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
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
Cement Backerboard for Use Under Ceramic Tile: Installation Specifications
[Click to enlarge any image]
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.
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.
Figure 6-34 (above) shows one layer of plywood with cement backerboard beneath a tile floor installation. A separate figure, Fig. 6-32 shown below, employs two layers of plywood for a more rigid subfloor design.
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
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,
Above: Figure 6-35 offers design details for a wet-counter using cement backerboard.
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
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,” 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
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.
Subfloor Specifications for Installing Ceramic Tile
I cannot tell if it is specifying one or two pieces of 24/32" plywood for the subfloor. There are diagonal lines in two directions with a horizontal line separating them, which strongly suggests that it's supposed to represent two different materials.
Could you please clarify? thank you!
Two layers of plywood is preferred by tile experts to minimize deflection and thus assure a crack-free ceramic tile job on floors.
Author Steve Bliss notes that our mutual tile expert Michael Byrne also glues the underlayment to the subfloor and adds solid blocking under all joints in the subflooring to further stiffen the floor against movement that occurs as temperatures and moisture change in the building. Certainly wood materials are subject to much more potential movement than ceramic tile, and the object is to avoid cracking.
Steve adds the following:
Tile installation standards are established by the TCNA, the Tile Council of North America.
The detail shown is essentially TCNA’s F150 spec – with the addition of an uncoupling (isolation) membrane. The TCNA spec shows this detail with the tile bonded directly to the plywood, but few tile experts recommend this. ...
TCNA does show a single-layer ¾” T&G subfloor with an uncoupling membrane (F148) and a double-layer detail with min.
3/8” plywood underlayment over a ¾” T&G subfloor with an uncoupling membrane (F147). These are minimum standards and I don’t know anyone in the tile industry who advocates a single-layer substrate.
... a more common recommendation is to use ¾” T&G plywood or OSB (glued and nailed or screwed) covered by a layer of ½” plywood underlayment for tile or ¾” for stone – with an uncoupling membrane under the tile.
Your reader is very observant. The two-layer floor is the preferred wood-frame floor tile substrate of tile guru Michael Byrne, who is considered a bit extreme by some. Michael goes further and glues the underlayment to the subfloor with yellow carpenter’s glue and puts solid blocking under all joints in the subfloor.
His reasoning for this detail is that wood-frame construction moves around a lot (deflection, shrinkage, seasonal moisture) and tile doesn’t. He does a lot of failure inspections, expert witness work, etc., and feels that this detail is pretty bulletproof. Some contractors only go to this extreme with some types natural stone.
Tile installation standards are established by the TCNA, the Tile Council of North America.
Photo: Hardiebacker fiber cement tile board. See more photos below. [Click to enlarge any image]
The detail shown is essentially TCNA’s F150 spec – with the addition of an uncoupling (isolation) membrane.
The TCNA spec shows this detail with the tile bonded directly to the plywood, but few tile experts recommend this.
The uncoupling membrane is critical as it protects the tile from small movements in the wood subfloor. Most membranes are also designed to provide waterproofing if installed according to specifications.
TCNA does show a single-layer ¾” T&G subfloor with an uncoupling membrane (F148) and a double-layer detail with min. 3/8” plywood underlayment over a ¾” T&G subfloor with an uncoupling membrane (F147).
These are minimum standards for tile installation, and I don’t know anyone in the tile industry who advocates a single-layer substrate.
Aside from Michael Byrne, a more common recommendation is to use ¾” T&G plywood or OSB (glued and nailed or screwed) covered by a layer of ½” plywood underlayment for tile or ¾” for stone – with an uncoupling membrane under the tile.
Another option for tile is to use 1/2” Hardibacker instead of plywood underlayment. Above: HardiBacker fiber cement tile backerboard, shown in more detail at NON-ASBESTOS FIBER CEMENT BACKERBOARD
Key Details When Framing Floors for Ceramic Tile - from S. Bliss
· The floor framing should be designed for max. deflection of L/360 (stiffer for stone).
