About Sika Sarnacol-2142 S

Sarnacol-2142 S is Sika’s workhorse bonding adhesive for fully adhered single-ply roofing. It is a one-part liquid that cures by reacting with atmospheric and substrate moisture, so there is no mixing, no pot-life clock and no waste from part-used two-component kits. Contractors roller it directly onto the deck, wait for the solvent to flash off until the film turns tacky, and then roll the felt-backed membrane into it. Because the felt scrim on the underside of Sarnafil G, Sarnafil T and Sikaplan membranes grips into the curing polyurethane, the finished bond is both chemical and mechanical, which is exactly what gives an adhered roof its wind-uplift resistance.

For an Indian project team, the appeal is versatility across the substrates you actually meet on site. The same tin bonds to structural concrete, plywood and timber decking, fibre cement, torch-applied bituminous underlays, metal and sandwich panels, and to insulation boards such as EPS, PIR and mineral fibre. It tolerates surfaces that are dry or only slightly damp, which is realistic for roofs that see morning dew or an interrupted monsoon-season programme. As part of a Factory Mutual-approved Sarnafil build-up, it is a specification-grade product rather than a generic mastic, and Space Arc supplies it as an authorised Sika channel partner with the technical back-up to match.

The technical insight

The mechanism is what separates this from an ordinary contact cement. Sarnacol-2142 S is a moisture-triggered polyurethane: the free isocyanate groups in the resin react with water vapour drawn from the air and from the substrate, cross-linking the film into a tough, flexible solid that keys into the membrane’s felt backing. That is why the adhesive works on slightly moist decks where a purely solvent-evaporation glue would struggle, and why the bond keeps building strength for hours after the sheet is laid. In practice the applied film flashes off first to a tacky, string-free surface, and it is into that window that the membrane must be placed and rolled. The trade-off is discipline: humidity and temperature drive the reaction, so the coating must be consolidated with pressure before it skins over, and cold or bone-dry conditions slow the cure. Get the timing right and you have a fastener-free roof whose holding power comes from the chemistry of the interface, not from mechanical points that can telegraph, corrode or leak.

Where it is used

• Fully adhered Sarnafil G and Sarnafil T felt-backed PVC membrane roofing
• Bonding Sikaplan felt-backed single-ply membranes on flat and low-slope roofs
• New warm-roof build-ups over PIR, EPS and mineral-fibre insulation boards
• Re-roofing and overlay works where mechanical fastening is undesirable
• Adhering membranes to structural concrete and screeded roof decks
• Bonding over plywood, timber and OSB decking on lightweight roofs
• Membrane adhesion to metal and insulated sandwich roof panels
• Detailing and field bonding over torch-applied bituminous underlays

Key advantages

• One-part and ready to use, so there is no mixing, no pot-life and no two-part wastage
• Moisture-curing chemistry bonds even to clean, slightly damp substrates
• Simple roller application suits large, open roof fields and skilled site crews
• Adheres to a wide range of decks, insulations and underlays from a single product
• Fastener-free adhered system improves wind-uplift performance and avoids point leaks
• Factory Mutual-approved when used within the specified Sarnafil roofing system
• Combined chemical and mechanical grip into the membrane’s felt backing
• Proven track record over decades of Sika single-ply roofing installations

Limitations & considerations

• Only for felt-backed membranes; it will not bond smooth-backed or non-Sika sheets reliably
• Minimum +5 C ambient and substrate temperature; cold conditions delay or prevent cure
• Solvent-borne and flammable, so it needs good ventilation and no ignition sources
• Limited open time means only the area that can be membraned within roughly 15 minutes should be coated
• Not a waterproofing layer in itself; it bonds the membrane but the sheet does the sealing
• Shelf life is about 9 months, so old or part-used tins should be checked before use

Selection & best practice

Specifications

Industry use cases

How we position Sika Sarnacol-2142 S

Sarnacol-2142 S is a system component, not a standalone product, so it is best specified alongside the rest of the Sika single-ply family: the Sarnafil G and Sarnafil T felt-backed membranes it is designed to bond, Sarnafil detailing sheet and profiles for upstands and terminations, and Sikaplan felt-backed membranes for value-engineered adhered roofs. Where a project specifies mechanically fastened rather than adhered zones, or needs pourable and cold-applied alternatives at perimeters, those are separate Sika roofing adhesives and accessories that our team can pair with it. Outside the roofing membrane world, buyers on the same project often need liquid-applied waterproofing for wet areas, basements and podiums, and for those we cross-sell across our other brands, including Fosroc’s Nitoproof and Brushbond ranges and Dr. Fixit membranes. There is no genuine Fosroc equivalent to this membrane adhesive itself, so we do not substitute one; for adhered Sarnafil and Sikaplan systems, Sarnacol-2142 S is the correct and specification-compliant choice.

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