Hi @Lawrence1,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Unfortunately, I don't think there is any waterproofing here at all. It looks like the tiles were stuck straight onto the plasterboard, which may have been painted, but not with a waterproofing membrane.
Is this tile in a location close to a shower, bath or sink?
If so, then the repair is not straightforward. It will likely require the bathroom to be gutted so the lining can be replaced, and a proper waterproofing membrane can be applied.
If the tile is not in an area that requires a waterproofing membrane, then you may be able to cut out the damaged plasterboard, replace it with some Aquachek™ Plasterboard and then reinstate the tile.
Let me know what you think and if you have further details or questions, please don't hesitate to add them to the discussion.
Jacob
