Basement Tanking

Basement tanking is needed to combat a condition known as lateral penetrating damp. This occurs when the soil levels against an external wall are higher than the building so moisture can penetrate the internal basement, whether it is a basement or ground floor below the external ground levels. Effects can be more dramatic in basements, vaults and coal cellars, especially where no precautions have been made for dampness. Basement tanking in London is often needed to overcome issues caused by damp in older buildings and poorly waterproofed basements and cellars.



There are two main solutions to effectively tank basements and earth retaining walls.


Cementitious Tanking: Type A Waterproofing

Comes in many different forms although they generally do the same thing. They form a barrier system to prevent the ingress of groundwater.

Waterproof render, waterproof slurries and epoxy resin systems tend to be our product of choice when we are specifying a cementitious, however, we have a wide variety of products and suppliers to help us choose the best product for the job.

They are also widely used on ground floor properties for rising dampness.

Installation & Functioning:

Waterproofing render system: The internal walls are prepared and taken back to the base material (i.e. brick) before applying a sand and cement render splatter coat followed by a multi-coat render all of which will be combined with the appropriate waterproofing agent, i.e. Sika 1. The render will provide a watertight seal that will prevent ingressing water affecting the internal face of the wall. The treated walls can be left as a raw render finish, or more commonly for areas used as living space, a skimmed plaster finish is applied to the render, or alternatively dry lined.


Membrane Sealed Tanking or Water Management System: Type C Waterproofing

Used when higher or unpredictable levels of water ingress occur, e.g. basement areas.

Suitable for rooms where it is not advisable to use cementitious tanking due to hydrostatic pressure (changes in pressure may undermine the stability of the wall).

Allows ingressing water to channel behind the membrane into perimeter channels that drain into to a sump and pump where the water is then pumped away from the building.

Advantages of this system are that it places no additional strain on the building, it is easily maintained and often less disruptive, with less waste produced during the works process.

Best suited for under road vaults and basements where high volumes of groundwater are expected, or where there is heavy surface traffic above ( e.g. a busy road).


Installation & Functioning:

The membrane is installed in the walls (and floors or ceilings where applicable) using specialised plugs. Goods such as meter panels and pipework are sealed to the membrane using pre-prepared plugs or plyboard. Perimeter channels are then installed around the base of the floor or wall area. These channels will allow ingressing water restricted behind this cavity membrane to drain into a sub-floor sump and pump; the water is then pumped away from the property to an appropriate existing drain. The system will be finished to a high standard with plasterboard and a skim finish to walls and ceilings, ready for decoration by your contractor.


Membrane Ventilated Systems:

Cavity membrane is sometimes used in situations above ground where no free-running water is expected (e.g. when external decking or patios cause high ground levels).

The membrane will have an air gap at the top and bottom, providing a dry internal surface that prevents damp and salt contamination that can be damaging to decorative plaster.

For further information, please do not hesitate to contact us. Or alternatively, book a free survey to ascertain if the above systems would be suitable for you, and receive a report detailing a full specification catered to your property.

A professional remedial survey is highly recommended as mistakes in diagnoses are commonplace; errors can result in unnecessary and costly works that may fail to control the dampness. At Garratt’s, we pride ourselves on providing our clients with honest and impartial advice.

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