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Abstract

The specification describes and claims curable polysiloxane compositions filled with a mixture of two types of finely divided calcium carbonate. The curable polysiloxane comprises 100 parts by weight of a hydroxypolysiloxane with from 5 to 12 parts by weight of a curing agent therefore comprising a silane of the formula R.sub.a R'.sub.b Si or a siloxane having units ##EQU1## wherein each R represents a monovalent hydrocarbon group, each R' represents an hydroxy, alkoxy, or alkoxyalkoxy group, a+b=4, a has a value 0 or 1, b has a value 3 or 4, c has a value 1, 2 or 3 and a+c is not greater than 3 as exemplified by methyl trimethoxy silane, together with a catalytic amount of a titanium or tin compound for promoting curing of the product in presence of moisture of the atmosphere. The composition contains, per 100 parts by weight of the polysiloxane, from 50 to 200 parts by weight of a filler comprising a mixture of 10 to 80% by weight of the mixture of a calcium carbonate composed principally of particles having a surface area from 10 m.sup.2 /g to 30 m.sup.2 /g and 20 to 90% by weight of the mixture of a calcium carbonate composed principally of particles having a surface area from 0.5 m.sup.2 /g to 12 m.sup.2 /g. The compositions are applicable as sealant compositions having a desirable blend of properties including adhesion to various surfaces.

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First Claim