Ceramic tile on concrete, antique floor in Buenos Aires, Argentina (C) Daniel Friedman Guide to Installing Tile over Concrete Slab Floors

  • FLOOR TILE INSTALL on CONCRETE - CONTENTS: How to Ceramic or Stone Tile Over Concrete Slabs. Using floor leveling compounds when installing tile. Guide to Moisture and Water Barriers for Kitchen or Bath Tile. Moisture Barriers for Kitchen or Bath Tile. Tile Membranes for Wet Areas, Bathrooms, Showers. Expansion Joint Requirements in Tile Surfaces. Using Isolation Membranes to Avoid Cracks in Tile Surfaces.
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How to install ceramic tile over a concrete slab: this article discusses and compares the properties of ceramic floor tile, granite tile, marble tile, natural stone and agglomerate floor tiles. We address the installation details for each of these tile types.

This 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.

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Guide to Installing Tile Over Concrete Slabs

Antique ceramic tile on concrete (C) D FriedmanTiles can be applied directly to a clean, smooth concrete slab with a latex Portland cement mortar. The concrete should be properly cured, be level to 1/4 inch in 10 feet, and have a steel trowel or fine broom finish.

Curing compounds or old adhesives used for carpeting or resilient flooring will act as bond breakers, so they need to be removed before installing the tile.

[Click to enlarge any image]

Either a power-blast cleaning machine or a rotary sander with a coarse carborundum sanding sheet can be used. If the slab has cracks or control joints, a crack isolation membrane should be used (see Tile Isolation Membranes).

Our page top photo illustrates ceramic tiles set on conrete in an antique floor we observed in Buenos Aires, Argentina. At left is another ceramic tile on concrete installation in the same city, with some interesting repairs. This floor was installed around 1920.

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.

Other Tile Substrates Used in Remodeling

Ceramic tile over old ceramic (C) D FriedmanIn remodeling, tiles can be successfully installed over existing ceramic tile, plastic laminate, or resilient flooring (except the cushioned type) that is well bonded. These must be stripped of any sealers or waxes and scarified with a coarse sander before applying the new adhesive. Wood floors must first be covered with plywood or a cementitious backerboard.

Unsuitable substrates that should not be used under tile include oriented-strand board (OSB), lower grades of plywood with voids, and interior grade plywoods such as lauan.

The ceramic tile floors shown at left were installed atop of an existing ceramic tile floor (lower right) and over both concrete and solid core plywood (the upper floor level). The curved floor edge trim and facing were site-built by the editor (DF).

Guide to Using Floor Leveling Compounds For Setting Tile

If a wood floor or slab needs leveling, you can use special cement leveling compounds formulated for use as a substrate for ceramic tile or stone tile. These are either site-mixed from a bag or installed by a specialty subcontractor. Some are self-leveling and others require screeding.

Gypsum-based underlayments are generally not suitable for tile. Most self-leveling compounds can be installed up to about an inch thick. For thicker applications, let the first layer dry before adding more, or fill lower areas with plywood shims before adding the compound. Use exterior-grade plywood with no voids.

Guide to Moisture and Water Barriers for Kitchen or Bath Tile

Although glazed ceramic tile is waterproof, neither the grout joints nor the cement backerboard behind the tile are water barriers. To prevent moisture from passing through the tile and substrate to the plywood or wood framing, a moisture barrier is required in areas subject to high moisture levels or occasional wetting, such as tub surrounds and kitchen counters.

In areas subject to heavy wetting, such as shower pans and some bathroom floors and counters, a sheet membrane or trowel-on membrane should be used to provide full waterproofing.

Moisture Barriers for Kitchen or Bath Tile

On tiled walls, protect the wood framing from water intrusion, using either 6-mil poly or 15-pound asphalt-impregnated felt lapped to shed water. The barrier should go between the tile substrate and the framing. On outside walls, this material can also served as the air and vapor barrier if the joints are sealed with tape or a compatible sealant.

Tile Membranes for Wet Areas, Bathrooms, Showers

Figure 6-36: Installing Tile over Concrete (C)  J Wiley S BlissFull waterproofing is required in construction that must retain water, such as shower pans and tiled tubs. It is also recommended in areas subject to frequent wetting, such as raised tub surrounds, bathroom floors, and counters with sinks. There are two types of membranes: thermoplastic sheet materials and trowel-on membranes.

Sheet membranes can be applied to most tile substrates with either thinset mortar or a proprietary adhesive, and tiles are bonded directly to the membrane. With any membrane, check the label for compatibility with the substrate and adhesives. Most waterproofing membranes also serve as isolation membranes.

