Provided is a method of applying a protective layer to an outer surfaced of a wind turbine rotor blade, which method includes the steps of preparing a protective layer for application to the outer surface of the rotor blade; providing an air exit channel between the rotor blade and the protective layer; attaching the protective layer to the outer surface of the rotor blade; and extracting air through the air exit channel. Further provided is a wind turbine rotor blade including a protective layer applied to an outer surface of the rotor blade using such a method.