The most important part of the entire shower project to get right is absolutely the underlayment!
And unsurprisingly, this is where most do-it-yourselfers make a mistake, try to short-cut, or just mess up. Improper construction of the floor pan can lead to leaks, of course, but also mold growth under the tile and mortar layer if proper “pre-tilt” 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 shifted to using 4-pound sheets of lead (it weighs 4 pounds per square foot, giving it that 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, bend the corners as needed with a rubber mallet and 2x6s, folding the corners over each other and overlapping so all edges are on the upper part. Weighing in at 4 pounds per square foot, it was quite heavy to lug around the house, but it could be done with two people and could be folded in on itself, since it’s so malleable, to traverse 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 watertight 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. The mud on the deck is a dry cement, moistened just enough for the cement to hold its shape, allowing it to pack and create the slope necessary for the water to flow to the drain.
The “Prependant”:
This is where many of those who are given the task of building their own shower, without any experience in it, make a mistake. Preslope is a slight floor slope 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 tray, all the way down to the shower tray. In the absence of a pre-slope under the shower pan, the pan will lie flat on the floor surface, preventing water from the concrete from seeping down and into the shower drain weep 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 (isolates the concrete from floor movement), then staple down a layer of Metal Lath. Mix cement with enough water to hold its shape and compact it down creating a 1/8″ thick slope at the drain, toward the shower edge 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.
Somewhere between “Then” and Now:
Labor time was greatly reduced when the use of vinyl membranes replaced the old lead trays. It can be easily extended, molded into place in the shower, folded excess liner back on itself at the corners, folded over the curb of the front shower, and used a CPE joint adhesive (in a can like PVC cement) to seal patches on corners . A newer type of tile shower drain was used with the vinyl membrane, like the one shown to the left.
The rubber membrane must be wrapped into the wall NOT LESS THAN 3 INCHES above the intended final height of the shower sill (curb or levee). Before wrapping the membrane on the side walls, install pieces of 2×10 board between the studs to provide solid support for the siding and places to nail the siding to the wall. No nails or other fasteners should be used anywhere except along the top perimeter of the tray liner to prevent nail hole leakage.
After the tray liner is installed, metal lath can be wrapped around the shower surround, which is made of 3 2×4s nailed on top of each other creating a 4.5-inch-high sill, and cement can be packed on the batten and on top. of it, shaping the concrete into a smooth, square surface for applying the tile.
However, I always take an easier route and use the perfect kirb product made by Mark E Industries – a plastic product that easily snaps together to form a cage around the clad shower sill, instead of forming the metal slat.
Concrete backboard, 3’x5′ sheets 1/2″ thick, can be measured, cut, and installed to walls with weatherproof screws (to prevent rust stains from getting through the grout later, since that normal screws rust). The concrete backboard should be installed leaving a 1/2″ gap between it and the tray siding, pressing the siding into the wall against the studs and 2×10 boards.
The actual concrete slope:
Once the sill is finished, create the concrete slope within the shower base liner, taking care to make the surface as smooth and level as possible to allow the small tiles to set better when tiling. A chalk line can be made around the concrete backboard 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 (it protects the drain holes from filling up with concrete) and tie rods. slanted 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 a perfect tone 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 by most contractors and at this point 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 own most of their market share. All of their products work together to make a completely waterproof shower and can be installed much faster than the previous system just explained.
Schluter maintains that even if you correctly install a shower with the above system as just described, the 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 to 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 just about everything you need to build a tile-ready, waterproof shower. 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 (easy enough to do) to fit the opening. Mix a batch of Thinset and apply with a notched trowel to the subfloor, then set the shower pan firmly into the mortar.
You can then place a Schluter bench in your desired location, which is basically a big block of Styrofoam, and it 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 bright orange fleece tape attached to both sides. The plastic membrane waterproofs the shower and the webbing provides a binding contact surface for the ThinSet to adhere to on both sides; one side to the concrete board wall and tiles on the other side.
Apply 3″ wide Kerdi Strips to all corners with ThinSet. After all corners are caulked, apply Kerdi to the walls and bench, if you have one installed.
One key point about applying Kerdi to concrete panel walls: mix ThinSet thinner than normal, to the consistency of pancake batter, otherwise the concrete panel will absorb moisture from the ThinSet before Let it settle and Kerdi will peel right off.
Next, insert the shower drain disc included in a generous amount of ThinSet into the center hole and tape it to the underfloor drain tube. Then wipe away any excess ThinSet that oozes out of the holes around the disc ring.
Now install, with ThinSet, a piece of Kerdi on the floor, 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 EPS. Once installed, install a piece of Kerdi over the shower surround and caulk 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 newest and best way to build a finished, tile-ready shower tray!
… But we’ll leave that for the next article! Get to work!