A Kerdi Tray: This foam tray and curb replaces traditional mortar types of installations.


A foam pre-pitch and curb.
Is there any area of greater misunderstanding by installers and consumers alike than waterproofing? I don't think so. There is definitely no greater area of failure per tile installation, though a lack of movement joints certainly competes for the top spot. Allow me to quote from the State Farm Insurance Website to demonstrate the depth of this misunderstanding. The following is a direct quote from their page titled "How to Prevent Water Damage to Your Home": "If the shower walls or floor are tiled, a leak may develop if there are cracks or missing areas of grout."

Hmm. That's news to me, though it is an obviously common misperception. The fact is, if it is properly constructed, your shower shouldn't leak even if there is no grout or caulk (though a lack of caulking or sealant could cause extensive water damage to the wall).

Going online, I entered the keyword phrase "water damage showers" in a search engine. In the first 20 hits I found 14 such references, many from similarly reputable companies. While the misconceptions are many, it is clear that water and vapor problems cause billions of dollars in damages every year, not to mention the latest star in the spotlight, mold damage.

Anyway you look at it, improper construction and poor specification in the area of waterproofing is an enormous liability issue, and showers lead the pack by far. Someone recently asked me how many shower stalls did I feel were properly constructed. Though I have no basis for my conclusion other than personal experience, I would say maybe 20 percent will actually perform for the life of the structure.

The most common cause of traditional shower stall failure is incorrect waterproofing of the curb. The waterproofing layer under the mortar needs to extend over the top and down the face of the curb. It also should return up the jamb a minimum of 3 inches. This can be a challenge if you field-fabricate your corners, but it can be done. All sheet-membrane manufacturers make corners, and life is made much simpler when you use them. Remember, they need to be sealed, not just lapped over.



Membranes may add a safety factor to otherwise high-risk installations.
However, if you nail into the top or back of the curb, all is for naught. There are various methods for avoiding fasteners in the curb. When using a mud-curb method, galvanized wire lath is anchored in the mortar bed on the shower side and nailed into the curb on the outside when wood construction is used. Some enterprising installers will thinset cement board to the wire. There are also pre-made units available that will mount right over the common triple-stud curb. There is not a right and wrong here; however you accomplish it, fasteners must be avoided in the top and inside of the curb so the membrane is not punctured, and it must fully support the tile.

Anytime you waterproof a surface, the water has to go somewhere. In the case of the shower stall, and in many other types of waterproof installations, the floor under the membrane must be pitched to allow for shedding or draining of water. For mortar showers, the additional step of making provisions for the bed to drain around the weep holes is commonly omitted. If this is not done, in time the soap and other little goodies sitting below the drain flange in the mortar bed may cause a very moldy condition that can only be remedied by replacement and, in some states, abatement.

For surface or substrate waterproofing in direct-bond applications, the floor substrate needs to be pitched under the membrane to allow for drainage. Mortar beds should be of equal thickness over a pre-pitched substrate. Keep in mind that water sitting on a waterproof floor for extended periods may cause the floor to effloresce. It will also contribute to the natural growth of the installation, causing increases in dimension in years instead of decades.



A waterproof installation using a standard surface drain.
Did someone mention movement accommodation? We occasionally hear from some unsuspecting end-user who had his floor waterproofed because of splashing in the tub or laundry room overflows, only to find out that, if the waterproofing stops at the wall instead of continuing up, this is also where it drains. And if the waterproofing does continue up the wall, with all penetrations sealed, the water still needs somewhere to go, like down the hallway. Necessary drains are often overlooked in waterproofing applications or else the wrong type are installed.

In the age of a graying population, we are seeing more handicapped showers being installed. Many times, funds are available to assist with the refitting of these homes. These agencies pay only once, and the end-users are most often those in no position to afford costly repairs. If you are involved in a handicapped remodel, waterproof the whole floor and, depending on layout, a good portion of the walls. To stop at the edge of the shower curb will not work when there is no shower "dam" to hold the water in. The water will continue to migrate out in the adjoining areas.

While not technically waterproofing, vapor membranes also play a part in preventing moisture damage. Cool, moist surfaces can transmit water or water vapor to the inside of a wall cavity. Nearly all tile manufacturers, as well as the Tile Council of America wall methods, call for a vapor membrane. The exceptions are gypsum panels and extruded foam board. They typically don't specify barrier, which is a waterproof material with a perm rating less than 1 (4 mil plastic sheeting qualifies).



This cardboard box has been a leak-free cooler for three years.
Most times, a vapor retarder (15-pound roofing felt has a perm rating of 1 to 5) is recommended. In this case, the manufacturer's instructions prevail. If you install a barrier behind a gypsum product, failure is assured. This is why the method is not in the TCA handbook for wet areas, as a membrane of some sort is required on exterior walls under most building codes. Tubs and showers often share or abut an exterior wall, so there is a conflict. This even more of an issue with exterior walls in warmer climates due to the warmth of the wall cavity reacting with the cool, moist interior of the wet tile surface. Regular gypsum panels need to breathe out the back of the panel. In the warm climate situation, the wall rots from the back in.

There are specific instructions in GA 216, the gypsum industry "handbook." I have never in my lifetime seen them followed, nor have other committee members, so the method was removed from the TCA handbook. If they were followed, there would be a very reasonable chance of long-term success. If a regular gypsum product is set on the tub, or the joint at the tub interface is grouted instead of caulked, the clock starts ticking. However, they say, as all backerboard and gypsum-board manufacturers caution, to caulk or seal, not grout, the joint between the panel and the tub to prevent wicking.

Whenever a panel is set directly on a tub or shower floor, or you grout a joint at the tub or base of the shower, the water will migrate up the wall substrate, possibly causing a mold issue and, in some cases, deterioration of the wall panel. If you use mastic, it may re-emulsify. In the case of shower installations, the vapor membrane behind all backerboards except those previously mentioned should overlap the waterproof membrane by at least 2 inches.

Waterproofing presents many opportunities for retailers and installers, and protection for the homeowner. This is not a hard sell to anyone who has ever experienced water or vapor issues. Properly installed, the product can provide protection against damage to substrates and protect the structure from moisture intrusion. Improper installation, or lack of either waterproofing or vapor membranes where appropriate or recommended by the manufacturer, may not only result in loss to your customer but also possibly enjoin you in what lawyers affectionately call the "Mold is Gold" group, and that is somewhere you don't want to be.