How To Correctly Build A Tile Shower Floor Pan

The most important part of the entire shower project to get right is absolutely the floor pan!

And, not surprisingly, this is where most do-it-yourselfers, make a mistake, try to make a shortcut, or just flat out get it wrong. Building the floor pan incorrectly can lead to leaking, of course, but also mold growth underneath the tile and mortar bed if a proper “pre-slope” isn’t installed. But, I don’t want to get ahead of myself, I’ll cover all the details how to do this later in the article. Let’s start here: What is a shower pan?

The term “pan” originates from when contractors used to install a copper pan in the base of where the shower was being built.

The “Before”:

The use of the copper pan transitioned into using 4 lb sheet lead (weighs 4lbs per sq ft, giving it that name), because it’s very malleable and could be shaped easily on site. A contractor could measure up the size needed, go out to the garage or driveway, bend up the corners as needed with a 2×6 and rubber mallet, folding corners over each other and overlapping so all the edges were at the top. Weighing 4lbs per square foot, it was quite a chunk to lug through the house, but could be done with two guys, and it could be folded in on itself, since it’s so malleable, in order to get through tight hallways and around corners.

Using the rubber mallet again, they would hammer an impression of the drain into the lead, giving a mark to cut out the drain hole. Once the hole was cut out, the drain flange could be attached, making a watertight seal. An adjustable shower drain was then threaded into the flange, and pea gravel placed around the weep holes to protect them from the deck mud that was installed next. Deck mud is a dry cement, wetted just enough to let the cement hold shape, allowing it to be packed in creating the slope needed for water to flow toward the drain.

The “Pre-Slope”:

Here is where many who take on the task of building their own shower, without any experience doing so, go wrong. The pre-slope is a slight slope of the floor draining toward the shower drain, created with dry-pack cement before the shower pan is installed. Despite what you may think, water can and will penetrate all the way through the tile, mortar and concrete above the shower pan, making its way down to the shower pan. In the absence of a pre-slope below the shower pan, the pan will be flat on the floor surface, keeping any of that water in the concrete from percolating down and into the weep holes of the shower drain. When the concrete remains moist, mold growth will occur over time, eventually causing considerable damage.

To create the pre-slope on a plywood surface you must first lay down a layer of felt paper (isolates concrete from floor movement), then staple down a layer of Metal Lath. Mix cement with enough water to get it to hold shape, and pack it down creating a slope from 1/8″ thick at the drain, up toward the shower edge at a slope of about 1/4″ per foot. On a concrete floor, the felt paper is not needed, concrete can be directly applied to floor.

Some point in between The “Before” and Now:

Labor time was greatly reduced when the use of vinyl membranes replaced the old lead pans. It can easily be rolled out, shaped into place in the shower, excess liner folded over itself in the corners, folded over the front shower curb, and a CPE bonding adhesive (in a can like PVC cement) used to seal up patches over corners. A newer kind of Tile Shower Drain was used with the vinyl membrane, like the one shown to the left.

The rubber membrane is to be wrapped up the wall NO LESS THAN 3 INCHES above the intended finished height of the shower threshold (curb or dam). Before wrapping the membrane up the sidewalls, install 2×10 board pieces between studs to give a solid support to the liner and places to nail the liner to the wall. No nails or other fasteners are to be used anywhere except along the top perimeter of the pan liner, in order to prevent eventual leaks from occurring at the nail holes.

After the pan liner is installed, metal lath can be wrapped around the shower curb, which is made of 3 2×4′s nailed one on top of the other creating a 4.5 inch high threshold, and cement packed into the lath and on top of it, shaping the concrete into a smooth squared off surface for tile to be applied to.

I always go an easier route, however, and use the Kirb-Perfect product made by Mark E Industries: a plastic a product easily assembled to form a cage around the lined shower threshold, instead of forming the metal lath.

