What is a Conventional Shower?
February 3, 2011
Where does the highest rainfall occur anywhere in the entire country? Your shower! Some years back Don Halverson-a forensic tile consultant, and Cecil Hunt- a California Tile contractor - did a study on just how much water a shower received in a year’s time. Using a standard flow rate of 2.5 GPM with a 12 minute shower a 36”x36” shower stall used daily receives the equivalent of 1,935 inches per year of rain. That is nearly 20 times Washington State’s Olympic Peninsula, which is the wettest area in the contiguous United States with an average annual rainfall of 105 inches. Roofs and windows get a lot more attention than showers which are seen as more of an ancillary item. Given what we expect them to do and how long we expect them to last managing that massive amount of moisture exposure should be much higher on the list of priorities.
Sadly, relative to the amount of them constructed, there seems to be no installation that fails more often than the good old shower stall. Many of those built in days past were doomed to failure from the day they were constructed, being waterproofed primarily by copper and lead liners. That is the typical life of all metal-based shower pan liner given their long-term chemical incompatibility with cement and water. Modern technology has given us new materials to work with that are resistant to the degradation of materials we used in days past. We now have various types of vinyl pan liners and liquid products that will last indefinitely. While applications of these products require a substantially less skill than working with molten lead or soldering copper, they like their predecessors are very unforgiving of installer error. Some of the modern day products also have additional options like premade curb units, niches, shower seats, and even shower bases that make some of the most difficult problem prone areas of shower construction a simple task. We now have the ability to waterproof virtually any surface, even drywall, for a successful installation. New products available today make it possible for anyone who can read and follow instructions to construct a waterproof shower stall over nearly any surface.
Rather than get into the easy way, for this issue let’s review the traditional shower. Often called the conventional shower, this type of shower is built either entirely of mortar, or more commonly the combination of a mortar floor and backerboard. It is still the most popular method of shower construction. One of the most often emitted steps to creating a long-lasting installation using this method is the pre-pitch of the floor under the waterproofing. Uniform Plumbing Code recommends a pre- pitch of ¼” or 2% slope per foot under the pan liner. This pitch can be achieved by many methods, the easiest being the purchase of one of the many premade foam units. You may also establish this pitch by installing 15# roofing felt or 4 Mil plastic, 2.5 metal lath stapled to the floor, and troweling in a layer of mortar. The mortar’s only function in this part of the application is to pitch the water to the drain. It doesn’t need to be pretty, just the ability to get the water in the shower pan liner over to the top of the drain collar to the weep holes in the collar securing the pan liner. One thing that mortar readily does is absorb water. It is a common misconception that mortar, tile, and grout make a surface waterproof. Grout will readily absorb and pass water through to the mortar shower base. That accumulated water must be able to drain and pass into weep holes in the bottom of the drain assembly. It will not drain properly if the membrane is lower than the weep holes in the drain or if the weep holes are blocked by mortar. There seems to be a never-ending argument that the water will escape one way or the other when it comes to weep holes. It won’t. Trickle some out maybe; allow the shower floor to drain, never. Anybody who has ever taken a shower apart can allude to the fact that it may not have been used in months and the water is still there when they take it out. The weep holes must always be kept open by some means be it pea gravel, a special protector, or broken bits of tile and not plugged with mortar.
The shower floor is only part of the waterproofing (moisture management) requirements. The shower curb and jam are equally important. Most plumbing codes require the waterproofing be extended 3” above the curb all the way around the shower, including jambs. The shower curb should be completely wrapped with the membrane and fastened only on the outside face of the curb. One of the areas most prone to leaks is the joint where you must cut the membrane to go over the curb next to the door jamb. Most manufacturers have premade corners available that make it an easy transition.
Unfortunately they are rarely a stocking item. While all seams are important to the waterproof integrity of a shower, the jamb and curb is a particularly a critical area. Once the liner is completed it should be filled with water and tested. While 24 hours is preferred it must be overnight at a minimum. A few hours is not going to tell the story if there is a leak.
When it comes to wall construction there are a lot of options. The simplest method, once learned, is mortar; however its use is limited by those who have a comfort level to do it. Backer board is the predominate choice. In showers, application of the backer board will vary by the type of product being used. True cement board is the only product that may be installed below the water line into the mortar bed. All others must be placed above the finished floor. Most backer boards require a vapor retarder be placed over the studs prior to application, there are exceptions. For any type of backer board product it is recommended that either the studs be furred out over the shower pan liner that is lapping up the wall or the studs be chiseled out to accommodate the pan liner thickness. Failure to do so will result in creating an out-of-plane condition which will be both an aesthetic issue and require extra work to cut the tile on an angle to accommodate. Chiseling the stud was always my preference. Two or three whacks on a chisel for each stud and you are done. It’s a lot less work than fighting out-of-square conditions.
Wet areas require specific types of fasteners. Backer board screws or hot dipped galvanized roofing nails should be used. Drywall screws are a problem for several reasons. First, they have no rust resistant coating. If you are installing a light colored tile and grout it is not unusual to hear a complaint of a rust colored spot behind the tile 6 months to a year after the installation. You can try and blame it on the water or impurities in the thinset or grout but I have never seen it in my lifetime. The other problem with drywall screws is they have a bugle type head which must penetrate the board to seat flush with the surface. Backer board screws have a corrosion resistant coating and a flat surface that holds the panel firmly in place. The reason for hot dipped galvanized roofing nails (increasingly harder to find) is that electro-plated nails lose their plating when driven through the backer board and are then subject to rust.
All backer board joints should be taped with an alkaline-resistant fiberglass tape and thinset mortar. Standard fiberglass drywall tape is not alkaline resistant. If you ever had a fiberglass tape disintegrate as you installed it you have discovered the reason why alkaline resistant tape is recommended. The adhesive that holds the strands of fiberglass together in drywall tape has a low pH resistance. Portland cement is highly alkaline and will cause the tape to fail. The joints should be bedded flush with thinset mortar, not drywall compound. This can be a challenge if the drywaller is installing the backer board, which is increasingly common. Also increasingly common are complaints about cracked or loose tile where the joint compound had delaminated from the backer board. Always use a suitable thinset mortar to install tiles on the wall as well as the floor. It would not be completely accurate to say mastic or premixed thinset will not work. In some if not many instances it will. But, industry methods call for thinset mortar in wet areas to avoid any chance of problems. It has always been my opinion that use of anything but cement-based setting materials in a wet area notes lack of training and professionalism on the part of the installer.
There are many other options and caveats for showers, such as any shower can benefit from complete waterproofing, not just the floor; and all niches, shelves, and seats need to be waterproofed and pitched to the drain. But, space does not allow a more thorough discussion in this issue. While 2010 has been little slower in the inspection business, it has not been much different than 2009 in claims types. The leaders remain hundreds of leaky showers and, believe it or not, a similar amount of claims related to lack of movement accommodation in floors. One was every unit in a 21 story building. I would be very happy not to see any of you under such undesirable circumstances. But if by chance I do, please let me know you’re an FCI reader and maybe we can write a story about all the things that went wrong. Nobody ever calls me when things go right.