How do you tank to a bath thats already in place?

any pics so we know what you mean

hi jay, basically, the bath is fitted into the bathroom already, simular to this pic:



I've been asked to re tile the room, they have an electric shower at 1 end of the bath, so want me to tank the walls around the bath. all the vids ive watchd on youtube are to do with tanking a wetroom, so not much help. I dont know what im supposed to do where the bath meets the wall.

with you now , might sound weird but this is one way mastic between bath and wall (this is for a membrane like laticrete Hydroban) then use masking tape to cover make sure its stuck .run the tape over the bath area apply membrane let dry then tile the masking tape covered in membrane should stick out past tile edge . grout then when dry use a Stanly knife to trim just under the tile edge before running a bead of silicone
hope you understand

arhhh its the mapei kit i shall be using.

I think i understand what you mean though. thanks jay