How Much of a Slope When Floating a Shower Floor?

Suitable Slope

• To force water to drain quickly out of the shower, the floor should slope toward the drain at a rate of at least 1/4 inch per foot of horizontal distance. In showers that are not perfectly square or where the drain is not centered, part of the floor may be steeper, as the required total rise is calculated using the distance between the floor drain and the wall farthest away from the drain.

Planning the Slope

• Thorough planning and detailed, careful measuring and marking will help to ensure proper drainage and minimize potential errors when placing the mortar. Use a measuring tape to determine the distance between the center of the drain and the wall farthest from the drain, marking the spot on the wall where the measurement was taken. Calculate the required rise. For example, if the wall is 30 inches from the drain and the desired slope is 1/4 inch per 12 inches, divide 30 by 12 and multiply this number by 1/4 to determine the total rise required. The floor will have to rise 5/8 inch between the drain and the wall. Measure and mark a point 5/8 inch above the original mark. Use a level to create a guideline on the wall around the entire shower perimeter.

Creating the Slope

• The mortar that must be built to have a slope is generally placed atop a metal lath that is stapled to a paper-covered subfloor. Use a trowel to pack the mortar into the lath and shape the mortar roughly to reflect the planned slope. Once there appears to be a fairly even surface between the drain and the line traced on the wall, place the level or a wooden board with an even edge with one end on the drain and the other on the line. Use the straight edge to identify and correct any low or high spots in the mortar with a trowel or float and finish the surface with the float.

Considerations

• In most cases, the slope is created in the layer of mortar that makes up the pre-pan, though some shower designs may only call for a single mortar layer. In shower pans that will have multiple mortar layers, only one layer must take slope into account and have varied thickness. Any other layers should have a uniform thickness so that the established slope is projected. Use a mortar according to manufacturer instructions or mix a thinset mortar to have a fairly dry consistency and consider adding a polymer additive to increase the strength of the mix.