How to Waterproof a Tile Shower
May 20, 2011
In 1968, I travelled to California to learn how to be a mosaic artist. Thinking California was packed with mosaicists that needed help, I figured in six months I would learn all there is to know, then return home and set myself up in business. Arriving in San Francisco, I searched the phone books, tile shops, stained glass studios, and art supply stores but could not locate a single person making mosaics. Being persistent, I put Plan B into high gear and began looking for a position with a tile company that would teach me how to do high-end work and eventually lead to big dollar mosaic commissions.
Unfortunately, all of tile contractors I spoke with were not interested at all in a laid-off machinist who did not even know what a mortar bed was. Refusing to give up, I learned there were tile repairmen, so I put Plan C into action and after a couple weeks pounding the pavement, I finally located a contractor who did escrow work and specialized in repairing leaky showers. I was disappointed that mosaic artist was not in my immediate future, but that first humble tile job led me into a lifelong adventure with tile. And that all started because at first, I could not figure out why a tile installation would leak.
Tile has a well-deserved reputation as the most durable of all construction materials, but as I quickly learned, waterproofing depended on the installation – not the tile. Forty-three years ago, 99 percent of all the leaky showers I ripped out were mortar bed installations that used overlapping horizontal bands of tar paper, located behind the mortar bed. Although accepted at the time as reliable waterproofing by some installers, these tar paper bands were really only cleavage membranes, and in many cases, the unsealed overlaps actually promoted leaks caused by the effects of capillary action.
The methods I use now did not happen all at once, but instead, resulted from a series of improvements in available materials and subsequent changes in the methods I used. The first step was to seal the overlaps with cold-patch roofing tar. This helped eliminate capillary action where two bands of tar paper overlapped, and the layer of roofing cement helped seal holes made by staples used to hold reinforcing wire. This technique helped prevent moisture from leaking out of the installation, but I wanted to keep moisture from saturating the mortar beds.
The next step was to substitute latex for the water used as the liquid ingredient in mortar beds, thinset mortars, and grouts. Latex grout and mortar additives do not eliminate leaks because they are not designed for that purpose but they will slow moisture penetration considerably.
These methods helped control leaks and slow down moisture penetration, but with heavy use, all mortar beds will become saturated and this causes problems with mold and mildew which are very difficult to control. The final step I took to minimize leaks and help solve the mold/mildew problem – on either mortar bed or thinbed installations – was to install a surface-applied membrane to the tile setting bed. These membranes work well when installed according to each brand’s instructions, but until recently, joining them to a drain in a tiled shower has been a problem. Today, however, there are accessories and drains that make possible a leak-proof connection between a membrane and drain.
An example of a thinbed shower drain is shown in Photo 1. Called an integrated bonding flange drain, it is a non-clamping drain so shallow that it does not incorporate weep holes in its design, and its flange can be joined to a sheet or liquid-applied membrane system. Shown here with its companion sloped floor panels, the drain is an integral part of this waterproofed, barrier-free shower stall. To build this shower, I began by specifying a dropped subfloor floor in the shower area so that after the sloping panels are installed, the perimeter of the panels is flush with the floor setting bed (Photo 1). For the easiest installation, the connection between the bonding flange drain and the waste line should be done (if there is access) after the sloped panels and drain have been installed.
Waterproofing the sloped floor is done (my preference) after the walls have been covered with a liquid-applied membrane system that laps down onto the floor several inches. The next step is to cut reinforcing fabric sections to fit the space (Photo 2), set them aside, cover the floor and drain flange with a uniform coating of the waterproofing paste (Photo 3), embed the fabric – one section at a time (Photo 4) – and cover the embedded fabric sections with one or more additional coats of paste as directed by the manufacturer (Photo 5). Curing between coats and the completed system is determined by brand instructions.
Some local building codes may only allow clamping-type drains – fixtures normally associated with mortar bed floors. But with a special drain flashing, there is a way to incorporate a clamping drain into a thinbed stall shower.
On the following slab-on-grade installation, the process begins by locating the lower drain half below the top of the slab and using a mold (supplied by the drain flashing manufacturer) to shape the concrete around the drain (Photo 7).
With the plug in place to protect the lower drain half, the next step is to slope the concrete slab. To do this, I use a bonded, dry-pack mortar bed (Photo 8) and float a true slope – with no bird baths, flat spots, or negative slopes because this mortar bed will be the setting bed for the membrane and tiles (Photo 9).
Once the sloped bed has cured, I use thinset mortar and the flashing’s compatible sealant to install the drain flashing (Photo 10).
Once the flashing is seated, the system’s sheet membrane can be installed, first in the floor area, then on the walls. With all curb showers, a 24-hour (minimum) water test is advised.