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"Preserving the past for our future"


Tanking is a specialist waterproofing system applied to the face of a structure, on the positive side or the negative side. It is designed to prevent any lateral penetration of moisture, either by capillary action or hydrostatic pressure. Its most common usage is in cellars and basements, it is also used in buildings with split levels of flooring.

The application of tanking can transform a damp and uninhabitable redundant area into a functional accommodation space. This extra space can add greatly to the value of the property and can be achieved without impacting on the overall footprint of the building.

We received a phone call requesting a survey and quotation to waterproof a damp basement room. The property was a detached domestic dwelling circa 1930, situated in the Home Counties borders. The client informed us that the room had a history of water penetration through the walls as well as standing water on the floor following periods of heavy rainfall. The floor was covered in terracotta tiles and the walls were bare brickwork. The area was being used as a storage facility and the client wished to turn it into a multi-purpose habitable space.

Case Study - Tanking / Structural Waterproofing to a Basement Room

Tanking Materials

Some of the component materials of the cavityThe bare wall detail prior to tanking

Bare Brick Wall Before Tanking

An appointment was arranged for our surveyor to visit the property and to discuss the possible options with the client. Given the current site conditions and the history of high water table levels, our surveyor’s recommendation was that a cavity drain membrane tanking system be installed to the walls and floor. To compliment the system also that a sump be dug in the floor and a submersible pump be installed to remove the excess water to a suitable drainage point. Also discussed with the client were the options with regards the various finish specifications for the walls and floor. The client expressed a preference for a finished screed for the floor and a skimmed up dot-and-dab plasterboard finish to the walls. A quotation was prepared and emailed to the client. Several weeks later we received a phone call requesting an on-site meeting to run through the report and make a few minor alterations to the specification.

The schedule of works began with digging a trial hole in the concrete floor in order to ascertain its specification. Beneath the terracotta tiles there was a 2 inch screed sitting on just earth and without any form of waterproof membrane. After a discussion with the client it was agreed that we would dig up the existing floor and relay it to Central Conservation’s modern solid floor specification. Digging down had the added advantage of being able to gain an extra couple of inches head height. A new solid floor was installed up to slab level, incorporating perimeter drainage channels and a sump which would house the pump unit.

Tanking Pump Alarm System

A high level alarm was added to the pumpInstalling the system

Tanking Membrane in Place

Next the walls were prepared to receive the membrane system, this was installed to the manufacturers specifications using the proprietary fixings and sundries. The wall membrane specified has an 8mm stud and comes with a mesh attached in order to provide a key for installation of the dot-and-dab plasterboard finish. The wall membrane was taken down to a point where it could be overlapped and joined with the floor membrane to provide a sealed finish. At this point the client’s electrician was able to install the cabling for any electric sockets etc, as this would then be inserted through the plasterboard for ease of fixing.

A detail showing the floor to wall join of the membrane system

Tanking Floor to Wall Joint

With the floor slab installed a 20mm stud floor membrane was laid and was sealed where it met the wall membrane. A concrete screed was then laid on the floor membrane. The sump pump in its customised container was then fitted, the plumbing and electric runs and airtight manhole cover having been prepared earlier to accept the installation. The client also opted for a back-up battery alarm which would activate in the event of a power failure. The plasterboard walls were then skimmed up ready for decoration. Our operatives then thoroughly cleaned up the area.

The area is now being used as a customised playroom for the client’s grandchildren.

Back to top The plasterboard and skim finish in the basement

Tanking Drying Out