Tanking and Waterproofing
Tanking a cellar, basement or other underground earth retaining structure? You have heard of the term 'Tanking'. What does it mean?
Image 1. Water pressure coming to bear on a structure can induce bending stresses which the structure may not be designed to withstand. Floor slab has broken as a result of this.
'Tanking' is a generic term used to describe a method of waterproofing where a pressure resistant barrier is installed to either the inner or outer face of the structure, with the intention that the barrier with withstand water pressure as it comes to bear, and thus prevent any water leakage.
An underground structure that has been tanked will most likely fail if subjected to external water pressures. The reasons for this are many, but the two most likely reasons for ineffective tanking are the fact that the system needs to be 100% defect free in order to be successful, and that is just not reasonable; and secondly, when water is resisted by the tanking, the water pressure increases which leads to greater bending stresses within the structure, which in turn leads to failure of the tanking.
Image 2. Failed cementitious tanking system. Cause: inability of the cementitious
It is vitally important to get the appropriate waterproofing solution correct first time!
BS8102 : 1990 is the British Standard for the waterproofing of structures below the ground. All those designing a new earth retaining structure or indeed upgrading an existing structure, should be aware of the requirements of BS8102. The whole document is some 38 pages long, and we are therefore unable to represent the document in full. However, we have included some pertinent paragraphs:
"Almost all basement structures are likely to be subjected to water pressure at some period of their life."
"For basements not exceeding 4m deep, a design head of ground water, three-quarters the full depth below ground is adequate".
Image 3. Failed basement waterproofing. Cause: Main Contractor attempted to save money by using roofing felt!
In layman's terms BS8102 is saying that we should always expect water ingress at some point and that we should expect the water surrounding the basement to be at least ¾ the depth of the basement. This is very important as it confirms that one should always waterproof any structure that is earth retaining.
A waterproofing designer has to consider environmental grades (what the space is to be used for ) as the first stage of the process using the grading system within BS8102. Once the environmental grade has been decided then a category of structure needs to be established. BS8102:1990 defines categories of structure as:
Type A: (Tanked protection) - The structure has no resistance to water ingress and so requires a continuous barrier applied to the structure.
Type B: (Structurally integral protection) - The structure itself offers the required protection to the required grade.
Type C: (Drained protection) - Water ingress is controlled and channelled away from the structure via cavities formed within the walls and floor.
Newton waterproofing systems are categorised as Type C: as unlike with tanking membranes, our systems do not attempt to blindly hold back the rising water pressures. By forming pockets of air-space, our systems allow for the water to depressurise within these air-spaces to be simply removed from the structure using either safe gravity drainage or a sump pump system. BS8102 states that: “For those seeking maximum assurance this combination of construction and waterproofing (Type C) is considered the most effective and trouble free.
Newton's Waterproofing Solution:
Newton System 500 is categorised as Type C. (drained protection) and will offer the highest level of protection from water ingress to your underground living space.
The range of Cavity Drain Membranes within Newton System 500 allow for water ingress to be controlled, drained and discharged from the structure. When Newton System 500 is fitted to the walls and floor of the structure, the membranes create a dry and habitable inner environment, whilst the waterproofing carries on unnoticed behind the system.
Newton System 500 is quick and clean to install with no heating, mixing or torching required and very little substrate preparation. As well as having superior waterproofing qualities Newton System 500 is much quicker to install than tanking products such as asphalt, dense renders and paint on or sheet bitumastic systems. In many cases, Newton System 500 can be installed in the time it takes to prepare the substrate for tanking due to the latter requiring damaging processes such as grit blasting and scabbling to enable the tanking to 'stick'.
More details of our waterproofing systems can be found in our product brochures. Please Contact our office or see the Request Brochure link on the home page.
Image 4: Newbuild waterproofing with Newton System 500 – clean and cost effective.
Our pre-sales Technical Advisers will be glad to be of service and will help advise you on your project.
Contact our office to locate the John Newton & Co Ltd registered installers near you.