Concrete board, 1/2″ thick 3′x5′ sheets, can then be measured, cut, and installed on walls using weatherproof screws (to keep rust stains from coming through grout later on as regular screws rust). The concrete board should be installed leaving a 1/2″ space between it and the pan liner, pressing the liner on the wall against the studs and 2×10 boards.

The Actual Concrete Slope:

Once the threshold is finished, create the concrete slope inside the shower pan liner, being careful to make the surface as smooth and even as possible to allow small floor tiles to lay better when tiling. A chalk line can be made around the concrete board on the walls for a guide line, giving about a 1/4″ – 1/2″ slope per foot up from the adjustable shower drain to the shower walls.

Again, I take the easier and quicker route, using Mark E’s Quick Pitch kit, which includes a plastic ring to place around the shower drain (protects weep holes from being filled by concrete), and slope plastic sticks that fit into the ring and are placed around it to radiate out to the corners and sides. They can easily be cut to length with tin snips or a saw. This gives me a perfect pitch every time, and fast!

Now: The Next System MOST People Will Transition To:

There is absolutely nothing wrong with the method I just explained to you. It is still used my the majority of contractors and, at this point, is the least expensive route to go. However, as you probably know, new technologies are coming along every year, revolutionizing ways things have been done in construction for decades and centuries.

A system I use now, when homeowners have a bigger budget, utilizes products made by a German brand named Schluter. They have competitors in their market, but they have led the way and own most of their market share. Their products all work together to make a completely waterproof shower, and can be installed much quicker than the old system just explained.

Schluter contends that even if your properly install a shower with the old system as I just described, water can still stay in the concrete for a prolonged amount of time causing mold problems. With their system, the floor and walls are waterproofed with a plastic membrane and there is no exposed concrete to absorb water below the tile. Water that goes through the tile will drain directly along the plastic membrane to the drain.

Here is how it works:

First, once plumbing and all else is ready, install concrete board to your walls, from floor to ceiling. I purchase Schluter’s Kerdi Shower-Kit that has almost all you need to build a waterproof shower ready for tile. The first item out of the kit to use is an expanded polystyrene shower base. It’s already built with the correct slope, all you need to do is cut the foam (quite easy to do) to fit the opening. Mix a batch of Thinset and apply with notched trowel to the subfloor, then set the shower base firmly into the mortar.

Next, you can set a Schluter Bench in place where desired, which is basically a big block of expanded polystyrene, and it too can be cut to fit the space quite easily. This is not included in the shower kit, so many times I still build my own bench with treated 2×4′s and concrete board.

In the shower kit is a product called Kerdi, a plastic sheet with bright orange fleece webbing adhered to both sides. The plastic membrane waterproofs the shower, and the webbing provides binding contact surface for ThinSet to adhere to on both sides; one side to the concrete board wall, and tile on the other side.

Apply the 3″ wide Kerdi Strips on all corners with ThinSet. After all corners are sealed, apply the Kerdi to the walls, and bench if you have one installed.

One Key Point About Applying Kerdi to Concrete Board Walls: Mix the ThinSet thinner than usual, pancake batter consistency, because otherwise the concrete board will suck the moisture out of the ThinSet before it ever sets up, and the Kerdi will peel right off!

Next, insert the included Shower Drain disc into a generous amount of ThinSet in the center hole and glue onto drain pipe below the floor. Then clean off excess ThinSet that oozed up through the holes around the ring of the disc.

Now install, with ThinSet, a piece of Kerdi on the floor, cutting out a hole for the drain. Then install the included Schluter Kerdi Shower Curb, cutting it to length, and setting with ThinSet. Again, this is easy to cut and install because it too is expanded polystyrene. Once it is set, install a piece of Kerdi up and over the shower curb, and seal corners with Kerdi-Kereck, also included in the shower kit. Also, at the openings around shower valves, install included Kerdi Seal pieces

Now you have the newest and best way to build a Shower Pan finished, and ready for tile!

… But we’ll save that for the next article! Get to work!