Frequently Asked Questions

What is the difference between Dr. Fixit MP Sealant (acrylic) and Dr. Fixit Tileseal (silicone), and which should be used for sealing the gap around a new aluminium window frame in an external masonry wall?

Dr. Fixit MP Sealant and Dr. Fixit Tileseal represent two fundamentally different sealant chemistries — acrylic emulsion and silicone elastomer — with distinctly different performance profiles, and choosing the right product for the window frame application requires understanding these differences. Dr. Fixit MP Sealant (acrylic emulsion): Acrylic sealants cure by water evaporation rather than chemical crosslinking, producing a relatively rigid, low-modulus film rather than a true rubber. The key advantages of acrylic are paintability (silicone cannot be painted — paint does not adhere to cured silicone surfaces) and lower cost. The key limitations of acrylic sealant are: limited movement accommodation (plus or minus 15 percent of joint width versus plus or minus 25 percent for silicone), vulnerability to water before cure is complete (rain within 4 hours of application on external joints washes the sealant out of the joint), and tendency to harden and crack over long-term outdoor UV exposure as the acrylic film degrades. For external joints subject to significant thermal movement between dissimilar materials — the aluminium window frame has a coefficient of thermal expansion of 23 x 10-6 per degree C while the concrete or brick masonry reveal has a coefficient of approximately 10 to 12 x 10-6 per degree C — the differential movement in a typical 1000 mm wide aluminium window over an Indian temperature range of 50 degrees C (5 degrees C winter minimum to 45 degrees C summer maximum at the facade surface) is approximately 0.65 mm. For a perimeter sealant joint of 6 to 8 mm width, this movement represents approximately 8 to 10 percent of joint width — within the movement capacity of both acrylic and silicone sealants. However, the actual joint movement at the aluminium-to-masonry interface is often larger than this theoretical calculation due to construction tolerances, structural frame deflection, and wind load on the window. Dr. Fixit Tileseal (silicone elastomer): Silicone sealants cure by moisture-cure chemistry to form a true rubber (silicone elastomer) with plus or minus 25 percent movement accommodation, permanent flexibility without hardening under UV, and long service life of 15 to 20 years in external joint applications. The critical limitation is that cured silicone cannot be painted — any paint applied over cured silicone will peel within months. Recommendation for external aluminium window frame sealing: For the interior face of the window frame (internal room side) where the joint will be painted to match the wall, use Dr. Fixit MP Sealant — it accommodates the movement, bonds to both aluminium and plaster, and accepts the interior emulsion paint. For the external face of the window frame (exterior facade side) where the joint may not be painted, or where the gap will be left exposed with a natural or coloured sealant finish, use Dr. Fixit Tileseal silicone for its superior movement accommodation, UV durability, and long service life. If the exterior joint must be painted to match the facade, use a primerless paintable silicone sealant (a specialty product) rather than standard MP Sealant, as this provides both paintability and silicone flexibility for external movement joints.