Change of plane grout advice

[Bonesteel]

Hello, I am in the middle of my first mud bed shower install for my mother, and she would very much prefer grout instead of caulk where the floor meets the walls. I have done several surrounds with grout at vertical corners and had no issues, but I am concerned with the floor seam.
So far I have completed the preslope and am currently insyalling blocking for the shower pan, seat, and grab bar.
My question is, is there any steps I can take at this point to increase my chances of grout survival, I was thinking maybe lath on the concrete board just to the height of the final mudbed, but am open to any other ideas.
I am aware that caulk is the "right" solution for changes of plane, but am going to give grout a go first regardless, just looking to minimize chances of having to dig it all out and replace with caulk.
Also any brand of grout that would be recommended as well as a source for it. I have always just used polyblend in the past, but paroosing this site it seems that is not likely the best solution.
Thanks a ton in advance,
Chris.

[Davy]

Chris, like you said, caulk or silicone is what's recommended and what most use. I mud my walls so I use grout in all my joints except where tile meets the bath tub. In a shower, I use grout everywhere and 99% of the time I have no cracking grout anywhere. But, the mud walls play a part in that. You can go ahead and use grout and just rake it out if it ever cracks and add more grout. It might crack out every few years or who knows, it may never crack, no one knows. I will say that if you have any foundation issues, it's especially good to have the silicone for movement. With grout in the corners, the movement is more likely to crack tiles.

I never had a lot of problems with Polyblend but others have. I pretty much have gone to using Prism grout instead. It's made by Customs and seems to get much harder than Polyblend. Also the color is more consistent with Prism.

I don't know of any steps you can take other than to anchor all the blocking well to try to reduce movement.

[Kman]

If you use a membrane at the corners (something like Kerdi band) under the tile, that can help absorb some movement. There's no guarantees, though.

[jadnashua]

If you want to avoid caulk, but might consider an engineered flexible joint that never should need to be replaced, Schluter has a good selection. A couple of other companies also make some, but Schluter has the largest selection that I've fond.

[Bonesteel]

Its not that I want to avoid caulk, as much as it is that I want to use grout for uniform appearance, so the engineered joints wont work for me.
I was thinking maybe something like kerdi band to tie the mud bed to the concrete board, or possibly bent lath or just fiberglass tape, just curious as to whether or not others have a clever solution or something they frequently use, I have seen many say that they use grout instead of caulk

[jadnashua]

Sometimes you get lucky. The industry standards are designed so you don't have to be.

Things in a building expand and contract with variations in temperature and often, humidity levels. Things do not expand and contract at the same rates. There are limits on the amount of microscopic bending cement based products can handle...when you exceed that, things break down. STresses are concentrated in corners and changes of plain.

So, it depends...do you feel lucky? ARe you willing to redo it if you aren't?

Sometimes, things can look good for a long time, then all of the stars align, or maybe go into disarray, depending on your point of view, and then fail.

[jwmezzanotte]

Can anyone share an example of any type of failure caused specifically by grouting the pan-wall joint?

[Just In Tile LLC]

I'm with Davy, grout my joints on mudwork except againsts tubs or prefab pans. As far as specifics in the building process now to help with that I wouldn't know. Mud it being your best bet.

Most systems now are all panels, with joints that are taped and not really monolithic or have the overall mass as mud so they are more apt to move with the structure as separate units instead of as whole. If I was going to have a go at what you're doing, anything that secures the space you're tiling more would help. And.... in a perfect world isolates it from the rest of the structure outside the shower. (Not gonna happen with how we build things)

[cx]

John, cracked grout is considered a tile installation failure and what you're most likely to see when you grout the wall/floor joint in a shower.

And that particular joint is no more monolithic in a traditionally built mud wall shower than in a traditionally built receptor with CBU walls.

That said, I've always grouted those joints in all my showers of whatever construction.

My opinion; worth price charged.