An apparatus for working a wet coating, such as render material, applied to a surface, the apparatus comprising: an actuator arranged to move an arm across a surface having a wet coating applied thereon; a controller configured to move the arm across the surface along a tool path; and a tool head mounted to the arm, the tool head comprising a compliance module and a tool mounted to the compliance module such that the tool is movable in a stroke direction towards the surface relative to the arm. The compliance module comprises a biasing module arranged to urge the tool in the stroke direction to maintain contact between the tool and the wet coating such that the tool works the wet coating as the arm moves across the surface.