Does Shower Pan Need A Pre-Slope? (Explained!)

A shower pan can be a beautiful element in the bathroom, especially when it blends perfectly with its environment’s tiles and other elements. The beauty, though, will be short-lived if the standard shower pan installation procedures and best practices for the installation are not followed. Following the standard shower pan installation procedure means you have to understand if your shower pan needs pre-slope or not.

The pre-slope sits on the subfloor and is the foundation to shower pan moisture management. The pre-slope sets the standard negative slope on which every other layer will sit. It directs the water from the shower walls and floors to the shower drain and deters water from pooling in any shower pan area.

Failure to install the pre-slope could be the difference between having water damage and mildew in your shower. The possibilities that water would go through your mortar bed under the tiled shower floor are higher. Therefore, to prevent the water that goes through your liner from reaching your sub-floor or cement floor, you must consider installing a pre-slope before installing your shower pan. 

Here’s if shower pan need a pre slope:

Pre-slopes are necessary for shower pans because it helps direct excess water into the drain area, so there is a constant movement of water that doesn’t damage the mud bed. If the underneath liner is flat, escaping water can build up and form mold and other goodies. However, pre-slope helps avoid damage to the mud bed. 

Do you need to pre-slope a shower pan?

The function of a shower slope in a shower pan is to direct all water towards the drain. The pre-slope is often under the tile and thin-set and created with a mortar. The pre-slope creates a base for you to lay your tiles.

The pre-slope sits on the subfloor and helps control shower pan moisture. A perfectly installed pre-slope could help avoid dampness, mold, and other frustrating development in the future. Suppose the underneath liner is flat – without a pre-slope to the drain. In that case, you may start to experience water build-up, and the mud in the shower pan will get saturated within the first few weeks of use.

With constant usage, water will get into the mud bed via the sanded grout causing water build-up eventually causing mildew. This is the type of water damage you wouldn’t have to deal with if you install a pre-slope because the pre-slope would have helped set the proper negative slope that your shower pan will sit on to deter water from pooling in any area of the shower pan.

How much slope does a shower pan need?

A shower pan needs at least a 4 percent slope for a shower floor for effective draining. This means a 1/2-inch drop per every 12 inches from the walls to the drain. Traditionally, the slopes for a bathroom tile construction are established in the mortar pre-pan.

What is the minimum slope for a shower floor?

Usually, the minimum slope recommendation for tile shower construction is two percent, or 1/4 inch per foot. For example, the grade of a location four feet away from your house should be one inch lesser than the grade next to your house. This is perfect for most locations with water-absorbing soil.

How to calculate the slope of a shower 

The first step to calculating the slope of a shower is to measure from the drain opening to the wall and round up the calculation to the nearest foot, then multiply your measurement by 1/4 inch. For example, if the drain opening measures 2-foot 8-inches from the wall, that means the shower floor should slope 3/4 inch from the shower walls to the water drain.

How do I level a floor for a shower pan? 

Place the leveler on the top edge of the pan to check for level. Then put the shims under the shower pan in the corresponding areas for shimmed installations. The shims are held tight by the pan’s weight while the shower pan is screwed on the wall studs through its flanges. 

What do you use to pre-slope a shower?

The ideal material used to pre-slope a shower is a mortar (standard cement mix with sand and Portland cement.) The mortar should be strong and rich enough to create a great water-resistant barrier and support the weight of the shower pan and the users.

What type of mortar do you use for a shower pan? 

The standard mortar for a shower pan is a combination of cement mix with sand and Portland cement. A well-constructed mortar supports the weight of the shower unit and creates a great water-resistance barrier that would help the shower pan last longer.   

How thick should the pre-slope be? 

For proper drainage, the pre-slope shower pan thickness should be ¼ inch in height for every 12 inches of run travel from the shower drain center. In addition, the mortar thickness in the pre-slope should be ½” to 1″ thick.

How long does a pre-slope take to dry? 

It takes an average of twenty-four hours for a pre-slope to get dried. However, if the liner idents the mud, then you may have to re-evaluate and give it more time to dry up.

How many falls should a shower have?

The floor is supposed to fall from the bathroom floors. The recommended minimum fall to the drainage should be 1:100 (10mm per 1m). In bathrooms with a vertical separation between the shower area and the wet area, like the hob, shower screen, set-down, or water stop, the recommended fall to the drainage is 1:100.


A pre-slope is one of the most integral steps in a shower pan installation. The pre-slope helps water get into the drainage hole and helps prevent mold, dampness, and other frustrating development in the future that could damage the mortar. It is important to note that you can install your shower pan without a pre-slope.

However, a shower pan without a pre-slope leaves your mortar vulnerable over time. The mortar in your shower pan will get saturated and eventually weaken the subfloor. Save yourself the headache and time to repair or start the whole flooring process again in the future by adding a pre-slope installation plan to your bathroom plans today.