Bostik N40 Primer

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Bostik N40 Primer is a fast-drying, clear, and non-staining solvent-based primer/cleaner, specially designed to enhance the adhesion of polyurethane sealants and waterproof membrane systems on non-porous substrates, including rigid plastics and various metals. It is a one-part product, eliminating the need for mixing.


  • Promotes high bond strength of polyurethane sealants, acrylic sealants, and waterproof membrane systems on non-porous substrates
  • Fast-drying formulation
  • Clear appearance


  • Colour: Clear
  • Size: 1 Litre


Bostik N40 Primer is ideal for use with the following Bostik polyurethane sealants requiring adhesion to non-porous substrates:

  • Bostik Seal ‘N’ Flex® 1
  • Bostik Seal ‘N’ Flex® FC
  • Bostik Fireban® One
  • Bostik Matrix® FC

Additionally, Bostik N40 Primer can be applied on the following substrates:

  • ABS rigid plastics
  • uPVC rigid plastics
  • Brass
  • Bronze
  • Copper
  • Mill finished aluminum
  • Anodized aluminum
  • Bright steel
  • Galvanized steel
  • Stainless steel
  • Gel-coated fiberglass


Before applying Bostik N40 Primer, ensure the substrate is sound, dry, clean, and free from any dust, residue, or contamination. It must meet the requirements of substrate preparation as specified in the applicable Polyurethane Sealant Technical Data Sheet.


Follow the Two Cloth Method to apply Bostik N40 Primer effectively:

  1. Dampen a clean cloth with Bostik N40 Primer and spread it evenly over the non-porous substrate using a cleaning/rubbing action.
  2. Immediately wipe off all primer residues with a buffing action using a second clean cloth.
  3. Allow the substrate to dry for a minimum of 5 minutes before installing the backing rod, sealant/adhesive, or waterproof membrane system.
  4. Do not leave the primer longer than 4 hours before applying sealant/adhesive.
  5. If 4 hours have elapsed without applying sealant/adhesive, re-prime the surface.


  • Provide adequate ventilation during application.
  • For use on non-porous rigid plastic, ferrous, and non-ferrous substrates only.
  • Avoid application on unpredictable absorptive surfaces such as marble, limestone, or granite, unless a standard of appearance has been agreed upon based on testing for stain and/or discolouration.
  • Ensure no free or ponded water or condensation on the substrate before applying the sealant/adhesive or membrane system.
  • Re-prime the surface if affected by rain, dust, or other contaminants after application.
  • Use only on recommended substrates, refer to the substrate primer guide.
  • Do not dilute or mix with other solvents or primers.

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Bostik N40 Primer

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