Wonderboard Or Hardie Board . The walls are going to be floated, but my tile guy wants to. However, you can only use hardibecaker indoors. How do you cut WonderBoard cement board? from truediy.net I know this has been discussed but i can't remember the consensus (if any) on whether to use wonderboard or hardibacker (both 1/2) over a plywood subfloor for a bathroom under thinset tile. This difference in materials affects their other properties. Durock can be used for both internal and external situations.