Smooth-Sil™ 936 vs RTV-4135 Silicone Comparison

Smooth-Sil™ 936 and RTV-4135 are both platinum-cure RTV-2 silicones for mold making and casting, with closely matched hardness at 36 Shore A and 35±1 Shore A respectively. This comparison examines their published technical specifications, processing characteristics and mechanical properties to help manufacturers evaluate RTV-4135 as a potential alternative.

Smooth-Sil™ 936 and RTV-4135 have closely matched hardness at 36 Shore A and 35±1 Shore A respectively. Both provide a relatively firm mold profile for applications where more body and dimensional stability are needed than softer silicone grades.

One of the clearest differences is the mixing system. Smooth-Sil™ 936 uses a 100A:10B ratio by weight, while RTV-4135 uses a 1:1 ratio by weight or volume. The 1:1 system can simplify routine batch preparation, while the 100A:10B system requires more precise weighing.

Working and cure times also differ significantly. Smooth-Sil™ 936 has a published 60-minute pot life and approximately 24-hour cure time, while RTV-4135 has a 30–40-minute working time and approximately 4–5-hour cure time. Smooth-Sil™ 936 therefore provides a longer working window, while RTV-4135 offers a substantially shorter published cure cycle.

Viscosity should be interpreted carefully. Smooth-Sil™ 936 is listed at 21,000 cps, while MinghuiLink reports approximately 4,500 mPa·s for Part A of RTV-4135. Because the manufacturers report viscosity at different measurement points, these figures should not be treated as a direct like-for-like comparison. Actual flow, air release and detail reproduction should be evaluated with the intended mold geometry.

The published mechanical data also show different performance profiles. RTV-4135 reports higher published tensile and tear strength, while Smooth-Sil™ 936 reports higher elongation. Because the manufacturers may use different test methods and conditions, these figures should be treated as reference data rather than a strict laboratory ranking.