Method of making a pumpable, stable polydiorganosiloxane-silica foundation mixture and room temperature curing sealant

A process for making a pumpable, stable, polydiorganosiloxane-silica foundation mixture comprising

• (i) mixing a polydiorganosiloxane having a viscosity measured at 25.degree. C. of from 0.1 to 400 Pa.s, a diol surface modifying agent of the formula R'O(R.sub.2 SiO).sub.x R' wherein R is methyl, ethyl, vinyl, or 3,3,3-trifluoropropyl;
• each R' is selected from the group consisting of hydrogen atom, methyl radical, and ethyl radical;
• up to 30 percent of R' groups are methyl radical or ethyl radical, and x is a value of from 2 to 18 inclusive and the diol surface modifying agent has at least 3 weight percent silicon-bonded hydroxyl group, and reinforcing silica filler having a surface area of 90 to 500 m.sup.2 /g and making a Mixture 1 where the amount of the polydiorganosiloxane is from 50 to 100 weight percent of the amount necessary to provide from 80 to 95 weight percent in the foundation mixture, diol in an amount to provide from 20 to 100 weight percent of the amount necessary to provide from 0.05 to 0.5 part of diol per one part of silica filler in the foundation mixture, and silica filler in an amount to provide from 0 to 100 weight percent of the amount necessary to provide from 5 to 19.5 weight percent of silica filler in the foundation mixture based on the weight of the polydiorganosiloxane, the silica filler, and the diol being 100 weight percent, where the silica filler is dispersed throughout the polydiorganosiloxane
• (ii) mixing with Mixture 1, one or more increments, where an increment is at least 5 weight percent of the amount to be added, of diol and silica filler to make Mixture 2, where the amount of the diol is from 0 to 80 weight percent of the amount necessary to provide from 0.05 to 0.5 part of diol per one part of silica filler in the foundation mixture and the amount of the silica filler is up to 100 weight percent of the amount necessary to provide from 5 to 19.5 weight percent silica filler in the foundation mixture based on the weight of the polydiorganosiloxane, the silica filler, and the diol being 100 weight percent,
• (iii) mixing with Mixture 2, one or more increments, where an increment is at least 5 weight percent of the amount to be added, of polydiorganosiloxane as defined in (i) to make Mixture 3 and in an amount of 0 to 50 weight percent of the amount necessary to provide from 80 to 95 weight percent of the polydiorganosiloxane in the foundation mixture,
• (iv) mixing and heating Mixture 3 for at least 15 minutes at a temperature of from 50.degree. C. to 180.degree. C. while removing volatiles from Mixture 3, and obtaining a foundation mixture having from 5 to 19.5 weight percent silica filler and from 80 to 95 weight percent polydiorganosiloxane based on the weight of the polydiorganosiloxane, the silica filler, and the diol being 100 weight percent, where the foundation mixture has a plateau stress of >700 dynes/cm.sup.2 and a shear-thinned viscosity of no more than 1,000 Pa.s at a shear stress of 50,000 dynes/cm.sup.2 and the plateau stress and the shear-thinned viscosity are measured at 25.degree. C.