiles or sealant composition of materials applied to the concrete joint at depth in the section.
Permeable hose or other sections that are fixed to the construction joint surface before casting the second pour, to facilitate the injection of a specialist sealing resin into the joint, when required.

+ 3. Permeable hose or other sections:

With permeable hoses or other sections that are fixed to the construction joint surface before casting the second pour, to facilitate the injection of a specialist sealing resin into the joint, when required.

Consideration of the Water table

With a high water table, minor defects in the concrete usually result in only small amounts of water penetrating, and stopping these is usually fairly straightforward. Remedial action may, depending on the form of construction, be carried out from the inside, so avoiding the need for external excavation.  

Variable water tables present a reduced problem, unless the water table stays high for a long time. In a free-draining site, it is rare for a defect to be so serious that the water comes through by capillary action. The water and water vapour resistance of Type B protection relies on the materials incorporated into the external shell of the structure itself and will be a function of the section thickness. Defects are not always identified during construction stage and only become evident after completion.

How Type B Waterproofing systems can fail

One of the most regular causations of failed waterproofing systems is defects in the installation. Typically type B waterproofing systems will usually require that they are installed under license of the supplier/manufacturer. However, in practice this does not always happen and it is not uncommon for waterproofing systems to be installed by operatives who have no relevant qualifications and/or no previous experience of installing waterproofing systems. 

This should not happen and it is the responsibility of the main contractor and installers to ensure the installation is undertaken by suitably trained operatives.

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Failed type B waterproofing - Property Care Association

Types of defects common with Type B waterproofing

The most common defects are: 

  • Permeable concrete
  • Honeycombing through lack of compaction
  • Contamination of or cold joints
  • Cracks due to thermal contraction and shrinkage
  • Poor and inadequate placement of waterbars, hydrophilic strips and joints

+ Lack of Compaction - The most common defect:

The most common defect is “honeycombing / lack of compaction. The main cause is the wrong choice of consistence. Either the consistence was too low making compaction difficult or the concrete had extra water added and segregation took place.

+ Cracking:

Plastic and long-term drying shrinkage, thermal cracks, induced cracks, cracks caused by restraint are normally associated with Designer and / or Contractor issues and NOT the materials used.

+ Thermal Cracks:

These are caused by temperature differentials, particularly in mass concrete due to the heat of hydration. As the interior concrete increases in temperature and expands, the surface may be cooler and contracting thus causing tensile stresses that may result in thermal cracks at the surface.

+ Drying Shrinkage Cracks:

As most concrete mixes contain more water than actually required for the hydration process, the remaining water evaporates over time causing the concrete to shrink. Restraint to shrinkage causes tensile stresses to develop in the hardened concrete. Restraint to drying shrinkage cracking is a common cause of cracking in concrete.

+ Plastic Shrinkage Cracks:

These are caused by the evaporation of water from the surface of freshly placed concrete faster than it is replaced by bleed water, thus causing the surface to shrink. Due to restraint from the underlying concrete, tensile stresses develop in the weak plastic surface concrete resulting in shallow cracks of varying widths and depths.

Type A Waterproofing

Historically known as “Tanking”, type A waterproofing provides protection (a barrier) against groundwater ingress by applying a waterproof material (such as cement) to the internal or external walls and floor slab of a basement or underground structure forming a barrier between the structure and any groundwater present.

More about Type A Waterproofing >> 

Type C Waterproofing

Type C protection has become the most common form of waterproofing system used in retrofit, existing basements and within new build basements. It allows moisture or running water to penetrate through the external wall or floor of the structure and to travel behind a cavity wall membrane to a drainage system and sump pump/pumping station.

More about Type C Waterproofing >>

Additional technical documents you can view

For those interested, there is a variety of structural waterproofing related 'Codes of Practice', Technical Documents, Guidance Notes via our Technical Document Library.  Simply click on the button below to view the library.  Documents of interest include:

  • Code of Practice for Waterproofing of Existing Below Ground Structures
  • Insulation in Basements guidance note
  • Best Practice Guidance: Continuity of Waterproofing Systems
  • Best Practice Guidance: Podium Decks and Buried Roofs

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Training courses that might be of interest

Want to learn more about structural waterproofing

For those interested in learning more about structural waterproofing and BS8102 requirements; there is a variety of PCA training options for surveying professionals as well as technical/trade professionals. 

Use the search tool below to find available waterproofing related training courses or simply go to our training & qualifications section.  Alternatively, if you want to chat to someone, contract our training team on 01480 400 000 or contact them online.

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Waterproofing design

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Types of Waterproofing - A,B & C

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