How do I determine the size of waterproofing kit I might need?
Joints between the tray and rest of the floor and the walls is the most important part that needs to be sealed off 3 m2˛ of waterproofing kit is enough for that, should also last to cover the tray itself with it as well with 2 coats.
If you wanted to waterproof more space, maybe even entire floor, then you should go for 6 m2˛.
I will be happy to help if you have any questions.
David 020 7193 0953