Article submitted by David Taylor of Tile-Experts 2-14-2004

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The Schluter-KERDI Watertight Shower

by David Taylor

Constructing a watertight shower in the traditional method is challenging, whether to the experienced installer or to the do-it-yourselfer (DIYer). The preparation required before the actual installation of tile is both time-consuming and labor intensive. It also requires the use of specialty products and tools that may not be readily available to the homeowner. These products also add a considerable amount of weight to the structure of the home.

Even when properly done, these installations are not ideal. They still allow water to penetrate through the tile layer into the backerboard or mud bed. This water is not easily dispersed and could become a breeding ground for mold and mildew.

Although the Schluter-KERDI products are not new, their use in modern shower construction is gaining momentum since the introduction of the KERDI-DRAIN. Many homes are built with new support methods that may not be able to handle the weight of a traditional shower installation. The KERDI shower system employs products that are lightweight, easy to install and readily available at lumber yards or home centers/box stores.

The premise of this system is not to let the substrate become wet in the first place. Drywall (sheetrock) is the preferred wallboard for the installation of KERDI membrane. Contrary to the popular notion that drywall cannot be used in wet areas, the application of a waterproof membrane such as KERDI allows this gypsum-based product to be used. Although other products such as CBU (Wonderboard, Durock, Utilicrete, etc.), water-resistant drywall and composite boards (Hardibacker, Denshield, etc.) may be used, their higher cost, weight, handling and preparation do not bring additional benefits to your final installation.

Of all tile substrates, drywall is the most readily-available, least expensive and easiest to work with. When building a new home or renovating an old one, the installation of drywall does not need to stop at the shower area to apply a different product, which may have a different method or require special knowledge to install. Quite often, the installation of CBU or specialty backerboard units is not done properly; removal and proper re-installation have to take place before tile is applied.

The drywall does not need any special preparation before the application of the KERDI membrane. Joints do not have to be taped or mudded and there is no need for extra bracing or notching of the wall studs to accept a vinyl pan liner. Since the KERDI membrane is surface-applied, it protects all material beneath it from water penetration and damage.

One of the most intimidating steps for a DIYer using the traditional method is the installation of the vinyl liner with the pre-slope and final mud bed. Since the KERDI-DRAIN attaches to the waterproofing membrane on the surface, only one sloped mud bed is necessary. Since only one bed is used, the overall height and weight of the floor is reduced. The formation of this mud bed is made easier because the drain flange is pre-sloped and doesn't have weep holes that may be accidently covered up. It is a perfect screeding guide, which allows the installer to complete the once-tedious steps of sloping one mud bed, applying the liner and forming the final mud bed to be condensed into one step that is completed quickly and accurately.

With the recent introduction of the KERDI pre-sloped shower trays and ramp, you might not need to use a mud bed at all. There's even a pre-formed curb that's easy to install. The trays are available in 32" x 60" and 48" x 48" sizings; perfect for a great number of installations. Each product is easily cut to any size with a wood hand saw or box cutter. Using the tray, curb, drain and membrane, it is quite possible you could complete the preparation work and be ready to tile your watertight shower in one afternoon! Using the former method, you could spend up to four days preparing your shower without it being watertight.

When it comes to installing the tile, the KERDI-DRAIN's 4" square grate design allows you to use larger tile on the shower floor. This will decrease the time needed to install it. It is adjustable until the time you put the tile against it. Because you're able to use a larger tile, you've opened the door to a greater selection of textures and colors over standard mosaics. The grate finishes are available in:

Stainless steel
Brushed anodized aluminum in nickle, copper-bronze and brass

As you can see, the advantages of the KERDI shower system are numerous. Your time and labor costs are reduced; there is no need to purchase additional specialty tools, solvents or heavy and awkward backerboards.

The final result is an long-lasting, watertight installation that some people are already calling the "Classic KERDI Shower".


The best result of a quality installation is a good night's sleep.


Added by John Bridge:

For a complete overview of the Schluter Kerdi shower system, visit the Schluter Systems web site: Nestled in the products section under Kerdi-drain you'll find a very informative video on building the Kerdi-shower.

Log onto the John Bridge Forums for complete advice on the Kerdi shower and on any other tile-related concern you might have.

Check out The Kerdi Shower Book by John P. Bridge.

John has also written a short article on the Kerdi Shower.


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