A multiple glazed window unit employing a room temperature vulcanizable sealant is disclosed. The sealant comes in the form of two relatively low viscosity components, each of which has an unlimited storage life. When it is desired to apply the sealant, the components are fed to an extruder and blended together to form a cold flowable mastic material of relatively low viscosity which cures at room temperature to form a firm, tacky, resilient seal. Because each of the two components of the sealant composition are of low viscosity, the sealant can be extruded at relatively low temperatures, thus preventing rapid curing and insuring that the sealant composition will have an initial low viscosity, thereby permitting it to be applied to a multiple glazed unit with low temperature and pressure equipment.