Thanks guys, I wasn't expecting such rapid response.
Would you say it's essential for constructing a wetroom?
Should I do it myself or would it be worth paying a pro?
The practice ' back buttering' is essential when using Porcelain or Natural stone tiles in my opinion.
As Stef said, there will be a professional near you who will be able to price this wetroom for you.
We have a dedicated 'I am looking for a Wall & Floor Tiler' section for this purpose.