Yep....I agree with Pete.
Depending on the age of the house, there have been two "accepted" systems in wet areas. ie. Shower recesses etc.
Going back maybe 20 years the accepted system (still in use by older plumbers) was to install a copper tray over the floor into which the waste flange was brazed. The sides of the tray would extend up the wall studs by about 20cm (8") and all joins were brazed making a totally water proof well.
Some plumbers tried to save by using a galvanised sheet but found it rusted out after about 10 years leading to leaks.
The shower wall lining (usually a hardie sheet) was then installed extending down into the tray to just off the bottom. A concrete base about 5 - 7.5cm (2"- 3") was then poured into the tray as a base for the tiles.
A 90 degree flashing was used behind the wall lining at the corner join which also extended down into the tray.
All of that was then dressed up by the tiles but note....the tiles were not to provide water proofness. Done properly, a shower recess is water proof without any tiles.
Advances in sythetic rubbers and urethanes lead to the system Pete refers to in which the tray is replaced by an applied sealer ( quite thick application and using a fabric reinforcement over a cement based sheet). Usually however this system is for use on slab floors. The tray system is still the preferred over a timber floor.
How do I know you ask?
, Cus I had to replace a bathroom and ensuite in this place at no small expense. The first wife goes right Pi$$ed off when carpets in adjoining rooms were getting soaked after a shower.
First Class PITW ( pain in the wallet)