Liquid applied multi-purpose waterproofing coating: KÖSTER 21

KÖSTER officially introduces the R&D Department´s latest innovation: KÖSTER 21

Standing for “waterproofing in the 21st century” the product´s name expresses the fact that the product combines many advantages from different waterproofing materials and can therefore be applied in a very broad range of applications. KÖSTER 21 has been designed around a number of key requirements which the world-wide waterproofing market today and in the near future demands from successful waterproofing solutions:


  • Solvent free
  • VOC free
  • Polymer based,
    no isocyanates or bitumen
  • Two component, fast curing
  • White color, reflects sunlight and heat (reducing necessity for cooling)

Technical characteristics

  • Elastic and crack bridging
  • Resistant to pressurized water
  • Suitable for indoor and outdoor use: UV-resistant, resistant against salts, hydrolysis, frost
  • Excellent adhesion also to moist mineral substrates
  • Good bonding to a broad range of different substrates, like concrete, metal, wood or old waterproofing materials ( e. g. bitumen)
  • Density of 1.55 g / cm³


  • 1.3 mm total layer thickness
    (2 layer application)
  • Liquid and therefore seamless applied
  • Very easy application by
    brush, roller, trowel or spray application possible.
    The consistency can easily be adjusted by adding up to 8% of water
  • Application temperature
    +5 °C to + 35 °C

Tests & Certifications

  • Carbon Dioxide diffusion
    (test certificate available)
  • EN 1504-2 (work in progess) surface protection systems for concrete
  • DIN 18195 (work in progess) waterproofing of constructions



Fields of application

The technical characteristics and the excellent workability of the material provide the base for a very broad range of application areas: KÖSTER 21 can be used for the positive side waterproofing of basements, underneath tiles (e. g. in wet rooms), balconies and terraces, roofs, water tanks and applications which are similar to these. The very good bonding properties allow the application as a repair material on old waterproofing materials. Apart from waterproofing KÖSTER 21 can be used as a carbonation retarder for the protection of concrete structures. The material is furthermore suitable for the protective coating against synthetic oils and aliphatic hydrocarbons (up to 2 bar). Please consult with our technical department (Mr. Samuel Tsibu Sarpong: click here for contact form) for specific inquiries.

Application case study:

Substrate preparation: dust, lose particles and bonding inhibiting materials have to be properly removed. Only salt burdened or absorbent substrates have to be primed. Voids greater than 5 mm have to be repaired and junctions have to be rounded out using KÖSTER Repair Mortar Plus.
The first layer of KÖSTER 21 is applied with a minimum consumption of 1 kg / m². In Areas which are in danger of cracking KÖSTER Flex Fabric or KÖSTER Glass Fiber Mesh is embedded into the fresh first layer. In roof areas a mesh has to be embedded always.
On waterproofing areas like terraces, balconies or roofs different materials have to be embedded into the waterproofing layer. For example metal railings or plastic drainages. Embedding a plastic drainage: The concrete substrate and the plastic drainage show different bonding and thermal expansion / contraction characteristics a mesh has to be embedded in these areas.
The second layer of KÖSTER 21 is applied with a minimum consumption of 1 kg / m². Total consumption is 2 kg / m² leading to a minimum layer thickness of approx. 1.3 mm. The finished surface, waterproofed with KÖSTER 21.

Please click the following link for: the KÖSTER 21 product page

Please click the following link for a: contact mail to our sales or technical department




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