Two-part, ultra low modulus silicone sealant

A two-part composition which is stable on storage as two parts and curable at room temperature, upon mixing of an equal weight of the two parts, to yield a silicone elastomer, the composition consisting essentially of

• Part 1, consisting essentially of the product obtained by mixing under anhydrous conditions
• (A) 100 parts by weight of a hydroxyl radical endblocked polydiorganosiloxane having a viscosity at 25.degree. C. of from 5 to 100 Pa.s and in which the organic groups are selected from the group consisting of methyl, ethyl, vinyl, phenyl, and 3,3,3-trifluoropropyl radicals, in said polydiorganosiloxane no more than 50 percent of the organic groups being phenyl or 3,3,3-trifluoropropyl radicals and no more than 10 percent of the organic groups being vinyl radicals,
• (B) from 25 to 150 parts by weight of non-acidic, non reinforcing filler having an average particle size of from 1 to 8 micrometers,
• (C) from 2.5 to 10 parts by weight of a silane of the general formula ##STR5## in which R' is an organic radical selected from the group consisting of methyl, ethyl, and phenyl, said silane being present in an amount sufficient to provide at least one silane molecule per hydroxyl radical of the polydiorganosiloxane,
• (D) from 1 to 6 parts by weight of an aminoxysilicone compound having from 1 to 100 silicon atoms per molecule and from 3 to 10 aminoxy groups per molecule, said aminoxy group having a general formula --OX in which X is a monovalent amine radical selected from the group consisting of --NR.sub.2 and a heterocyclic amine, R is a monovalent hydrocarbon radical, the --OX group being bonded to silicon through the SiO bond, the remaining valences of the silicon atoms in the aminoxysilicone compound being satisfied by divalent oxygen atoms which link the silicon atoms of the aminoxysilicone compounds having two or more silicon atoms per molecule through silicon-oxygen-silicon bonds and by monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals bonded to the silicon atoms through silicon-carbon bonds, there being an average of at least one monovalent hydrocarbon radical or halogenated monovalent hydrocarbon radical per silicon atom,
• (E) from 0 to 20 percent by weight of the combination of part 1 and part 2 of a diluent consisting of non-reactive silicone fluid having a viscosity of from 1 to 100 Pa.s at 20.degree. C., and Part 2, consisting essentially of the product obtained by mixing
• (F) 100 parts by weight of (A),
• (G) from 25 to 150 parts by weight of (B),
• (H) from 0 to 20 percent of the weight of the combination of part 1 and part 2 of (E), and
• (I) from 0.2 to 4 parts by weight of water, and when equal weights of part 1 and part 2 are combined said silane (C) and said aminoxysilicone compound (D) being present in amounts sufficient to provide a combined weight of at least 5 parts by weight per 100 parts by weight of (A), and said aminoxysilicone compound (D) being present in an amount which is not greater than the weight of silane (C), said composition curing to a non-flowing gel in less than 3 hours at a temperature of 25.degree. C.