This additive when used in specific Silicones, Inc. RTV-2 silicones, can create a non-flowing (thixotropic) version. It is recommended in situations where there is an extreme vertical surface, such as walls ornatural objects; for on-site architectural reproductions; and can enable cost effective glove molding of irregularly shaped items. The addition of SI-661 allows the silicone rubber to be applied with a brush, spatula or trowel. SI-661 can be used in GI-1000, GI-384, P-10, P-15, P-20, P-90 and P-45 (it is not recommended for other silicones) in amounts varying from 0.1 to 5% by weight, depending on the product. Mix the silicone rubber according to normal directions. After a homogeneous mixture is achieved, add the SI-661. If a skin (print) coat is desired, first apply the unmodified, catalyzed silicone rubber to the original, then immediately follow up with a layer (or layers) of the same silicone rubber containing the SI-661. Allow the silicone rubber to cure normally (usually 16 to 18 hours) before demolding.