Guide
Shower pan vs pre-slope: what each layer does
People say "shower pan" for the whole floor of a tiled shower, but it is really a stack of layers. Knowing which is which helps you compare quotes and see who is responsible for what.
The layers, bottom to top
Subfloor or slab: the structure. It has to be solid, and a wood floor has to be stiff enough for tile.
Pre-slope: a mortar bed sloped toward the drain, built before any waterproofing. Its job is to make sure water that gets under the tile always runs to the drain instead of sitting flat.
Liner or membrane: the waterproof layer. In the traditional method it is a sheet liner over the pre-slope, clamped into the drain. In the newer method it is a sheet or liquid membrane bonded right under the tile.
Mortar bed: in the traditional method, a second dry pack bed over the liner, also sloped to the drain, which the tile is set on.
Tile and grout: the finish, set by the tile setter.
Two ways to build it
Traditional (water-in, water-out): pre-slope, then a liner, then a mortar bed on top. Water that soaks through the grout and the bed reaches the liner and drains through weep holes in the drain. The pre-slope is what keeps that water moving.
Bonded membrane: one sloped mortar bed, then a waterproofing membrane on top of it, then the tile. Water stops right under the tile. The bed underneath is the slope, so it has to be right.
Both are proven. The choice usually comes from the waterproofing system and the drain your tile setter or plumber uses.
How much slope
The usual rule is a quarter inch per foot (about 2 %) from the walls to the drain. Less, and water can pond; much more, and the floor feels steep under foot and large tiles will not follow it.
A point drain needs a bed that slopes in from all four sides, so the tiles have to be cut along the valleys. A linear drain needs the bed to slope one way only, which suits large tiles and curbless showers.
Who does what
The plumber sets the drain at the right height. The mortar-bed trade builds the pre-slope and the bed, and the curb if there is one. The waterproofer or the tile setter installs the liner or the membrane and tests it. The tile setter sets the tile.
On some jobs one company does several of these. Ask any quote which layers it includes, so nothing falls between two trades.
Questions
Do I need a pre-slope with a bonded membrane?
With a bonded membrane the single bed under it is the slope, so it has to be sloped to the drain. A separate pre-slope under a liner belongs to the traditional method.
Can a shower floor be flat?
No. Water has to run to the drain. Even a curbless shower floor slopes, usually a quarter inch per foot.
Does NewVision install the liner or membrane?
No. We build the pre-slope, the mortar bed and the curb, ready for your waterproofer or tile setter.