A method for protecting an electrical or electronic device against liquid damage, the method comprising a preliminary step of applying a continuous power plasma to the electrical or electronic device, followed by exposing the device to pulsed plasma comprising a compound of formula (I) where R1, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R4 is a group X—R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula C(O)O(CH2)nY where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group (O)pR6(O)q(CH2)t where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0, for a sufficient period of time to allow a polymeric layer to form on the surface of the electrical or electronic device. Devices protected by this method are protected from contamination by liquids, in particular environmental liquids.