When I use the cardboard cake boards to put a cake on, I'll get grease marks from the BC icing. How can I avoid this from happening? Or should I just cover it up with piping?
If I cover the board in fondant and then put the frosted cake on top of that, would there be grease marks in the fondant?
Cover the board with greaseproof paper. There are lots of choices - Wilton's FanciFoil; freezer wrap; wrapping papers that are foil; commercially made doilies; Contac Paper or fondant.
Agree .... cover with paper or buy the wax coated boards.