QUESTION

I hired a tile guy to float a few shower stalls with mud. The building is old, but solid, It has a overbuilt foundation from 2 years ago and any framing changes in the substrate were solid 2x6 16 oc. Everything really solid. He claims the cracks and inward bowing in all 3 showers are due to movement in the building. Considering we tore out a 15 year old shower without cracks in it, I have trouble believing any of that. He used aqua 'b' paper (something like that) Stapled every 5 or so inches with lathe - floated with Type S mortar about 3/4 " thick and used a Versabond polymer modified grout approx 1/8 to 1/4 thick. Tile is 3x6 ceramic subway. Walls bowed as much as 1/8" over 3 feet - mostly at the bottom 1/3rd of the wall. Cracks are hairline at the edges of the bows. Bows sit off the sheetrock. One of the showers had a thicker ceramic band of tile and the bows were minimal on this shower. Other than that, the showers are on the same aspect of the building, share similar walls and all share one exterior wall. We tore out one of the showers and the mortar appears brittle - some pieces I can break up with 2 hands. Any thoughts are appreciated!!!

ANSWER

ANSWER -  First of all, tile applications installed on shower walls should not bow or crack.   What you describe sounds like it is a shrinkage problem in the floated wall mortar bed.  You didn't mention whether the installer installed a scratch coat over the metal lath, so I will assume he installed a one coat 3/4" thick mortar bed on the walls.   I assume the Versabond is a thin-set mortar adhesive and not a grout for the grout joints.

This type of application in a shower should not have regular gypsum sheetrock sheathing installed over the studs.  Per TCNA B440.15 it should be a coated glass mat or fiber-reinforced water-resistant gypsum board or a cement backer board.

The shrinkage could have been caused because the installer didn't properly fasten the metal lath down.  And/or it could be the mortar mix was too rich (too high ratio of cement to sand).  And/or the mortar mix had too much water in it.   These deficiencies would have to be confirmed and there could be other compounding deficiencies that have contributed to the failure.  This would require a forensic inspection/investigation, which may or may not be practical for your situation.