This is in a house my wife bought to refurbish as an investment. She had her brother "managing" the project and he hired a muppet builder who caused more work that needs to be put right. My brother in law has been fired and I am now in charge of all the fixing. After more research, I anticipated needing to buy a tanking kit and ordered one last nght. If I receive convincing advise, I will replace the standard drywall with greenboard and tank the shower area. What do you think - greenboard?