External Systems

Earth retaining structures are at risk of being damaged by moisture penetration from the outside or by the ground water under hydrostatic pressure.


External systems were thought to be the only thing that was required to fully waterproof a structure; however the new guide to waterproofing structures under the ground BS8102 states that two forms of waterproofing are required.


 The most reliable external system would be a four layer system which comprises of a layer of paint on or spray on Bitumen type product and then a three layer membrane system applied over the top of the bitch. The membrane is made up of a slip coat, studded membrane then a geotextile layer.

Alliance are a proud installer of DELTA® Membranes which are available as geo-composites to deal with such problems. They add a layer of protection and a layer of waterproof drainage, together which will quickly remove the water to a suitable land drainage around the structure. These can be installed with up to 10 metres in depth.

Basement Waterproofing Solutions | AllianceThey prevent the build up of hydro static pressure on the structure and filter the water via an internal polypropylene filter layer.

This in turn will prevent fine ground particles from causing blockages in the drainage facility and will avoid destabilising the surrounding soil. These membranes also act as a protection layer against any primary waterproofing (type A waterproofing) on the structure and against damage when the backfill takes place.

You would then install a perforated pipe (French drain) at the base of the wall (the pipe can be supplied pre rapped in geotextile cloth). The pipe will then be covered with stone chips/ pea gravel to allow the water to percolate down to the pipe below, by using chips rather than soil the pipe will not clog as quickly and extend the life of the perforated pipe.

The main reason for this type of installation not being a standalone system is that the pipe can’t be serviced easily if at all.

Another important factor to remember is that the BS8102 recommends a fully qualified basement waterproofed is on the design team before any designs are considered.

Typical detail of our external waterproofing

Basement Waterproofing Solutions | AlliancePrimary waterproofer is first applied to the external wall, lapping over the foot of the foundation using Koster Deuxan 2C, KSK SY 15 peel & stick membrane or Koster 21. 

Second, this is then covered by the Delta-Geo-Drain-Quattro, NP-Drain, MS-Drain or Terraxx, which is a waterproof, protection and drainage layer. The purpose of this is to protect the primary waterproofing when the backfill takes place, relieving the hydrostatic pressure from the structure by draining the groundwater down to the perforated land drain pipe. This groundwater is then taken off to a soak-away or sump chamber.

The open top edge of the membrane is capped off using Geo-Drain Clips and MS-Profile or Terraxx Profile, when using insulation. The backfill is then put in place. See below the external waterproofing video using our NP-Drain.