Does Backer Board Have to Be Replaced When Retiling a Bathroom?
Backerboard does not have to be replaced when you are retiling a bathroom floor. If you are able to remove the old tile without damaging the backerboard, you should be able to reuse it.
Minor Damage vs. Major Damage
If you only slightly damage the backerboard, use self-leveling compound to repair the minor damage. If the backerboard is severely damaged, you should replace it.