A method of masking part of a surface of a wall of a combustor shell, the surface including at least one area having a plurality of cooling holes defined therein, the method comprising: applying a viscous curable masking compound to the part of the surface over an entirety of each of the at least one area, including blocking access to the plurality of cooling holes from the surface by applying the masking compound over the plurality of cooling holes without completely filling the plurality of cooling holes with the masking compound; and forming a respective solid masking element completely covering each of the at least one area and the plurality of cooling holes defined therein by curing the masking compound; characterised in that: applying the masking compound over the entirety of each of the at least one area includes relatively displacing the component and a nozzle of an automated dispensing tool while maintaining a predetermined relative distance (h) between a dispensing tip of the nozzle at a predetermined distance (h) from the surface as it is moved across a width (w) of the area until the at least one area is completely covered, and expelling the masking compound from the tip of the nozzle onto the area; a position and/or profile of the surface is measured before or as the masking compound is applied to be able to maintain the dispensing tip at the predetermined distance, the nozzle being mounted on a robotic machine programmable to follow a geometry of the shell; applying the viscous material continuously over the plurality of cooling holes is performed such that the masking compound penetrates in each hole along a distance corresponding to less than half of a depth of the hole and/or less than a diameter of the hole; and the masking compound has a viscosity of at least 15000 cP.. applying a viscous curable masking compound to the part of the surface over an entirety of each of the at least one area, including blocking access to the plurality of cooling holes from the surface by applying the masking compound over the plurality of cooling holes without completely filling the plurality of cooling holes with the masking compound; and forming a respective solid masking element completely covering each of the at least one area and the plurality of cooling holes defined therein by curing the masking compound; characterised in that: applying the masking compound over the entirety of each of the at least one area includes relatively displacing the component and a nozzle of an automated dispensing tool while maintaining a predetermined relative distance (h) between a dispensing tip of the nozzle at a predetermined distance (h) from the surface as it is moved across a width (w) of the area until the at least one area is completely covered, and expelling the masking compound from the tip of the nozzle onto the area; a position and/or profile of the surface is measured before or as the masking compound is applied to be able to maintain the dispensing tip at the predetermined distance, the nozzle being mounted on a robotic machine programmable to follow a geometry of the shell; applying the viscous material continuously over the plurality of cooling holes is performed such that the masking compound penetrates in each hole along a distance corresponding to less than half of a depth of the hole and/or less than a diameter of the hole; and the masking compound has a viscosity of at least 15000 cP.. applying the masking compound over the entirety of each of the at least one area includes relatively displacing the component and a nozzle of an automated dispensing tool while maintaining a predetermined relative distance (h) between a dispensing tip of the nozzle at a predetermined distance (h) from the surface as it is moved across a width (w) of the area until the at least one area is completely covered, and expelling the masking compound from the tip of the nozzle onto the area; a position and/or profile of the surface is measured before or as the masking compound is applied to be able to maintain the dispensing tip at the predetermined distance, the nozzle being mounted on a robotic machine programmable to follow a geometry of the shell; applying the viscous material continuously over the plurality of cooling holes is performed such that the masking compound penetrates in each hole along a distance corresponding to less than half of a depth of the hole and/or less than a diameter of the hole; and the masking compound has a viscosity of at least 15000 cP..