Most people would tank the area first but BAL seem to say that their White Star doesn't need it.
"A white, highly flexible, water resistant, non-slip, ready mixed ceramic wall tile adhesive designed for use in internal wet and dry areas. It can be used for domestic or commercial applications such as communal showers. Use on a variety of backgrounds including, plasterboard, plaster, cement: sand rendering, existing ceramic tiles, paint, tile backboards, worktops and wooden backgrounds."
Maybe give them a call to see what they say?
Oh and yes, you tile the bit you would skim, the side with no writing on it.