Tanking Walls

What is Basement Tanking?

Tanking is a term that refers to damp proofing walls by creating a complete water-impermeable barrier covering the entire wall. It is usually employed as a remedial method in situations where there is no access to the external wall of the structure, such as in basements and cellars.

There are two basic tanking systems: external and internal.

External tanking takes place while the building is being built and its main role is to protect the junctions where walls and floor meet. There are a lot of external tanking designs;however, the basic premise remains the same, as most of them are based on the use of a waterproof membrane that embraces the area that the cement is about to be poured. When it eventually dries, it is safely “tanked” inside, protected by humidity issues.

Internal systems are applied after the construction is completed, therefore they are considered as a remedial measure. As in external tanking, there are several methods of doing that. At Damp Proofing London, we use two main designs: DPM and Cementitious Tanking

DPM Tanking

The first is by applying a damp proof membrane (DPM) to the interior wall. This method in itself can be split into two types. The first of these consists of fixing sheets of polypropylene membrane to the wall with special membrane clips. The separate sheets are bonded with tape to create a complete seal and the membrane is then plastered over.


A DPM for tanking walls may also come in liquid form as a two-part epoxy-based membrane. This is applied directly to the underlying brickwork or masonry in two coats. The resulting waterproofed surface may then be rendered, plastered or painted directly.

Cementitious Tanking

The second main type of tanking is referred to as Cementitious Tanking. Cementitious just means that something is like, or pertains to, cement. With cementitious tanking, the wall of the structure is stripped back to the base material and then re-rendered with several coats of a sand/cement, mixed with special damp proofing products.

Cementitious tanking is normally used where the likely ingress of water is considered to be less than something that would require the fitting of a DPM. The advantage of a cementitious tanking system is that it is also vapourpermeable. As the movement of water vapour is generally outwards from the basement or cellar this allows the room to breathe.


Cementitious tanking systems normally require a period of curing for around a month before it is possible to decorate over them. It is important to note that any decorative coverings applied over the top of cementitious tanking must also be vapour permeable. This prevents a build up of humidity within the plaster (known as interstitialcondensation), which can cause damage such as blistering and peeling to the decorative covering. As a rule of thumb, it is generally considered that glossy, oil based paints are not suitable whilst water based emulsions are.

Our Step-by-Step Basement Tanking Guide

Step 1 - In most cases, the masonry is deemed too defective to repair and is totally removed, taken back to expose the original brickwork.


Step 2 - Once this has been completed the mortar joints are cleaned out and brickwork is washed to prevent salts contamination.


Step 3 - A waterproof mixture of 3-1 sand and cement is applied to a minimum of 10mm to the thoroughly prepared brickwork.


Step 4 - When the applied render is still green (not completely dry) a cementitious tanking solution is then applied to a minimum of 3mm again when the tanking is still green a further waterproofed 3-1 sand and cement render coat is applied to a minimum of 10mm.

cementitious tanking solution application

Step 5 - This can be left as is, painted or finish plastered depending on client’s instructions.


Damp Proofing London are fully affiliated and guaranteed by Triton Chemicals the country’s leading manufacturer in all waterproofing basement and cellar tanking products.

If you have damp problems in a cellar or basement, or considering a basement conversion and are concerned about possible damp proofing issues, contact a damp proofing specialist like us here at London Damp Proofing who will be able to advise you on which, if any, tanking system is suitable for your circumstances.


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020 8378 0089

Unit 142 Culvert Court, Culvert Road, London, SW11 5AU