Waterproofing of External Basement Walls using Koster Deuxan 2C

Waterproofing of External Basement Walls using Koster Deuxan 2C

Koster Aquatecnic Ltd

This is a BBA-approved system for waterproofing to a structure below ground level, to protect against ground water, moisture, hydrostatic pressure and radon gas, in accordance with BS 8102: 2009.

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For use in:

  • Waterproofing external basement walls.
  • Waterproofing to basement slabs and foundations.
  • Waterproofing to podium decks.
  • Waterproofing to insulating concrete formwork (ICF) basement walls.
  • As an effective vapour and radon barrier.
  • Waterproofing to balconies and terraces.
  • Internal basement waterproofing when in loaded/sandwiched constructions.
  • For waterproofing against hydrostatic pressure.
  • For positive side waterproofing.
  • External waterproofing to lift pits.
  • Waterproofing to pre-cast panels.
  • External waterproofing to bridges, tunnels, and other civil structures.


This BBA-approved positive/ external side waterproofing system can be installed over any mineral substrate, such as reinforced concrete, precast concrete, blockwork, brick and insulated concrete formwork (ICF).

It comprises of the following products:

  • Koster Polysil TG500 – A deeply penetrating primer. When sprayed onto the prepared wall surface, it works to consolidate and strengthen a sandy surface, reduces the absorbency of a mineral substrate, and can also act to immobilise salts within the capillaries.
  • Koster Bitumen Primer – For use when preparing to waterproof over old or existing bituminous coatings.
  • Koster Repair Mortar Plus – This is a fast setting and expanding repair mortar. It is used for making strong and watertight repairs to the substrate, prior to the application of Koster Waterproofing Systems, and for forming fillets at internal junctions. For instance, a 40mm x 40mm concave fillet should be made at all wall to wall and wall to slab intersections. 
  • Koster NB1 Grey - A liquid-applied mineral waterproofing coating which contains crystallizing agents. Suitable for positive side and negative side waterproofing. Koster NB1 Grey possesses excellent pressure and abrasion resistance, as well as chemical and sulphate resistance. When used as a part of this system, it is applied to the bottom area of the basement wall (1 m minimum), over the construction joint and down onto the vertical face of the slab. The NB1 Grey prevents residual water in the substrate or construction joint from interfering with the cure of the primary waterproofing layer. It is brush or spray applied in a single-coat application.
  • Koster Deuxan 2C - A liquid-applied thick film bitumen rubber membrane, which provides a thick, crack-bridging, water and gas proof finish to external basement slabs, walls and podium decks. Koster Deuxan 2C is either hand or spray applied to a primed and prepared substrate to achieve a 4 mm dry film thickness in two coats. Water-based.
  • Koster Glass Fibre Mesh – This is a reinforcing fabric which has an extremely high tear resistance. It is installed between the coatings of Koster Deuxan 2C. It is to be used on all substrates which are likely to be exposed to pressurised water and/ or in danger of cracking.
  • Delta Geo Drain Quattro – A four-layer drainage and protection membrane, to be installed prior to backfill to completely cover the applied waterproofing system and, where possible, should extend from the land drain (at the lowest point) to 150 mm above ground level.

Koster Deuxan 2C satisfies the relevant requirements of NHBC Standards, chapter 5.4 'Waterproofing of basements and other below-ground structures'.  With the use of ancillary and complementary Koster products, it can encompass awkward detailing areas such as expansion joints and pipe penetrations to ensure a full and continuous waterproofing system.

Individual project specific detailed drawings are available along with expert technical advice.

Features and Benefits:

  • Provides waterproof protection to basement walls, foundations, floor slabs, under screeds and in damp proofing situations.
  • Is fully resistant against all forms of ground moisture including soil moisture and retained seepage, hydrostatic pressure, splash water and capillary rising moisture.
  • Crack bridging to 2 mm.
  • Resistant to rain after final coating is applied.
  • Chemical resistance.
  • Radon-resistant at 3mm thick.
  • BBA Approved.
  • Acceptable to NHBC.
  • Polymer modified bitumen coating (PMBC).
  • Liquid-applied.
  • Trowel or spray application.
  • Fully watertight coating.
  • Resistant against positive side pressure.
  • Can be applied to most substrates.
  • Can be applied over old bitumen coatings.
  • 4 mm dry film thickness.
  • Water-based.
  • Two-component.
  • Waterproof against 5 bar hydrostatic pressure.
  • 100% elongation at break.
  • Curing time of approximately 24 hours.

General information


Polymer modified bitumen coating (PMBC)

A cured Polymer Modified Bitumen coating covered with a studded drainage and protection membrane. System designed to be buried below ground.

Studded drainage and protection membrane




Polymer silicate spray primer

M 111 010 Koster Polysil TG500.

Solvent-based bitumen primer

W 110 010 Koster Bitumen Primer.

Cementitious slurry with alkaline silicates

W 221 025 Koster NB1 Grey.

Cementitious repair mortar

W 532 025 Koster Repair Mortar Plus.

Elasticising synthetic dispersion emulsion

W 710 005 Koster SB Bonding Emulsion.

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10 kg drum

Koster Polysil TG500.

10 kg bucket

Koster Bitumen Primer.

25 kg bag

Koster Repair Mortar Plus.

32 kg bucket

Koster Deuxan 2C.

1 x 100 m roll

Koster Glass Fibre Mesh.

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Ten-year product warranty

Uniclass 2015

Ss_32_80_79_30 Fully bonded bitumen membrane external tanking systemsPrimary


J30/110 Cold applied tanking . . . . . .

J20/110 Tanking

Specification data - Fully bonded bitumen membrane external tanking systems Enhanced data

System performance

Design of waterproofing systems





All application surfaces are to be fully cleaned, ideally using a high-pressure waterjet, to remove any shuttering release oils, mud and other contaminates. This should also remove any weak concrete from the surface. Use Koster Repair Mortars to repair any honeycombing or areas of damage as well as for ensuring the surface profile is smooth and even. Check carefully for any cracks or other defects.

All external junctions to be mechanically ground to remove sharp edges and ensure an even application for the system.

Pointing and filling mortar

Koster Repair Mortar Plus.


Koster Birumen Primer.

Koster Polysil TG 500.

Tanking membranes


Waterproof sheets

Koster Deuxan 2C.

Koster NB1 Grey.


Koster Glass Fiber Mesh.



Horizontal protection

Delta Geo Drain Quattro.

Vertical protection

Delta Geo Drain Quattro.

Jointing tape

Koster Joint Tape 20.

Thermoplastic tape for sealing expansion and dilatation joints (up to 12 cm) and broad, irregular cracks. 

Koster Joint Tape 30.

Thermoplastic tape for sealing expansion and dilatation joints (up to 20 cm) and broad, irregular cracks.

Koster Joint Sealant FS.

For expansion joints with a width of up to 35 mm.

Pipe sleeves

Koster Deuxan 2C.


Applying primers for bonded membranes.

Forming junctions between tanking membranes and projecting dpcs or cavity trays.

Installing fully bonded bitumen sheets for tanking.

Installing protection boards.

Installing fully bonded bitumen sheets for tanking.

System completion

Inspection of waterproof coatings and membranes

Layer thickness checks to be made using Koster thickness gauges during installation.  Photographic evidence of installation process and visual inspection of cured layers. A dry test can be carried out upon full cure. A “V” cut can be made allowing the thickness to be measured. Once satisfied, the test area is re-waterproofed as per standard application guidelines.

Third-party certification

BBA Certificate.

Certificate no.: 18/5509i1.

Curing time

24 hours.


Environmental information

Country of product manufacture