By Bart Bettiga, NTCA
In order for a tile installation to be successful, the substrate (surface that the tile will be adhered to) must be suitable and properly prepared. In many instances, especially in residential construction utilizing wood frame construction, a tile backer board is an excellent choice for both wall and floor tile applications.
One of the most common areas in the home where tile backer board is used is on bathroom walls, especially in areas exposed to moisture such as showers, bathtubs, and steam rooms. When backer board is selected as a floor tile underlayment and is installed correctly, it provides an excellent substrate for tile in kitchens, entries, foyers, bathrooms, and more.
One of the biggest misconceptions about backer boards is that it adds stiffness, or structural strength to the assembly. This is simply not true. If the floor assembly deflects too much, and does not meet the live and dead load requirements for a ceramic tile installation, adding a backer board to the system won’t fix the problem. Unfortunately, many builders and contractors do not understand this, and the result is often cracked tile and grout, leading to installation failure.
Backer board is selected as a tile substrate because it is an excellent bonding surface for ceramic tile mortars to adhere to. It is also chosen because of its ability to withstand moisture, as evidenced by its use in wet areas. This makes the product ideal in areas on floors that can occasionally be exposed to moisture, like kitchens, laundry rooms, and bathroom floors.
There are many types of tile backer boards, comprised of different materials, and designed for specific purposes. Tile installers should pay close attention to installation recommendations and instructions, and should be aware of the methods the industry recognizes in the Tile Council of North America Handbook (page 20 of 2016 version).
Everyone has an opinion on which backer board is the best for a given area, but it really comes down to personal preference, and understanding the environmental conditions of the application. Some backer boards are not advisable to be used in all instances, and the TCNA Handbook addresses this with a sectional called “Environmental Exposure Classifications” (page 42 of 2016 version), that are also cited in each specific installation method. Make sure to understand these classifications to choose the appropriate backer board and installation materials for the project.
It is very important to follow the manufacturer’s instructions when installing backer board. In wet areas, or in areas where movement is a concern, you also should consider the use of membranes (meeting ANSI A118.10), which at times may be recommended or even required to be applied to the backer board before installing the ceramic tile. The “Membrane Selection Guide” (page 21, TCNA Handbook) is an excellent resource. Individual backer board methods are addressed in the “Membrane Options” section.
Use of membranes is very important and should be addressed with the client during the bid or estimating phase. Often, some tile contractors will bid a project with no membrane option included, even when it most likely needed. If you bid the job the right way, you are probably going to be high in your estimate and not get the job. Use the TCNA Handbook to your advantage, and break out the membrane cost in your bid as an option to be considered, and make sure the client is comparing your bid to a competitor evenly.
There is also a section in the Handbook that addresses proper preparation of the backer board. This is important because in some tile projects, especially commercial applications, the backer board is installed by someone else. This allows the specifier to provide this information to the appropriate company prior to installation. When you are installing backer board, it is an excellent guideline for the tile contractor.
Important considerations for installing backer board properly are the type of thinset mortar to use to adhere the backer board to the subfloor; staggering the sheets and edge joints so as not to coincide with joints in the subfloor; and stagger the joints in adjacent rows so four corners do not come together within the same plane. Always follow the directions of the backer board manufacturer you have selected to use, and be sure to use the fasteners or screws they recommend, too. Any deviation from these instructions could result in the warranty of the product being invalid.
One of the most common installation concerns with backer board is cracking of the tile along the seams of the sheets. Make sure to tape seams and corners according the manufacturer recommendations. You are not a structural engineer, and often you are not aware if the framing system and wood panels on which the backer board and tile will be installed meets applicable code requirements. The section “Preparation by Other Trades” is important, and should be supplied to the builder or contractor to make sure the project is suitable for the tile and installation system being specified. A good example here is natural stone tile. Many builders and remodelers are not aware the framing system requirements for natural stone tile are twice as stringent as ceramic tile. Many natural stone failures could have been avoided if steps were taken during the building process to meet the appropriate building code requirements.
By familiarizing yourself with the industry standards, and the appropriate uses for the different types of backer boards on the market, you can help the builder and client select the right system for the project. If you understand the requirements that you can and cannot control, then you can communicate this to your client, avoid potential failures, and add profit to your bottom line.