An Introduction to Waterproofing

Having recently embarked on training for the Certified Surveyor of Structural Waterproofing course (CSSW), to join my many colleagues who hold this certification, one of the first Modules I completed was focused on an Introduction to Waterproofing. To solidify my knowledge, I wanted to write this article for my own benefit but for others connected with the industry to gain new insights. So, what were some learnings?

Roles and Responsibilities in Waterproofing

We learned about collaborative roles of designers, warranty providers, manufacturers, and installers. Each plays a pivotal role in ensuring effective waterproofing solutions, from conceptual design to installation and maintenance. The main question to ask in the early stages is 'Who is taking the design responsibility for the Waterproofing? Who does the design liability sit with?'

Reflecting on this point, I find this can often be a grey area in the construction industry, with the architect and structural engineer understandably not wishing to take responsibility for waterproofing design. This is where a specialist waterproofing manufacturer such as Premcrete can be engaged to work with the design team at an early stage in a detailed design capacity, taking full design liability for this specialist element.

The Imperative of Waterproofing

As obvious as it may sound, Waterproofing is absolutely essential in safeguarding structures below ground, such as basements, tunnels, pools and resevoirs. Waterproofing prevents water ingress, which can cause structural damage, health issues and significant disruption and loss to buildings which are in use, if not designed and installed correctly. Understanding the science behind water penetration and control is vital for any construction professional.

Industry Bodies

Resources relating to structural waterproofing can be found at these industry bodies;

• Property Care Association (PCA) https://www.property-care.org/home
• The Basement Information Centre https://www.basements.org.uk/
• British Strutural Waterproofing Asscoiation (BSWA) https://www.thebswa.plus.com/
• MPA - The Concrete Centre https://www.concretecentre.com/

It should be noted that the CSSW trianing we undertake at Premcrete, is done through the Property Care Asscociation in the UK.

Guiding Documents and Standards

The following standards are the most central to the recognised guidance for Waterproofing. These documents guide the design and implementation of waterproofing systems, ensuring they meet the required efficacy and durability.

• BS8102:2022 Protection of below ground structures against water ingress -This is likely to be the most common UK Code of Practice used by Waterproofing designers and installers, and has been recently updated from the previous 2009 edition.
• CIRIA 139 & 140 - These are publications from the Construction Industry Research and Information Association (CIRIA) related to waterproofing and construction.
• PCA Code of Practice for Remedial Waterproofing of Structures Below Ground - There are many codes of practice provided by the Property Care association, however this is the most specific to below ground waterproofing.
• BS8110 (BS EN 1992- 1&2) - Code of Practice for reinforced Concrete
• BS8007 (BS EN 1992- 3) - Code of Practice for Design of structures retaining Aqueous Liquids
• BCA/BSWA - Basement waterproofing design Guide
• Guidance Document - Basements for dwellings
• The Building Regulations
• Warantee Providers

A Certified Surveyor of Structural Waterproofing needs to be familiar with all of these standards, as when considered together they inform the final design or report findings & reccomendations.

Materials commonly used in structures requiring waterproofing

There are various materials used in constructing Below ground structures, and how and where water ingress can take place.

Materials include:

• Concrete or Reinforced Concrete
• Concrete Blocks
• Bricks
• Mortar & Screed

This segment highlights the importance of selecting the appropriate materials according to the Waterproofing Risk, and being aware of where leaks can take place (see diagram below). This serves to deploy the correct construction techniques for effective waterproofing, and managing water ingress.

Basements can be constructed in various different ways but here are some of the most common;

• Piled Walls with or without a poured concrete liner wall
• Poured concrete wall
• Masonary or Blockwork wall construction
• Precast panel system.

There are many ways to construct a basement and whilst cost can be factor, safety should come first, both from a structural compliance perspective and also based upon the Water Table/Water ingress risk.

Permeability of Water & Vapour

Permeability of Water through materials depends on 3 main factors;

• The Head of Water
• Capillary size
• Capillary length

Permeability of Vapour through materials depends on the following factors;

• Vapour pressure difference on either side of the material
• Capillary size
• Capillary length

It must be recognised that whether the water permeates as a liquid or a vapour, they both amount to Water ingress, and knowing these factors helps us to design the appropriate waterproofing systems.

Properties of Water - Hydrogen Bonding

Hydrogen Bonding is a property of water, which in simple terms, makes water sticky! The hydrogen bonds between water molecules are responsible for the cohesion of water, which is the force that helps to keep water molecules together. When air and water meet surface tension is created. In other words Water never sleeps!

