Steve Armfield, Product Development Manager for Sika UK

Specifiers are confronted with a dilemma of which of the two main options – hydrophobic or crystalline ­­– to choose when providing watertight concrete for below ground structures. As Steve Armfield, Product Development Manager for Sika UK, explains, a complete systems approach including sealing can offer the best of all worlds.  

What does the British Standard Say?

British Standard BS 8102:2009 gives recommendations and guidance to designers on how to deal with and prevent the entry of water in both precast and in situ structures, and describes four grades of waterproofing from some seepage being tolerated in Grade 1 to a totally dry environment in Grades 3. The standard also outlines three main types of waterproofing; Type A – a barrier applied to the structure internally or externally, Type B – a waterproofing system integrated into the concrete structure and Type C – a cavity drainage/water management system.


BS8102:2009 also suggests that consideration be given to combining systems (for example using Type A & B, Type A & C or Type B & C together) to provide further protection for the structure. Recently, the construction industry has been trending towards a dual protection approach when keeping water in a structure or protecting the structure from water ingress.

Type B Waterproofing

In this blog we are focusing on Type B construction, which relies on watertight concrete to provide the protection required. This is simply a concrete with high water penetration resistance, low water conductivity and a dense microstructure, produced with an optimised mix design that is improved using a choice of waterproofing admixtures.


Choosing one which will be most effective for their project can present a confusing challenge for specifiers. It is more likely that a complete system approach including all the options available will be the best way to achieve a fully watertight structure.

Watertight Concrete Technologies

The options available for watertight concrete admixtures break down into two main categories - crystalline or hydrophilic pore blocking. Although both ultimately achieve the end goal of blocking capillary pores within the concrete matrix to prevent water passing through a structure, they both realise it in different ways.

Hydrophobic Pore Blocking

The hydrophobic pore blocking technology method blends a watertight concrete powder with a liquid admixture to develop a polymer barrier inside pores during the hydration process. At the molecular level a hydrophobic pore blocker consists of long chain fatty acids such as stearates and oleates which chemically react when in the presence of calcium hydroxide in the fresh concrete. As well as repelling water the hydrophobic layer performs well when water exposure is inconsistent.

Crystalline Technology

Alternatively crystalline technology comprises a non-soluble crystalline structure formation in the capillaries. This results from chemicals reacting in the presence of calcium hydroxide CaOH (and other hydration by-products) and moisture, the structure filling and blocking the capillary structure, as well as small voids and micro cracks.


Although a lack of moisture will stop the reaction occurring, it will be reactivated when wetted, and offers high performance in consistent water exposure conditions. The formation of non-soluble crystalline structures also enhances concrete’s abilities to self-heal cracks, further reducing the concrete’s permeability and providing a fully watertight concrete structure.

The high-tech, Library of Birmingham building, which on completion was the largest public building in Europe, used Sika Watertight Concrete to prevent water penetration

Sealing Structures

Under BS8102:2009 guidance for Type B construction consideration is made to the concrete mix design and the practicalities of placing and compacting the concrete. Consideration also needs to be made to products and methods for sealing the structure. Using crystalline or hydrophobic technology will ensure a watertight concrete, however to create a fully watertight structure soft PVC waterbar seals should be used to protect all joints and penetrations.


For more information on Sika’s waterproofing solutions please visit