Waterproofing of Basement Slab using Koster KSK SY15 Membrane

Koster Aquatecnic Ltd

This is a certified system for waterproofing to a concrete slab below ground level, to protect against ground water, moisture, hydrostatic pressure and radon gas. In accordance with BS8102: 2009.

Jump to:
+44 (0)1387 270252 www.kosteruk.com


  • Waterproofing to basement walls, including external basement and IFC walls.
  • Waterproofing for foundations, floor slabs under screeds, basement and below ground slabs and foundations.
  • Internal basement waterproofing when in loaded/ sandwiched constructions.
  • Resistant barrier against ground moisture, including: soil moisture and retained seepage, hydrostatic pressure, splash water and capillary-rising moisture.
  • Effective vapour and radon barrier.
  • Waterproofing to balconies, terraces and podium decks.
  • Waterproofing against hydrostatic pressure.
  • Positive side waterproofing.
  • External waterproofing to lift pits.
  • Waterproofing to precast panels.
  • External waterproofing to bridges, tunnels, and other civil structures.


This waterproofing and gas protection system benefits the design and installation of basement and below ground slabs. The system incorporates a high-performance, cross-laminated, self-adhesive bitumen membrane which offers high puncture and tear resistance as well as the ability to resist ground water/ moisture and radon gases.

The Koster below slab system consists of the following products:

  • Koster KBE Liquid Film – Highly elastic water-based bitumen/ rubber liquid waterproof coating. Koster KBE Liquid Film can be diluted 2:1 with water, and applied to a mineral substrate to act as a high-performance primer, and used undiluted as a seam/ overlap sealer and detailing compound. When used as a primer, it is rolled or brushed onto a prepared substrate. As a detailing coating, it is brush or trowel-applied.
  • Koster Fix Tape 15 SY – 200 mm wide cold-applied, self-adhesive sealing strip made from bitumen/ rubber. This tear-resistant tape is cross-laminated, and once installed, is immediately water-proof and rain-proof. Used as a perimeter tape, it provides a connection between the vertical and horizontal sections of the basement slab, and a connection for the primary external waterproofing on basement walls. See 'Waterproofing of External Basement Walls using Koster Deuxan 2C'.
  • Koster KSK SY15 – This cold-applied self-adhesive bitumen rubber membrane is the core to the overall below slab waterproofing system. Supplied in large 1.05 x 20 m rolls, it simplifies on site installation and speeds up construction, as it is immediately waterproof, and offers maximum protection against all forms of groundwater and radon gas. 

This multi-layered system satisfies the requirements of NHBC Standards, Chapter 5.4 'Waterproofing of basements and other below ground structures to all grades'.  Used with 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.

Features and benefits:

  • Radon-resistant.
  • Resistant to hydrostatic pressure.
  • Resistant against positive side pressure.
  • Crack-bridging to 2 mm.
  • Instantly watertight and rainproof.
  • Fully watertight coating.
  • Acceptable to NHBC.
  • Easy application.
  • Can be applied to most substrates, including over existing bitumen coatings.
  • Self-adhesive membrane.
  • 1.5 mm overall thickness.
  • Water-based primer.


The application for the system components should be carried out as below:

  • Site Preparation of Basement Raft Slab:

Excavate and level the site. 

Lay geotextile over the levelled ground to cover footprint of basement.

Compact hardcore to give firm base, and overlay with polythene sheet.

Construct formwork to extend to entire basement footprint and to full height of completed basement raft slab.

  • Application of Perimeter Tape:

Using Koster Fix Tape 15 SY, score release paper on back of tape using a knife, and staple to the bottom inside face of the installed formwork. Install with self-adhesive side facing inwards. Remove bottom layer of release paper, exposing 100 mm of the bitumen adhesive.

  • Blinding layer

Install 100 mm thick unreinforced blinding layer and leave with a floated finish.

  • Priming:

Mix Koster KBE Liquid Film 2:1 with clean water and, using roller, paint 200 mm wide band around edge of cured blinding layer. Allow to go tacky. Remove release paper from top half of Koster Fix Tape 15 SY, and fold down onto primed blinding layer. Use roller to ensure that it is well adhered to the concrete.

Continue to prime remainder of concrete blinding layer, using Koster KBE Liquid Film 2:1 diluted with clean water roller, applied as above. Allow to go tacky.

  • Waterproofing installation:

Using Koster KSK SY15 Membrane, overlap with the already adhered Koster Fix Tape 15 SY tape. Remove release paper from the edge, and using a roller, ensure it is well bonded to the fix tape. Next, unroll entire membrane so it sits flat on the concrete blinding layer. Slowly peel away release paper from under the membrane, and use roller to ensure membrane is fully adhered to priming layer. There should be no bubbles or large ripples in the membrane. Overlaps between sheets are to be 100 mm.

  • Seam Sealing:

Use Koster KBE Liquid Film un-diluted and brush or trowel over overlaps and into any detailing.

  • Protection:

Prior to rebar placement, provide protection to installed membrane. This can achieved by either installing 50 mm unreinforced screed, or by laying insulation boards. It is important to note that the insulation boards must be below-ground rated and of suitable compressive strength.


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

General information



A black smooth bitumen sheet membrane with an HDPE top layer. System designed to be buried below ground or encased between concrete layers.




Bitumen rubber membrane

W 815 105 – Koster KSK SY15 – Self-Adhesive Bitumen Rubber membrane.

Bitumen rubber tape

W 815 002 – Koster Fix Tape 15 SY – Self-Adhesive Bitumen Rubber Tape.

Bitumen rubber liquid coating

W 245 024 – Koster KBE Liquid Film – Water-based bitumen Rubber liquid coating.


1.05 x 20 m

W 815 105 – Koster KSK SY15 - Roll size.

0.2 x 20 m

W 815 002 – Koster Fix Tape 15 SY - Roll size.

24 kg

W 245 024 – Koster KBE Liquid Film - Bucket size.


Ten years

All materials mentioned are covered by the Koster 10-year product warranty.

Uniclass 2015

Ss_32_20_30_15 Cold-applied liquid floor damp-proofing systemsPrimary


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

Specification data - Cold-applied liquid floor damp-proofing systems Enhanced data

System performance

Conforms to BS EN 13969: 2004.





Floated concrete finish to blinding layer.

Pointing and filling mortar

Cement-gauged designed mortars.


Bitumen primers.

Koster KBE Liquid Film – Diluted.

Damp proof coatings


Coating materials

Cold-applied bitumen solutions.

Koster KBE Liquid Film. 


Self adhesive, bitumen membrane.

Koster KSK SY 15.


Applying primers for self-adhesive tanking sheets.

Installing corner reinforcement for self-adhesive tanking sheets.

Installing fully bonded bitumen sheets for tanking.

Installing preformed collars for pipes, ducts, cables through flexible sheet waterproofing.

Installing protection boards.

Preliminary installation.

Preparation of substrates for flexible sheet tanking.

System completion

Inspection of damp-proof coatings and membranes.

Any ripples or air bubbles are to be cut with and re adhered. Oversized patches using Koster KSK SY15 are to be placed to cover the defect and Koster KBE Liquid Film used to over coat.

Environmental information

Country of product manufacture


Similar products from Koster Aquatecnic Ltd