High voltage insulators

A method of manufacturing an improved electrical high voltage coated insulator is described. The method involves applying and curing a one-part, room temperature curable silicone composition to the surface of an insulator, the insulator surface having a minimum designated arc resistance. The silicone composition is the product obtained by mixing in the substantial absence of moisture a specified polydimethylsiloxane fluid containing hydroxyl radicals, finely divided aluminium hydroxide filler, a silane of the formula RbSi(ON=X)4-b and an optional condensation catalyst. The composition cures on exposure to atmospheric moisture to produce a coating on the insulator that resists the development of leakage currents and flashover failure upon exposure to electrical stress, moisture, contamination, and other outdoor weathering stresses.