Tile work that starts with the waterproofing.

Tile and grout are not waterproof: cement grout is porous by design, water moves through it, and the assembly behind it is supposed to handle that. When a shower leaks, the tile is almost always intact, and the failure is at a corner, a curb, a drain connection or a change of plane in the layer underneath.

The current standard is a bonded waterproof membrane, a sheet like Schluter-Kerdi, a foam board panel with sealed seams, or a liquid membrane rolled on in two coats, connected to a bonding-flange drain so the waterproof plane and the drain are one system. The older mud bed over a PVC liner still works when there is a pre-slope under the liner; built flat, which is common, the liner holds standing water inside the wall, and a musty twenty-year-old shower with no visible leak is usually exactly that.

Cement backer board is dimensionally stable and unaffected by water, and it is not waterproof: water passes straight through it, so in a wet area it is a substrate for a membrane, not a substitute for one. Foam panels like Kerdi-Board are waterproof in themselves and usually the better buy on a shower with a bench, a niche and a curb, because the tricky geometry is where a sheet membrane takes the longest.

On floors, an uncoupling membrane like Schluter-Ditra separates the tile from a wood-framed subfloor that deflects and moves seasonally, which is where hairline cracks running through tiles in a straight line come from. If the joists are undersized or overspanned for tile, we say so before setting anything, because no membrane fixes a bouncy floor.

Large-format tile shows every substrate variation as lippage, so it gets a flattened substrate, back-buttering with the right notch trowel, leveling clips while the mortar cures, and a third-offset running bond, which most large-format manufacturers now specify. Layout gets decided before the first tile: full tiles at the entry and the focal wall, sliver cuts eliminated, the niche sized to whole tiles, and every change of plane, inside corners and tile to tub, finished with flexible sealant rather than grout, because grout in a moving joint cracks.

Electric floor heat goes in while the floor is already open, with the sensor probe run between cable loops so a failure can be pulled and replaced, the dedicated circuit on the electrician's list before the walls close, and resistance readings taken before, during and after the set. Products like Ditra-Heat combine the uncoupling membrane and the heat cable in one layer.