Selleys 410g N-Mastic Sealant Off White | Permanently Flexible | Australia

When a sealant needs to perform in concealed joints and confined spaces where future access for maintenance is difficult or impossible, choosing the right product matters enormously. Selleys N-Mastic Sealant is a non-skinning, poly-butene based compound engineered to remain permanently flexible — never hardening, never cracking, and never losing its sealing integrity over time. Whether you’re sealing lap joints in construction panels, insulating against moisture vapour, or bridging connections between dissimilar materials, N-Mastic delivers a dependable, long-lasting barrier that moves with the structure rather than against it.

Unlike conventional sealants that cure to a rigid or semi-rigid state and can crack under movement or thermal stress, Selleys N-Mastic stays workably flexible for the life of the installation. Its non-skinning formulation also means it remains receptive in concealed applications where air exposure is limited — a critical advantage in lap joints and sandwiched panel assemblies where curing-dependent sealants may never fully set. Combined with its microbe-resistant formula, low shrinkage characteristics, and broad temperature tolerance, N-Mastic is the professional’s choice for demanding moisture-barrier sealing applications.

Key Highlights

• Permanently Flexible, Non-Hardening Formula — Based on poly-butene polymer chemistry, this sealant never fully hardens or becomes brittle over time, maintaining its flexible, conforming seal indefinitely — ideal for applications subject to movement, vibration, or thermal expansion and contraction.
• Excellent Moisture Vapour Barrier — Formulated specifically to serve as a highly effective barrier against moisture vapour transmission, protecting concealed structural elements, insulation panels, and building materials from the damaging effects of moisture ingress.
• Non-Skinning in Concealed Applications — The non-skinning poly-butene base remains active in confined, low-air-exposure environments such as lap joints and sandwiched assemblies where conventional curing sealants may fail to fully set.
• Microbe-Resistant Formula — Contains microbe-resistant properties that inhibit the growth of mould and bacteria within the sealant, maintaining hygiene and long-term integrity in applications where biological growth could compromise the seal.
• Good Adhesion to Most Substrates — Bonds effectively to a broad range of common construction and manufacturing materials including plastics, metals, timber, glass, masonry, and expanded foam panels — minimising the need for surface primers in most standard applications.
• Low Shrinkage — Minimal shrinkage during and after application ensures the sealant maintains full contact with both substrate surfaces across the joint, avoiding voids or gaps that could compromise the moisture barrier over time.
• Wide Temperature Tolerance — Withstands temperatures ranging from -40°C to 80°C, making it suitable for use in environments subject to significant temperature variation, including construction cavities, roof assemblies, and industrial panel applications.

⚠️ Application & Safety Notes:

• For indoor use only — not suitable for exterior or fully exposed outdoor applications.
• Ensure joint surfaces are clean, dry, and free from dust, grease, and loose material before application for optimum adhesion.
• Not intended for use as a structural adhesive — for sealing applications only.
• Use in a well-ventilated area — solvent-based synthetic polymer formula releases vapours during application.
• Wear appropriate PPE including gloves and eye protection during application.
• Keep out of reach of children.
• If eye contact occurs, rinse thoroughly with water and seek medical attention immediately.
• Store in a cool, dry place with cap tightly sealed to prevent product from drying out.

⚠️ Compatibility Warning: Intended for concealed lap joint sealing only. Not recommended for exposed external surfaces, continuously wet areas, or structural bonding applications. Always confirm suitability for specialty substrates before full application.

Technical Specifications