II am installing a marble floor,I am going to lay down wonderboard over a hardwood floor.Does it have to be glued down before I screw it down?

I would strongly recommend to remove the hardwood before installing tile.

Your floor will most likely fail if you install backerboard over the existing hardwood.

It's better to remove it and eliminate any problems that could occur. Rather than re-doing the job completely.

"Get it Done Right the First Time!"

Matt
tile contractor
Charlotte, NC