Kerdi tub surround-mortar on painted drywall

[jdkimes]

I'm doing a kerdi tub surround. Tiling tub up to ceiling.
The existing drywall only goes part way up. When I remove the existing tile I was going to leave the painted drywall above the tile.
Is it okay to put the mortar and kerdi over existing painted drywall if the paint and drywall are in good shape?
Down side is that I'll have partial butt joint in the drywall there. Maybe it's just as easy to remove it up to the ceiling.

[JTG]

Jeff
There is no problem with taking the existing tile off the wall and if easier take the wall board with it. When you use Kerdi you can put drywall back up. It doesn't need to be CBU. You also don't need to put Kerdi on all the way to the ceiling. I would only put it somewhere in the 5-6 foot range making sure that there is Kerdi over the wall board joints.
Good Luck
JTG

[jdkimes]

Thanks for the reply
I was think about just using the Kerdi part way up, but the amount that I'm buying from the Tile Experts is such that I might as well or else I'll have extra kerdi laying around in my garage for the next 5 yrs along with all the other extra home improvement supplies.

But either way I guess the question is: Is there a problem putting mortar (whether to lay tile or to put up kerdi) on a painted (assume latex) wall?
Do I need to do anything to the painted wall first like maybe some primer?