Figure 6-13: Clear Floor Space required in kitchens (C) J Wiley, S Bliss Shower Pan & Shower Pan Membrane Construction & Installation: Best Practices
     


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Shower pan choices, installation, troubleshooting: this article discusses the proper construction or installation of cement, pre-fab, or mortar-bed shower pans and shower pan membranes to build a leak-proof shower floor.

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Recommendations for Constructing or Installing Bath Shower Pans

Shower pan during installation (C) D FriedmanThis article series discusses current best design practices for kitchens and bathrooms, including layout, clearances, work space, and accessible kitchen and bathroom layout, clearances, turning space, grab bars, controls, etc. We include advice on choosing and installing kitchen countertops, cabinets, and kitchen or bathroom flooring, sinks, and other plumbing fixtures and fixture controls such as faucets. A list of kitchen and bath product manufactures and sources is included.

The fiberglass shower pan shown at left was placed and secured to the floor during bathroom construction, then protected from damage with cardboard pending installation of shower enclosure, plumbing, controls, and door.

Photo courtesy Galow Homes.

As explained in Chapter 6 of Best Practices Guide to Residential Construction:

A shower pan must be completely watertight and able to hold pooled water should the drain get clogged.

Most are built in place over a mortar bed with a waterproof membrane liner.

However prefabricated setting beds have also become available recently.

Guide to Using Prefab Cement Shower Pans

Collapsing leaking shower pan (C) D FriedmanOur collapsing, leaking shower pan/floor installation (left) illustrates why site-built lead lined shower pans are a "lost art" and why most contractors opt for pre-fab shower pans of cement, fiberglass, or other materials.

For standard shapes and sizes, one option is to install a prefabricated pan made from 40-lb polystyrene foam coated with a reinforced cementitious coating that is ready to receive tile. These range in size from 36x36 inches to 36x60 inches and come pre sloped with a built-in drain.

One unit, called Pro-Form (Bonsal American) is bonded to the subfloor with latex modified thinset, coated with a liquid waterproofing membrane, and is then ready to tile. As long as the subfloor is sufficiently stiff to prevent flexing, these units should perform well with 4x4–inch tiles. Smaller tiles may exert too much of a point load for the underlying foam, while larger tiles can cause problems with the slope angle.

How to Install Prefab Plastic Shower Pans

A less expensive option is to combine tiled walls with a one-piece fiberglass or acrylic shower pan (not to be tiled). These are the same materials used in one-piece shower or shower-tub units. A few companies also sell stand-alone solid-surface shower pans.

Like other plastic units, these must be properly supported underneath to prevent flexing and cracking. Some require setting in sand, wet mortar, or plaster. In general, acrylic units cost more than fiberglass but are stronger and less prone to flexing and cracking.

How to Build Mortar-Bed Shower Pans & Install a Shower Pan Membrane

Built-in-place shower floors using a mortar bed and modern waterproofing shower pan membranes can provide many years of trouble-free service. For best performance use a heavy-duty sheet membrane, such as 40-mil Chloraloy (Noble Company), which is designed for use in shower pans and similar applications.

To guarantee that any trapped water will drain properly, the shower pan membrane is placed on a layer of latex-modified mortar sloped 1/4 inch per foot toward the drain. Two-piece clamping-type drains are designed to seal to the membrane by compression between the upper and lower flanges (see Figure 6-41).

Figure 6-41: Shower drain connection installation details (C) J Wiley, S Bliss

 

Figure 6-41

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

A layer of sealant applied between the shower pan membrane and lower flange serves as backup waterproofing. Weep holes around the bottom of the drain, surrounded by pea gravel or pieces of broken tile, allow any water that accumulates to drain away (see Figure 6-42 below).

The shower pan membrane should run up all sides of the shower, at least 3 inches above the height of the finished curb. Secure the membrane to the framing with galvanized staples or roofing nails along the top edge, being careful to make no holes in the membrane any lower than 2 inches above the finished curb.

At the inside wall corners, the extra membrane material is not cut, but pleated and folded over to lay flat against the framing. Avoid making wrinkles here or along the bottom of the pan.

At the curb, the membrane must be cut so it can fold over the top of the curb. Seal these corner cuts with either prefabricated “dam corners” or patches of membrane caulked in place with Nobleseal 150, a high-performance Kraton-based sealant.

Figure 6-41: Construction details for a mortar bed and tile shower pan (C) J Wiley, S Bliss

 

Figure 6-42

Kitchen and Bath Product Manufacturers, Sources, Associations

Bonsal American www.bonsal.com Setting compounds, grouts, preformed shower pans, curbs, and niches. Also, distributor of backerboards, isolation membranes, and other tile-setting products

Color Caulk, div. of Roanoke Companies Group www.colorcaulk.com Color-matched caulking

Custom Building Products www.custombuildingproducts.com Elastomeric and liquid-applied membranes, self-leveling underlayments, setting compounds, and grouts

Laticrete International www.laticrete.com Trowel-on membranes, self-leveling underlayments, setting compounds, grouts, and sealants

Noble Company www.noblecompany.com CPE sheet membranes, trowel-on membranes, clamping ring drains, and preformed slopes, niches, and curbs

Mapei www.mapei.com Trowel-on and sheet membranes, self-leveling underlayments, setting compounds, grouts, and color-matched sanded caulks

Custom Building Products www.custombuildingproducts.com Wonderboard cement backerboard, Easyboard cement and polystyrene lightweight backerboard, and Rhinoboard fiber-cement backerboard

Georgia-Pacific Gypsum www.gp.com/build Denshield gypboard backer with glass-matt facing

James Hardie Building Products www.jameshardie.com Fiber-cement backerboard

National Gypsum www.nationalgypsum.com Permabase lightweight cement and polystyrene backerboard

Schluter Systems www.schluter.com Kerdi tile membrane goes directly over drywall or other substrates

T. Clear Corp./Fin Pan Inc. www.finpan.com Util-A-Crete lightweight concrete backerboard

U.S. Gypsum www.usg.com Durock cement backerboard

W. R. Bonsal www.bonsal.com Extruded polystyrene backerboard with fiberglassreinforced cement facing

-- Adapted with permission from Best Practices Guide to Residential Construction.

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