Tanking is a term that refers to damp proofing walls retrospectively by creating a complete water-impermeable barrier covering the entire wall.
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.
The application of water proof materials to a wall forming part of a structure not entirely below ground to all walls can render the below ground area habitable with the least risk as long as water is diverted away elsewhere within the structure and safely away from the building.
Where a basement is totally submerged the aim is effective waterproofing of all walls
Assessment of Problem
Should be related to defective existing masonry salt and sulphate presence within the soil strata water table and pressure.
Ventilation and risk of moisture build up into water within the structure should be evaluated.
Types of Tanking
Methods of tanking can be divided into two main types:
The first is by an application of a damp proof membrane (DPM) to the interior wall.
The second main type of tanking is referred to as Cementitious Tanking.
Damp Proof Membrane (DPM)
This method in itself can be split into two types:
1) 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.
2) 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.
The membrane itself is impermeable and stable for decades of use but the risks are sealing the joints and failure of the cavity drain.
Structure is stripped back to the base material and then re-rendered with several coats of a sand/cement render mixed with special damp proofing products.
Used where the likely ingress of water is considered to be less than something that would require the fitting of a DPM. The advantage is that it is vapour permeable and this allows the room to breathe.
Requires a period of curing for around a month before decorating. Any decorative coverings must also be vapour permeable to prevent a build up of humidity within the plaster (known as interstitial condensation)
The risks are in the integrity of the existing masonry, preparation of the surface and correct application of the material and inadequate evaluation of external substrate factors.
Both methods can involve potentially millions of pounds worth of damage in high value buildings.
Long term success can also potentially benefit the client by millions of pounds in built up high value areas in the conversion of previously unused space into high quality occupational use.
The weak links are survey evaluation, application procedures and design details.
Also supervision and unrealistic time scales imposed by clients and poor management on the part of installers can cause problems.
ISSE are evaluating new materials and products for use as follows -
Interlocking gas and water vapour proof panels composed of durable waterproof material fixed directly to the substrate laid over a pore blocking material bonded to the surface.
The design of which could include, as a double protection, a cavity drain facility with mechanical water extraction via sealed drainage system with access points for inspection and maintenance as required and designed.
This system could provide the best of each previous method while removing the risks of each.