Both subfloor and underlayment should be gapped 1/8”
Underlayment should be exterior-rated “underlayment grade” plywood with no voids.
Joints in underlayment should be offset min. 2” from joints in underlayment.
Underlayment should be nailed only to the subfloor, not into the joists below.
For wet areas use a membrane that provides waterproofing as well as crack isolation – sometimes it’s the same membrane but with different detailing.
Always follow the manufacturer’s recommendation with membranes and setting materials. It’s always a good idea to stick with one manufacturer for setting materials – thinset, grout, colorant, sealer.
Never grout tile joints that abut other materials, planes, or restraints such as : wood, fiberglass/acrylic, tile base, recesses, etc. These joints should be caulked with a high-quality sealant. Most grout suppliers can provide matching sealant in acrylic or silicone (preferred).
There are many choices for the uncoupling membrane. I’ve used both Ditra and Strata Mat – the main difference is that Strata-Mat can use modified thinset to bond the tiles while Ditra requires unmodified thinset.
Both use modified thinset to bond to the plywood – tile installation gets pretty technical nowadays. I’ve used both of these in retrofits going over various substrates including stone and well-bonded vinyl.
FYI: Michael is author of Setting Tile (Taunton Press), which has sold over 100,000 copies, and Tiling for Contractors (JLC Books), which I edited and helped produce in 2009-10, so these details are seared into my brain. I specified the Byrne approach in a bathroom addition for a summer house I built 20 years ago in Cape Code.
The bathroom will be above an unheated porch, so I wanted the extra strength of this approach. Not surprisingly, a couple of contractors who looked at the plans said this was overkill, etc. I said, just do it and I’ll pay for the extra work. Looks like I’ve finally got an acceptable bid and should start work within about 30 days.
BTW, grout joints are the bane of tile jobs, which often get badly stained over time on floors.
The trend today is to use larger tiles and smaller grout joints of 1/8” or less where possible (not possible with irregular shaped tiles). The latest thing is stain-resistant grouts that supposedly don’t need sealing, a cheaper alternative to epoxy grout, which is great but very expensive and difficult to install.
We used Laticrete Permacolor on our recent bathroom remodel, but it is too soon to say how it holds up. Another contractor I know likes TEC Power Grout.
The tile industry is rapidly evolving with new setting materials and membranes coming on the market. It’s a lot to keep up with.
Hope that clarifies this murky subject which inspires a lot of debate. Please note that my TCNA Manual is from 2007, so it’s possible that some specs may have changed (generally they just add new methods, but leave the old).
Fiber Cement Backer Board Products that Do Not Contain Asbestos
The fiber cement backer board shown in our photo above was used to support ceramic tile in an Australian home built ca 1986/1986. Thanks to reader KC, 2017/08/24.
[Click to enlarge any image]
This non-asbestos fiber cement tile backer photo accompanied photographs of black ceramic tile mastic adhesive about which the reader worried of an asbestos hazard. Her question and our reply are at ASBESTOS MASTIC IDENTIFICATION.
This photo of a fiber cement tile backer board stamped "MANUFACTURED WITHOUT ASBESTOS" reminds us that at the time your house was built, manufacturers of tile-backer board and cement board were dealing with customers who wanted to be sure they were not being sold old-stock of asbestos containing products. (Though in fact cement-asbestos is not friable and so when intact is not high risk). So they made a clear stamping for people to see.
Below: James Hardie's HardieBacker® EZ Grid® 3' x 5' cement board showing the product label and a close-up of the material. This is a modern fiber cement board that does not contain asbestos.
Continue reading at FLOOR TILE, CERAMIC for K & B (also used on walls) or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Questions & answers or comments about the properties of different ceramic tile backer boards, their installation & troubleshooting. .
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
Access Ramp building codes:
Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
2005 ASHRAE Handbook : Fundamentals: Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked
Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Gypsum Construction Guide, National Gypsum Corporation
Construction Handbook [purchase at Amazon.com] H17, Technical
Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones