Frequently Asked Questions

What are the differences between Nitoseal MS600 (MS polymer sealant) and a standard silicone sealant for external building facade joints and when is each the better choice?

Nitoseal MS600 (MS polymer) and standard silicone sealants are both highly flexible, UV-stable, moisture-cure sealants suitable for external building facade joints, but they have different characteristics that make each better suited to specific applications. The key practical differences are paintability, staining tendency, and substrate compatibility. Standard silicone sealants cannot be painted over reliably — water-based and most solvent-based paints do not adhere to cured silicone rubber, and any paint applied over silicone will peel within days to weeks. This means that for facade joints where the sealant joint is painted over to match the surrounding facade colour, standard silicone is unsuitable. Nitoseal MS600 can be painted over (typically after 2 to 6 hours of skin cure to prevent the fresh paint from mixing with uncured sealant) and provides a surface that accepts most paints — this is the most important advantage of MS polymer sealants over silicone in building facade applications where colour matching is required. Silicone staining: standard silicone sealants contain free silicone oil (a low-molecular-weight silicone fluid used as a processing aid) that migrates out of the cured sealant over time and runs down the face of adjacent concrete, stone, or brick, causing dark oily staining that is very difficult to remove. This silicone run-off staining is a common problem on concrete and stone facade panels below silicone-sealed joints. Nitoseal MS600 contains no free silicone oil and does not cause this staining. Silicone sealants are preferred over MS polymer when: the joint will not be painted; the substrate includes surfaces where silicone compatibility is specifically required (certain glasses and coated aluminium systems have tested compatibility with specific silicone grades); and where the joint sealant budget is the primary consideration (standard silicone is generally less expensive than MS polymer sealant).

How does the shelf life and storage requirement of Nitoseal MS600 compare to two-component sealants like Thioflex 600 and what happens if expired product is used?

Nitoseal MS600 is a single-component moisture-curing sealant, and as such its shelf life is limited by the potential for the product to absorb atmospheric moisture through the cartridge closure during storage — if moisture enters the cartridge before use, it will trigger the cure reaction within the cartridge, resulting in a gel or partly cured product that cannot be applied properly. The shelf life of Nitoseal MS600 is typically 12 months from the date of manufacture when stored in a cool, dry location at below 25 degrees Celsius in the original unopened cartridge. In Indian site conditions, the storage temperature requirement (below 25 degrees Celsius) is commonly exceeded on outdoor construction sites in summer — stored in direct sunlight or in a non-temperature-controlled store, cartridge temperatures can reach 40 to 50 degrees Celsius, which significantly accelerates the moisture permeation through the cartridge seal and can reduce the effective shelf life to 6 months or less. Expired or improperly stored Nitoseal MS600 manifests as a cartridge that is difficult to gun (the product has stiffened internally), a product that skins over immediately on the nozzle during application (rapid surface cure from pre-absorbed moisture), or a product that does not achieve the expected flexibility and elongation after application (has partially pre-cured in the cartridge with reduced molecular weight and cross-link density). Using expired sealant in critical facade joints may result in premature joint failure (cracking, debonding, or tearing at low elongation) significantly earlier than the expected service life. Thioflex 600 two-component sealant avoids this moisture-contamination shelf life issue because the base and curing agent are stored separately and do not react until mixed — the two-component system has a longer and more reliable shelf life under site conditions than single-component moisture-cure products.

Does Nitoseal MS600 require a primer before application on common building materials in India such as concrete, brick, and painted masonry and how is adhesion tested before a large job?

Nitoseal MS600, like most modern MS polymer sealants, is formulated to adhere to clean, dry, non-porous substrates without a primer under standard conditions — the MS polymer chemistry includes integral silane adhesion promoters that bond to the silica groups present on the surface of concrete, brick, mortar, natural stone, glass, and most metal oxides (aluminium, steel). In standard Indian building facade joint conditions on new construction — clean concrete panel joints, brick expansion joints, and aluminium curtain wall perimeter joints — primer application before Nitoseal MS600 is generally not required. However, primer application is recommended or required for: very smooth, dense concrete or stone surfaces (highly polished granite or marble, for example) where the surface area for adhesion is very low and the surface energy may be insufficient for reliable peel-strength development without a coupling primer; painted surfaces where the sealant bonds to the paint film rather than to the substrate — if the paint is well-bonded to the substrate, the sealant-to-paint adhesion may be adequate, but if the paint is poorly adhered, the sealant will pull the paint from the substrate during joint opening and the joint will fail cohesively within the paint film; and in high-movement or structurally critical joints where the maximum achievable adhesion is required and a primer provides additional confidence in long-term bond retention. To test adhesion on a specific substrate before committing to a large-scale application, a simple H-block or peel adhesion test should be performed on site: apply a bead of Nitoseal MS600 to the cleaned substrate, allow to cure for 7 days, then peel back by hand — if the failure mode is cohesive (within the sealant body), adhesion is adequate; if the failure is adhesive (at the sealant-to-substrate interface), primer is required. The Fosroc technical representative or Space Arc Engineering can advise on the specific primer required for challenging substrates.