How to Properly Build a Tile Shower Floor Tray

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

And, unsurprisingly, this is where most DIYers make a mistake, try to make a shortcut, or just mess up. Improper floor pan construction can lead to leaks, of course, but also mold growth under the tile and mortar layer if proper “pre-pitch” is not installed. But, I don’t want to get ahead of myself, I’ll cover all the details on how to do this later in the article. Let’s start here: What is a shower tray?

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

The before”:

The use of the copper tray changed to using 4-pound lead sheets (it weighs 4 pounds per square foot, giving it its name), because it is very malleable and can be easily shaped on site. A contractor could measure the size needed, go out to the garage or driveway, crimp the corners as needed with a 2×6 rubber mallet, folding the corners over each other and overlapping so all the edges are on top . At 4 pounds per square foot, it was heavy enough to lug around the house, but it could be done with two people and could be folded in on itself, as it’s so malleable, for getting through narrow 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, the drain flange could be attached, making a tight seal. An adjustable shower drain was then threaded into the flange and gravel was placed around the drain holes to protect them from mud from the deck that was installed below. Deck mud is a dry cement, moistened enough for the cement to hold its shape, allowing it to pack and create the slope necessary for water to flow into the drain.

The “Prepend”:

This is where many of those who take on the task of building their own shower, without any experience in it, make a mistake. Pre-slope is a slight slope of the floor that drains into the shower drain, created with dry pack cement before installing the shower tray. Despite what you may think, water can and will penetrate all the way through the tile, mortar, and concrete above the shower pan, all the way down to the shower pan. In the absence of a prior slope under the shower pan, the pan will lie flat on the floor surface, preventing concrete water from seeping down and into the shower drain drain holes. When concrete remains wet, 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 (it isolates the concrete from floor movement), then staple a layer of Metal Lath. Mix cement with enough water to hold its shape and pack it down creating a 1/8″ thick slope in the drain, toward the edge of the shower at a slope of approximately 1/4″ per foot. On a concrete floor, the felt paper is not necessary, the concrete can be applied directly to the floor.

Some point between “Before” and Now:

Labor time was greatly reduced when the use of vinyl membranes replaced the old lead pans. It can be easily rolled out, molded into place in the shower, fold excess liner back on itself at corners, fold over front shower curb, and use a CPE bonding adhesive (in a can like PVC cement) to seal patches over corners . A newer type of tiled shower drain was used with the vinyl membrane, like the one shown to the left.

The rubber membrane must be wrapped into the wall NO LESS THAN 3 INCHES above the intended final height of the shower threshold (curb or dam). Before wrapping the membrane on the sidewalls, install pieces of 2×10 board between the studs to provide solid support for the sheathing and places to nail the sheathing to the wall. Nails or other fasteners should not be used anywhere except along the top perimeter of the pan liner to prevent nail hole leaks.

After the pan liner is installed, metal lath can be wrapped around the shower surround, which is made from 3 2×4s nailed on top of each other creating a 4.5-inch-high sill, and cement can be packed on the slat and on top. from it, shaping the concrete into a smooth, square surface to apply the tile.

However, I always take an easier route and use the perfect kirb Product Manufactured by Mark E Industries – A plastic product that is easily assembled to form a cage around the lined shower threshold, rather than forming the metal slat.

Concrete board, 1/2″ thick 3’x5′ sheets, can be measured, cut, and installed to the walls with weatherproof screws (to prevent rust stains from getting through the grout later, since that normal screws rust). The concrete board should be installed with a 1/2″ gap between it and the pan liner, pressing the liner into the wall against the studs and 2×10 boards.

The actual concrete slope:

Once the threshold is complete, create the concrete slope within the shower pan liner, taking care to make the surface as smooth and level as possible to allow the small tiles to sit better when laying the tiles. A chalk line can be made around the concrete board on the walls as a guide line, giving a slope of approximately 1/4″ – 1/2″ per foot from the adjustable shower drain to the shower walls .

Again, I take the easiest and fastest route, using Mark E’s Quick Pitch Kit, which includes a plastic ring to fit around the shower drain (protects drain holes from being filled with concrete) and dowel rods. angled plastic that fit into the ring and are placed around it to radiate out to the corners and sides. They can be easily cut to size with tin snips or a hacksaw. This gives me perfect tone every time, and fast!

Now: The next system MOST people will transition to:

There is absolutely nothing wrong with the method that I just explained to you. It is still used by most contractors and at this point it is the least expensive route. However, as you probably know, new technologies appear every year that revolutionize the way things have been done in construction for decades and centuries.

One system I use now, when homeowners have a bigger budget, uses products made by a German brand called Schluter. They have competitors in their market, but they have led the way and hold most of their market share. All of their products work together to make a shower completely waterproof and can be installed much faster than the previous system just explained.

Schluter contends that even if you properly install a shower with the above system as just described, water can still remain in the concrete for an extended period of time and cause mold problems. With his system, the floor and walls are waterproofed with a plastic membrane and there is no exposed concrete to absorb water under the tile. Water that passes through the tile will drain directly along the plastic membrane into the drain.

Is that how it works:

First, once the plumbing and everything else is done, install concrete paneling on your walls, from floor to ceiling. I bought the Kerdi shower kit from Schluter which has almost everything you need to build a waterproof shower ready to tile. The first element of the kit to use is an expanded polystyrene shower tray. It’s already built to the correct slope, all you need to do is cut the foam (fairly easy to do) to fit the opening. Mix up a batch of Thinset and apply with a notched trowel to the subfloor, then set the shower pan firmly in the mortar.

You can then place a Schluter bench in your desired location, which is basically a large block of Styrofoam, and can also 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 out of treated 2x4s and concrete.

In the shower kit is a product called Kerdi, a plastic sheet with a bright orange fleece tape attached to both sides. The plastic membrane waterproofs the shower and the strap provides a bonding interface for ThinSet to adhere to on both sides; one side to the concrete board wall and tile on the other side.

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

One key point about applying Kerdi to concrete panel walls: mix the ThinSet thinner than normal, to the consistency of pancake batter, because otherwise the concrete panel will absorb the moisture from the ThinSet before it settles. let it settle and Kerdi will be unstuck immediately.

Next, insert the included shower drain disc into a generous amount of ThinSet into the center hole and stick it into the underfloor drain pipe. Then wipe off any excess ThinSet oozing from the holes around the disc ring.

Now install, with ThinSet, a piece of Kerdi in the ground, cutting a hole for the drain. Then install the included Schluter Kerdi shower curb, cut to size, and set with ThinSet. Again, this is easy to cut and install because it’s also Styrofoam. Once installed, install a piece of Kerdi over the shower surround and seal the corners with Kerdi-Kereck, also included in the shower kit. Also, in the openings around the shower valves, install the included Kerdi seal pieces.

Now you have the latest and greatest way to build a finished, mosaic-ready shower tray!

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

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