Hi Stefan!

@You : "...Looked up the 3DCoat site on how to mask (flat) areas of a surface...@


I'm not sure I understand well, but there are in 3DCoat at least a couple of main tools that you can use to "mask" areas :

1) "Vox Hide" in Voxel Mode

2) "Freeze" in Surface Mode

Both tools work in tandem with the "Freeze" and "Geometry" menu :






You can use these commands to perform very sophisticated editing of voxels/surfaces

Here's a very basic and rough example on how to use the "Freeze" tool to "mask" flat areas.
The key is to switch from perspective to "orthographic" view.

The video : http://take.ms/sULSP



But I don't know if I understood your question correctly :)

Let me know.

Ciao!

Marco (mkdm)