I will take the setting compound (recommended by the guy at Lowe's) back. Two more questions, I inadvertently put the hardibacker flush with the top of the tub. Hardi says to leave a 1/4 gap. Do I need to pull out the sheets and trim them?
Second, I built a two feet deep shelf / seat at the back of the tub, six inches up from the top of the tub. Since it will get minimal water and I sloped it slightly to drain into the tub, do I need to cover it with water resistant membrane such as kerdi? It is Hardibacker over plywood.
Thanks in advance for the help.