The black sheetrock screws DO rust, though they won't if you completely
encapsulate them (that would mean from all sides). If you're concerned,
you can use galvanized or stainless decking screws.

peter wrote:

Has anyone ever used drywall screws (the black ones for screwing
plasterboard - I think you call it sheetrock in the US- onto metal
studs and plastering over) for holding the strips in the right
alignment, instead of wooden dowels and/or plywood cleats, or is it a
really dumb idea? I mean just for those annoying bits where the new
strip won't quite line up over the one in place.

The screws don't rust as far as I know and as the whole lot is
encapsulated in epoxy afterwards I doubt if they ever would. I've used
them for fixing things into wood for years and never noticed any
detrimental effect, so I doubt that they would cause an damage to the
wood, assuming a pilot hole was drilled first.

It's just that they are so cheap and are so easy and quick to screw
in.

Another Pete