Selleys N-Mastic is a non-skinning polybutene-based compound. It will remain permanently soft and paste-like.



  • Non-hardening - remains permanently flexible to provide a lasting seal
  • Good adhesion - adheres well to most substrates
  • Moisture resistant - provides an excellent barrier to water vapour transmission
  • Resists microbial attack
  • Low shrinkage - avoids the risk of sealant pulling away from joint surfaces
  • Wide service temperature range - withstands –40°C to +80°C service conditions

Where can this product be used?

  • Sealing concealed lap joints between plastics, metals, timber, glass, masonry, and expanded foam panels.
  • Installation of cool rooms, prefabricated construction and gasket sealed windscreens to exclude draughts and water penetration through joints in materials.

What materials is this product suitable for?

  • Glass
  • Masonry
  • Metals
  • Expanded foam panels
  • Timber 
  • Plastics

Please contact your store to confirm avaliability, as some stores may have a limited range.

Size 410g Cartridge
Colours Off White
Technology  Solvent Based
Use  Interior 

The following should only be used as a guide and the installer should apply all Australian Standards, BCA/NZBC requirements, and best practices when installing. Use ony in a well ventilated area. Avoid contact with skin and eyes and breathing vapours.

  1. Surfaces to be sealed must be clean, dry and free from dust, grease and flaking paint.
  2. Clean surfaces with mineral turps and allow to dry.
  3. Cut nozzle supplied at an angle and to the required opening. Cut end off nipple on cartridge, fit nozzle and insert in suitable caulking gun such as the Selleys Light Speed Caulking Gun.
  4. Using the caulking gun, apply N-Mastic to the joint and tool if necessary.
  5. Mechanically fix joints where necessary.


  • Due to the non-skinning, non-hardening nature of the sealant, N-Mastic should not be used in exposed joints where dirt pick-up or hand contact can be a problem.
  • As N-Mastic is not elastomeric, it should not be used in areas subject to considerable dynamic stress.
  • N-Mastic is not recommended for sealing lap joints in mobile homes, truck bodies, etc., as significant vibration and flexing occur during travel. 
  • Although N-Mastic is resistant to static pressures, a curing sealant is recommended where this is a critical factor.
  • Spills and tools can be cleaned up with mineral turps. 

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