This invention provides a method of sealing and purging contaminants from the internal free spaces of an insulated electrical device by forcing into said free spaces a low viscosity material that acts to displace fluid contaminants from within said free spaces. The material later cures in situ to form a hydrophobic seal with good electrical properties. Also disclosed herein is a method for rehabilitating waterlogged plastic insulated multiconductor communications cables of the type employed in telephone systems.