Figure 6-35: Ceramic and Stone Backer Boards and Underlayments  (C) J Wiley S Bliss Tile Backer Boards: Cement backer, Drywall, Greenboard, Glass-mat Gypsum

  • CEMENT BACKERBOARD Installation - CONTENTS: Guide to choosing and installing ceramic or stone tile backer boards for countertops, splashboards
    • Properties & installation of Tile Backer Boards: Cement backer, Drywall, Greenboard, Glass-mat Gypsum
    • How to install greenboard or drywall as a ceramic tile backer
  • POST a QUESTION or READ FAQs about the properties of different ceramic tile backer boards, their installation & troubleshooting.

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Tile backers: cement board, green board, other products: this article discusses the types and installation details for backer boards used below ceramic tiles for countertops and splashboards, including cement backerboard, drywall, greenboard, and glass-mat gypsum backerboards. We address the installation details for each of these material types.

Also see flooring basics at FLOOR DESIGNS: KITCHEN & BATH and see FLOOR TILE, CERAMIC for K & B.

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Cement Backerboard for Use Under Ceramic Tile: Installation Specifications

Figure 6-34: Ceramic and Stone Backer Boards and Underlayments  (C) J Wiley S BlissThis 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. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

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

Developed specifically for use under ceramic tile, cementitious backer units (CBUs) are made of sand and cement and are reinforced by fiberglass facings or chopped fibers within the material itself. Cement backerboard is impervious to moisture, but may let moisture pass through, so it should always be backed by a waterproof barrier, such as polyethylene sheeting or asphalt-impregnated felt.

Because the material has little inherent strength, it relies on the structure beneath for stiffness when used on floors and other applications subject to significant loads. A variation on cement backerboard, Hardibacker (James Hardie Building Products), is made of fiber-cement. Because it is only 1/4 inch thick, it is usually installed over 1/4 -inch plywood, both for stiffness and to bring it flush with the surrounding drywall.

Cement backerboard should be installed with special backerboard screws (not drywall nails) that have an anti corrosive coating and oversized heads with ridges underneath designed to self-countersink and pull tight. Roofing nails are also acceptable with most backerboards.

Closely follow manufacturers instructions, which vary a little from product to product. Typical installations include:

  • Backerboard on walls: CBUs can go directly over studs at 16 inches on-center or over drywall, and it is fastened with 1 1/2 -inch galvanized roofing nails or special self-countersinking galvanized screws at 6 to 8 inches on-center.
  • Backerboard on floors and countertops: CBUs are bonded to the plywood with a layer of latex- or acrylic-modified thinset (Figure 6-34 above and Figure 6-35 below). Apply the thinset with the flat side of a 1/4 -inch notched trowel, then rake with the notched side to provide a continuous level setting bed. Seat the backerboard evenly with a beating block, then secure with roofing nails or special backerboard screws. Because CBUs provide little added stiffness, it is best to upgrade to a 23/32-inch subfloor.
  • Joint details for Cement Backerboard Under Tile: Leave a 1/8 - to 3/16-inch gap between adjoining sheets of backerboard and at edges. Just before tiling, fill the joints with thinset and cover with 2-inch-wide fiber mesh tape (unless the adhesive manufacturer recommends otherwise). Then embed the tape in a thin skim coat of thinset. Reinforce inside and outside corners with three pieces of 2-inch tape or one piece of 4-inch tape.
  • Obstruction Clearances at Concrete Backerboards: Leave a minimum 1/4 -inch gap where the CBU meets a tub lip, plumbing fixture, pipe, or any restraining surface and fill the joint with a flexible, waterproof sealant.
Figure 6-35: Ceramic and Stone Backer Boards and Underlayments  (C) J Wiley S Bliss

Installation Guide for Drywall Substrate Below Tile

Regular 1/2-inch drywall over 2x4 framing or steel studs 16 inches on-center is a suitable substrate for dry installations. Using 5/8-inch drywall or a second layer of 1/2-inch will provide a stiffer wall. Joints should be taped and one coat of joint compound applied to joints and nails. If tiles will be set in thinset mortar, use thinset with mesh tape at the drywall joints.

Using "Greenboard" Moisture-Resistant Drywall Under Tile

Greenboard in a bathroom construction (C) D FriedmanCommonly called “greenboard,” this offers moderate protection in moist conditions, but it is not recommended in wet areas, such as tub surrounds, unless protected by a waterproof membrane.

In our photo the greenboard has been coated with joint compound and sanded - those surfaces were being prepared for painting rather than for tile installation.

Coated Glass-Mat Gypsum Backerboard Use Under Tile

Competing with cement backerboard, gypsum products such as Georgia Pacific’s Dens-Shield® are designed as tile substrates for damp areas. The gypsum core is treated with silicone to make it water-resistant, and the fiberglass and acrylic facing acts as a surface vapor barrier.

While not as strong as cement backerboard, gypsum-based backerboard installs faster since it cuts and installs like drywall. Installation is with roofing nails or galvanized bugle-head drywall screws, which should be driven flush with the surface but should not break the waterproof skin.

Panels are butted tightly and the joints are taped and embedded with latex Portland cement mortar, also used to set the tile.

In use since 1987, Dens-Shield® is well-suited to tub surrounds and other light-duty wall applications, but it is not suitable for saunas, steam rooms, or other applications facing extreme heat and humidity. As with other tile substrates, follow manufacturer’s instructions closely regarding framing, installation, and tile application.

Ceramic Tile Backerboard Producers

  • Custom Building Products Wonderboard cement backerboard, Easyboard cement and polystyrene lightweight backerboard, and Rhinoboard fiber-cement backerboard
  • Georgia-Pacific Gypsum Denshield gypboard backer with glass-matt facing
  • James Hardie Building Products Fiber-cement backerboard
  • National Gypsum Permabase lightweight cement and polystyrene backerboard
  • Schluter Systems Kerdi tile membrane goes directly over drywall or other substrates
  • T. Clear Corp./Fin Pan Inc. Util-A-Crete lightweight concrete backerboard
  • U.S. Gypsum Durock cement backerboard
  • W. R. Bonsal Extruded polystyrene backerboard with fiberglassreinforced cement facing

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

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