So how does this relate to Waterproofing? This 'property of water' (Hydrogen Bonding) enables some materials and structures to be vapour permeable but not significantly water permeable. Examples of these materials include waterproof cementitous slurries ie; Hydroseal FX and renders ie; Hydrorend. Whilst they are formulated to resist Hydrostatic Pressure, they are always vapour permeable.

The difference? Hydrostatic pressure exerted of any incompressible fluid in a confined space ie; Water, purely in a liquid form, as opposed to Vapour pressure (Atmospheric Pressure) which is a compressible fluid in the form of air which contains liquid.

If the above mentioned waterproofing coatings (usually applied on the inside of a structure) were not vapour permeable. This can lead to condensation, and increased Hydrostatic pressure within the building structure/fabric. By reducing the Hydrostatic pressure we are reducing the likelihood of water ingress.

What is 'Dry'?

In reality, there is no such thing as a perfectly dry space, as some level of moisture is always present. Therefore it is something that is percieved as dry, when the moisture present does not adversely affect the occupants, plant and materials in any particular environment.

This is where Relative Humidity (RH) comes in! This is expressed as a percentage, and measures water vapor, but RELATIVE to the temperature of the air. In other words, it is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature.

Therefore if we have an office environment with a 20% air temperature, and the RH is 60% this would be perceived as dry, however the same perception may alter if the environment was paper archive store, and may be considered slightly damp.

This then begs the question what are the ways we can produce a dry basement? There are two distinctive ways to acheive this;

• Reduce Water Penetration to an acceptable level or stop it altogether
• Reduce Relative Humidity to an acceptable level by Ventilation, Airconditioning, dehumidification or other appropriate means.

What are the 3 Types of Waterproofing?

So how do we keep water out? There are 3 main Types of Waterproofing; Type A Barrier Protection, Type B (Integral or Built Protection), and Type C (Water Management), and via other Drainage methods outside of the structure.

Type A Barrier Protection;

• Pre-Applied Bonded Sheet Membranes. These often incorporate a fleece or woven texture backed membrane to encourage the bonding of the membrane to the surface of the concrete. Some preapplied membranes include Combined Self healing & Fully bonded technology ie; Maxiprufe Plus or Combiseal. The bonding nature resists lateral movement and migration or tracking of the water, and therefore localising any defect which may occur.
• Post Applied Bonded or Self Adhesive membranes. These can be heat bonded, but are more commonly availible as a cold applied product, and self adhering, such as Hydroprufe 3000
• Bentonite Membranes - This is a somewhat traditional form of waterproofing and Premcrete, as a manufacturer, have decided to exclude this product from their range, and replaced it with a more advanced combined self healing and fully bonded membranes as cited above
• Liquid Applied Membranes ie: Epoflex MMA , Hydroguard PUA or Hydroprufe LG. These vary from Hand applied (brush or roller) self install products, to specialist hot and cold spray applied applications.
• Cementitious Slurry Membranes ie: Hydroseal FX or Hydrorend
• Cementitious crystallisation powders/slurries ie; Hydroseal PX
• Loose Laid Membranes and DPMs such as Hydroprufe DPM. When incorprated within a wider waterproofing design, Premcrete can extend the warranty to cover the whole substructure protection.

Type B Integral Protection;

• Water resistant concrete admixture or additive ie Hydrocrete, and ancillary water bars such as Hydrostop BR and Cemflex VB
• Concrete designed to less than 0.2mm crack width which as waterproof concrete in its own right, but typically won't come with a warranty from a supplier or manufacturer.
• Crack Induced concrete
• Sheet steel piles with welded clutches are recognised as a form of waterproofing, but aren't typically included in a warranty from a waterproofing supplier/manufacturer.

Type C Water Management & Other Drainage methods;

There are two ways of introducing drainage.

The First, is to drain and manage the internal ingress of water into the structure, commonly known as Type C Waterproofing, with the use of the following;

• Cavity Drainage membrane systems, including perimeter Drainage channels, and Sump Pumps ie: Hydroflow HP

The Second is where external water needs to be removed, either temporarily or permanently. These include;

• Site drains (To remove surface water during construction)
• Site dewatering (To remove Groundwater during construction)
• Land Drains to permanently remove occasional groundwater.
• Surface drains and surface drainage membranes ie: Hydroflow HM to permanently remove surface water

Thats it for the waterproofing introduction! As you can tell there are alot of elements to be aware of you will be glad to know its the role of a CSSW qualified waterproofing designer to navigate the various standards and guidelines, to produce a compliant design, and assume design liability.

We look forward to sharing more insights and going into greater detail in further articles, and playing our part in contributing to and educating the industry as to Waterproofing best practice.

Meanwhile if you have any questions or feedback, or if you would like to discuss an upcoming project, please reach out to me via email [email protected] or be free to visit our website www.premcrete.com