Green/Cement Board Overlapping Tub Flange vs Leaving Gap Between Board and Flange
It looks like this subject has been beaten to death on the internet but there doesn't seem to be a consensus, so I thought I'd ask you guys which is better. I'm looking at using Swanstone tub walls with a Kohler tub.
The Kohler tub instructions say to use furring strips to provide a flat surface for the wallboard to overlap the tub flange:
Attachment 17364Attachment 17365
But the Swanstone wall instructions say to stop short of the tub flange:
The second method, leaving a gap, seems the simplest since you wouldn't need a 1/4" thickness transition with the rest of the bathroom walls. Is there any reason to choose one method over the other, or does it not really matter?
LEaving a gap between GreenEBoard and tub tile flange
The top diagram is how the walls should be built to TCNA specifications. That said most times builders and home owners do not like the overlap.
When you overlap you are forced to use a thinner backer board or build the wall out thicker.
Personally I have been loving the use of Noble or Kerdi at this weak point.
Step one is to make sure the plastic film is removed and to protect the tub from harm.
There should be a gap between the tub's flange top and the Green EBoard or concrete board.
Sealing the gap between cement board and tub deck
This tub surround got Noble Seal TS and then Aqua Defence.
Once the gap has been checked, the tub protected from harm the next step is to use some thin-set on the backer board and some Kerdi Fix over the tub's tile flange. Don't mix these products. First the thin-set - then the Kerdi fix!
Do not fill the gap between the two, if some thin-set fills this space comb it out with a scrap of cardboard or a coffee stir stick.