Continous Exterior Water Isolation / Dampproofing at Raft Foundations (Basement Tanking)

The most descriptive illustration I found is the one below:

  1. The red stripes are special dampproofing materials. Because the raft foundation and shear walls are constructed one after another; the adherence in between cannot be guaranteed and a joint is formed which is called a "cold" joint (the grey line in between). Water can penetrate from this joint and to prevent that, a special insulation material that expands when met with water is applied here. This type of isolation is also necessary if for some reason we create holes on the shear wall.
  2. One other insulation required on the shear wall is applied to close holes on the wall which are leftovers of forming work. Cementitious material is applied to these holes which does not change its size (shrink) when freezes.
  3. The blue layers are the actual water isolation layers. The most common type is in the form of bituminous roll sheets as can be seen in below photo:

  4. Please notice that a portion of the formwork is already applied to the perimeter, and the water isolation is already applied to the forming as well. This is required to stitch the edges of dampproofing with the water isolation applied on the shear wall so the whole of the system is packed with a water barrier (bohçalama).
  5. You have to protect the dampproofing both on the horizontal surface and the vertical surface. A 5-8cm. thick screed is applied on the horizontal surface while a 5-8 cm. hardform insulation material is used on the vertical surface (indicated with green layer). The outmost layer is a special HDPE sheet which also provides some drainage
  6. The center of the drainage pipe must be no higher than the bottom of the raft foundation.
An even better example of this detail is shown below, the difference from the above example is that the rubble concrete forms a parapet at the perimeter of the raft foundation:


You have to apply a three-layer filling over the drainage pipe and separate each layer with a geotextile material (a special material which can let water but prevent different fill layers from mixing establishing structural integrity between fill layers) as listed below (listed from bottom to top):
  1. A filtration layer fill - typically sand (50~100cm. according to depth) 
  2. A fine aggregate fill (50~100cm. according to depth) 
  3. A coarse aggregate fill (Rest of the depth)
  4. Soil (as required by landscape architecture, 10~100cm.)

Last (but not least) you have to think a detail for the skirting of the building. That is, where the outer walls meet with the ground. Google "subasman detayı" for details...

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