Apparatus for treating a surface of a wind turbine blade (14), comprising an expandable structure (22) that is deployable from a collapsed state into an expanded state in which the structure defines an elongated treatment zone (32) into which a blade (14) is receivable in use. The apparatus includes treating means (52) arranged to apply a treatment in the treatment zone. Also provided is a method for treating a wind turbine blade (14) including: positioning a wind turbine blade in a substantially vertical orientation; locating an expandable structure (22) adjacent the wind turbine blade; deploying the expandable structure (22) about the blade (14) such that the expandable structure (22) defines an elongated treatment zone (32) which receives at least part of the blade (14); and applying surface treatment to the surface of the blade (14) using the expandable structure (22).