By Becky Serbin, National Tile Contractors Association Education and Curriculum Director
Gypsum board products have been used as a base to set tile for probably close to 100 years. However, the true introduction of backer boards began in the 1960s when Paul Dinkel created the first cementitious backer board (cement board) product, manufactured and sold by Custom Building Products, called Wonderboard. Today, the backer board market has exploded to include cement board, fiber cement backer board (fiber cement board), coated glass-mat water-resistant gypsum backing panel (coated glass-mat panels), MgO (magnesium oxide) board, foam board and several backer boards that can only be used in dry areas.
Our focus today is on backer boards that can be used in showers (wet) or dry areas. So how do you know which backer board you should use? Unfortunately, there isn’t an easy answer.
While backer boards can be manufactured with different cores, they do have some things in common. They are lighter weight than mud floors and walls, they have varying degrees of moisture resistance, and a backer board does not fix a bad floor joist or wall stud installation. Floors and walls must meet the substrate requirements found in ANSI A108.01, even when a backer board is used in the tile assembly. But this is where the similarities stop. Each uses a different fastening system, some require vapor barriers in wet areas while others don’t, some can be used in exterior applications as a tile backer, and some backer boards don’t currently have an industry standard.
One of the easiest ways to understand differences between backer boards is by looking through the Tile Council of North America (TCNA) Handbook at all the different methods. Many methods look similar but have a different backer board listed. For example, B415 shows two details, one for cement board and the other for fiber cement board. While both details look very similar, the fiber cement board is not shown in the shower pan. Next, review B420 which is specific to coated glass-mat panels. This is again slightly different than both details in B415—this backer board does not have a vapor retarder membrane behind it because of the low-perm barrier on the face of the panel. When using any backer boards, make sure you are referencing the TCNA Handbook and using the correct method for the backer board you are installing.
Since we are talking about the TCNA Handbook, you may notice there is only one foam board method in the book. This is specific to a cement-coated foam board which has an ASTM standard. The TCNA Handbook committee does not like to accept products without a standard in place, which is why there are no other methods for foam boards. Efforts are underway to develop a foam board standard but until it has been approved by the ASC A108 committee for the ANSI tile industry standards, you will need to contact your specific foam board manufacturer and follow their instructions.
Fasteners are another big difference. Cement board screws are recommended for cement board and fiber cement board because they seal to the surface by using the teeth on the underside of the head to go into the board. However, these screws should not be used on foam board or coated glass-mat panels because they will chew up the moisture barrier surfaces. And foam boards are even more complex because some require washers and fasteners while others just require a fastener. No matter what, if you are working in a wet area, make sure your fasteners are corrosion resistant.
If you do renovation work, there are many additional factors you need to consider. You may need to be concerned about the weight of the backer board. If you must take it up an elevator, is there a weight limit? If you must carry the product up multiple flights of stairs, what is the size and weight of the product your team can handle? What is the stud spacing of the walls? Most backer boards state a maximum 16” on center while some state 24” on center. Can your backer board be used with the current stud spacing or do you need additional backing or bracing to the wall? This is information your backer board manufacturer can provide.
Another consideration is the warranty on the product. Let’s go back to TCNA Handbook method B415 and assume you did all the required installation; it does not mean you also met the manufacturer instructions. For example, method B415 states a vapor barrier is optional, but a manufacturer may require it for the warranty if their product is used in a wet area—so make sure that you also know what is required by the manufacturer.
With all these things to consider, we reached out to NTCA Five-Star members to get some feedback on the backer boards they use and why. The brand names have been removed from their responses.
“We typically use a foam board on the walls and apply a liquid applied membrane on top. We find this to be a system we can warranty and have the confidence it will perform and have longevity. We typically float floors due to the age and the movement of the older buildings, with height restrictions we use ¼” or ½” fiber cement backer board,” said one contractor.
Another noted, “While we use several different backer boards annually, our go-to backer board is coated glass-mat water-resistant gypsum panels. We use both ½” on walls and ¼” on most residential floors. Although we don’t hang much backer board on commercial jobs, most of what the drywall contractors hang for us to tile over is either coated glass-mat water-resistant gypsum panels or cement board. We also install some cement board when conditions warrant (exterior or installing heavier material). Our guys seem to prefer the ¼”, 4’ x 5’ gypsum panels we’re using for floors—it’s just the right thickness to member up with adjoining hardwood flooring for most tiles.”
A different NTCA Five Star member explained, “We switched from cement board to MgO board about five years ago. Our reasoning was because MgO does not contain silica, it’s lighter, easy to cut with a utility knife, holds fasteners better and was at a competitive price.”
Another stated, “We have been using foam board for several years. Even though we have to deal with the fiberglass ‘itch’ sometimes, it’s still the easiest to install and the most cost-effective. I’m an old mud guy so we seldom use backer boards on the floor.”
Based on this feedback, it’s easy to see that everyone has a preference and there’s no one-size-fits-all. In fact, some use more than one backer board depending on the application. So how do you know which backer board to use? We have discussed several considerations but other factors to consider include availability in your area, support from the manufacturer, and most importantly, the product you feel most comfortable installing.
To purchase ANSI books or the TCNA Handbook, visit www.tcnatile.com.
About the Author:
Becky Serbin Is the Education and Curriculum Director at the National Tile Contractors Association (NTCA) and has over 20 years of experience in the construction industry. During her tenure at NTCA she has developed NTCA University and the NTCA National Guidelines for Apprenticeship, worked with the NTCA Methods and Standards committee, NTCA Technical committee, TCNA Handbook committee, and the ANSI committee. Prior to the NTCA, she worked for Georgia-Pacific Gypsum.