Figure 6-36 - elastomeric adhesive sheet membrane used below tile in wet areas.

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

  • Sheet membranes: These single-layer elastomerics, such as chlorinated polyethylene (CPE), are bonded to the substrate—typically cement backerboard, plywood, or a mortar bed—with a compatible thinset mortar or proprietary adhesive (Figure 6-36 above).

    After the adhesive cures, tiles are set onto the membrane with a second layer of thinset. For watertight performance, joints in the membrane are caulked with a proprietary sealant or are solvent-welded. In addition to stopping water, CPE membranes act as an isolation membrane, protecting the tile and grout from movement in the substrate (see Tile Isolation Membranes).

    Examples are Noble-Seal TS (Noble Company) and Dal-Seal TS (Dal-Tile Corp.), both 30-mil thick CPE. Special heavier membranes are designed for shower pans, tubs, and other details that must contain standing water.
  • Trowel-on membranes: These one-part or two-part liquids are troweled or brushed on, some with a reinforcing fiberglass fabric. These are good for less critical areas that are only occasionally wetted, such as countertops, tub surrounds, and some floors.

    They also provide limited protection against cracking due to movement in the substrate when used in conjunction with a reinforcing fabric. Examples of one-part membranes include Laticrete 9235 (Laticrete International, Inc.) and Mapelastic HPG (Mapei Corp.).

Expansion Joint Requirements in Tile Surfaces

Tile and grout are fairly unforgiving of movement in the substrate. To protect against cracking of the tile or grout joints, expansion joints are recommended by the Tile Council of America in the following places:

  • Every 24 to 36 feet each direction; or every 8 to 12 feet in each direction if the tiled surface is exposed to moisture or direct sunlight.
  • Around the perimeter of a room or wherever tile meets a different material or abuts restraining surfaces, such as curbs, columns, or pipes.
  • At inside corners, such as where a countertop meets the backsplash.
  • Wherever changes occur in the backing material, for example, from wood to masonry.
  • Directly over any expansion, control, construction, or cold joint

Expansion joints should be at least 1/4 inch wide and free of grout, backerboard, or tile adhesive. Use an elastomeric caulk with a backer rod or bond-breaker tape to prevent three-sided bonding of the caulk (Figure 6-37 below). Most tile suppliers now carry colored caulks designed to match standard grout colors, or colored caulks can be ordered from Color Caulk (see Kitchen & Bath Associations, Product Sources).

Figure 6-36: Installing Tile over Concrete (C)  J Wiley S Bliss

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

Guide to Using Isolation Membranes to Avoid Cracks in Tile Surfaces

Polymer-modified thinset can absorb small amounts of movement, but where more significant movement is expected, a crack isolation membrane is the safest approach. Examples include tiling over concrete with control joints or shrinkage cracks, over radiant slabs, or over existing tile or other problematic remodeling surfaces. Wood-framed floors with long joist spans of 16 feet or more are also good candidates for isolation membranes.

Tile contractors typically use the same type of elastomeric membrane used for waterproofing, such as Noble- Seal TS (Noble Company) or Dal-Seal TS (Dal Tile). It is applied as described above under “Membranes” (previous page), although joints between sheets do not need to be solvent welded unless waterproofing is also required.

Methods for Slab Crack Isolation When Installing Tile Surfaces

In repair work or other jobs where covering an entire floor with isolation membrane is not feasible, a strip of membrane can be installed over just a crack, change of materials, or control joint where minor movement is expected. In general, this will work where cracks are less than 1/8 inch wide, and there is no vertical movement.

Also, with some types of membrane, the contractor can offset the sealant-filled “soft joints” in the tile, so they do not have to fall directly over the crack or control joint in a concrete slab. In this case, create soft joints on both sides of the crack or joint (Figure 6-38), using a flexible sealant instead of grout. If a crack in the concrete substrate runs diagonal to the grout joints, the soft joint must run in a zigzag pattern on each side of the crack.

Figure 6-36: Installing Tile over Concrete (C)  J Wiley S Bliss

Figure 6-38

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

According to tile expert Michael Byrne, crack-isolation membranes used this way should be three times the width of the tile, but he cautions that the preferred approach is to cover the entire floor with membrane.

This provides better protection against cracking and eliminates the soft joints and the slight bump in the tile surface, which may be unacceptable visually.

Kitchen and Bath Product Manufacturers, Sources, Associations

Ceramic Tile-Setting Material Manufacturer List

  • 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

Ceramic Tile Backerboard Producers

  • 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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