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A single component, low viscosity, self-wetting, butyl blend mastic designed to be used in conjunction with roofing and waterproofing systems. It is an extremely tacky material and is primarily used as a sealing agent between various membranes and when they are terminated using a compression type seal.

Standard product features



Technical properties:

  • Flash point: 4°C.
  • Solids: 80%.
  • Specific gravity: 1.29.
  • VOC: 250 g/L.

NBS Specification

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This product is associated with the following NBS Create clause:
45-55-75/325 Butyl rubber construction joint sealants

Product specification

An important note about specifying



Flex-R Ltd


+44 (0)1494 448792

Product reference

Water Cut-Off Mastic

Manufacturer details

Sandswood House,
Hillbottom Road,
Sands Industrial Estate,
High Wycombe,
Buckinghamshire, HP12 4HJ
Tel +44 (0)1494 448792
Fax +44 (0)1494 858433
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