Negative Tanking

The installation of a negative waterproofing barrier to an internal surface.

In the absence of the means to install a positive tanking system (waterproof barrier between the outside face of the wall and the ground material against that wall), another option is to install a "negative" tanking system which is the installation of a waterproofing barrier to the "inside" face of the wall. Alternative materials and methodology are used to achieve the waterproofing measures for internal negative tanking.

 

  • As an example of consequential damage and resulting mould growth from ground water movement into a basement level area consisting of a garage, office, small gymnasium and a storeroom, we provide the following photos highlighting the typical type and degree of damage suffered to this part of the structure. The extent of water penetration included ingress of free water through the walls and up through the floor slab.
  • The floor slab consisted of a concrete slab, in some locations dressed up with a floating timber floor and in other areas with a tiled finish. The walls were largely constructed of load bearing masonry with an internal timber framed and plasterboard lining. The damage was enormous, particularly considering that the basement area was constructed less than two years from the date of these photos.
  • As the photos will suggest, the internal timber framing, for the most part bottom plate and lower section of studwork, is seriously water damaged. The same scenario exists with the floating timber floor system.
  • As the photos will suggest, the internal timber framing, for the most part bottom plate and lower section of studwork, is seriously water damaged. The same scenario exists with the floating timber floor system.
  • You will note from these photos, that free water found its way to, and is simply sitting on the concrete slab below the floating timber floor.
  • In areas where the accumulation of water has progressed to be in contact with the timber, wet rot and water damage is prolific.
  • Now to solving the problem! First step was to completely "gut" the interior of this basement area, back to the bare masonry perimeter load bearing walls. And where walls were not located (as in the case of where stud walls concealed the excavated face or the soil and rock escarpment) we needed to construct new structural walls.
  • This was followed by treatment, repairs and preparation of the wall surfaces. The same applied to the now exposed reinforced concrete floor. A multilayer atactic polypropylene membrane was installed to walls and floors, including all detailing. This being Stage 1 only. Note, this is a positive waterproofing technique used in a negative waterproofing situation. Further stages will serve also to reverse this process.
  • Stage 2 involved among other things, a full internal masonry liner to Stage 1 waterproofed structural walls.
  • Stage 3 involved the use of a quartzite based cementitious negative waterproofing hydrostatic membrane with chemicals that crystalised in the pores and capillaries of the subsidiary internal masonry wall of Stage 2.

     

 

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