I agree. For a shower a more resistant substrate is a necessity, but for a powder room wall, drywall is more than adequate.

This is much akin to a lot of questions we get at the John Bridge Forum about installing Kerdi membrane in showers over drywall....yes, drywall in a shower!

Much like the paper facing issue brought up here, Kerdi is applied over drywall with thinset. We've had a number of posters complaining that, the next day, it's easy to peel a corner away from the drywall. Again, try pulling DOWN on the Kerdi from the bottom edge....can't be done, and that's why the tile isn't gonna fall off.

Same applies to tile over drywall....particularly on a "dry" wall install.

I have tile wainscots applied directly over drywall. Been there for 15 years, not going anywhere.

Thanks for the responses. I'm so glad to hear this!

What else did this 'salesman' tell you ?

My most recent "bad salesperson advice" was to make sure I got unsanded grout for the glass tile I had loaded onto a cart. I gave her a quizzical look, and pointed out that the tile was ceramic, not glass. She said she was referring to the shiny finish, and warned me that sanded grout would scratch it.

I refrained from pointing out that the bag of sanded grout said "for porcelain, ceramic, and glass tile....." and just went on my way.

In a dry area, such as the one being discussed, there is no need for Kerdi over the drywall. Tiling directly over the drywall is very acceptable.

Bill, didn't mean to imply Kerdi was needed here. Just making the comparison of sheer vs lateral strength.

Can you clarify, if tiling up to the ceiling above a soaking tub (without a handheld shower head), can you tile over established drywall that has Kerdi applied over the drywall. Or is cement board better? I had also thought you cannot tile over drywall.

"... if tiling up to the ceiling above a soaking tub (without a handheld
shower head), can you tile over established drywall that has Kerdi
applied over the drywall."

For the walls around a soaking tub, if you want to hang Kerdi on the drywall and tile on the Kerdi, that's perfectly acceptable.

"I had also thought you cannot tile over drywall."

In non-wet areas, you can tile directly on drywall. Example, bathroom walls outside of the shower, or kitchen back splashes.

You can't tile directly on gypsum board in wet areas like
showers and tub surrounds, even if the gypsum board is moisture resistant.

In a wet area, Schluter allows
Kerdi to be installed over gypsum board. In that case, the tile is on
the Kerdi, and the Kerdi is protecting the gypsum board.

Thank you MongoCT

There is excellent advice here, but the one thing I haven't seen is any mention of the flatness of the existing drywall. As you move to larger tiles, lippage can be a problem in any circumstances, but particularly with walls that are finished in sheetrock as they can be subtly bowed without it being apparent. Just to make sure the walls are relatively flat before tiling, it would be a good idea to check with a 4'-6' level, or a perfectly straight piece of lumber.

Kudzu....I have a question relating to flatness of drywall.

I'm having subway tile installed as a kitchen backsplash in two weeks, along with marble mosaic on mesh behind the stove.

I do remember when the cabinets were installed that our walls were bowed....not to the eye of course.

What kind of issues will we have for the backsplash install? I suppose I need to let the installer know beforehand?

Depends on the amount of "bowing."

I know it's only on the wall to the left of sink, so I'll ask dh and see how much.

Your installer should check for wall flatness with a true straight edge, like a 4'-6' level. A good installer can compensate for some bowing by varying the thickness of the thinset a bit. The main issues are always:

-Is my wall/floor flat?

-Are my tiles flat?

-What size are my tiles? (Smaller tiles are less prone to lippage.)

-Is the tile layout pattern I've chosen -- offset or not -- going to cause issues if the tiles or tiling surfaces aren't flat?

Even smaller tiles, like subway tiles, can have problems if things aren't optimal.

You can look at these other posts to see what kinds of issues people have had (some of the posts have pictures) : Lippage

This is very helpful.

Thank you, kudzu.