Careers Business Ownership How to Install Backer Board Before Laying Tile Achieve the Ideal Flat Surface With Backer Board Share PINTEREST Email Print joshuaraineyphotography / Getty Images Business Ownership Industries Construction Retail Small Business Restauranting Real Estate Nonprofit Organizations Landlords Import/Export Business Freelancing & Consulting Franchises Food & Beverage Event Planning eBay E-commerce Operations & Success Becoming an Owner By Juan Rodriguez Juan Rodriguez LinkedIn University of Puerto Rico DeVry University Juan Rodriguez is a former writer with The Balance who covered large-scale construction. He is an engineer with experience managing and overseeing large civil works construction. Learn about our Editorial Process Updated on 01/28/20 Floor tiles should be installed over smooth, flat surfaces. To achieve the ideal flat surface, most contractors rely on the backer board. Cement backer board is a thin layer of concrete designed to be setting surface upon which tile can be installed. The backer board comes in different sizes, and you will pick the right one depending on the type of floor you are installing. Tools for Backer Board Installation When you are going to install the backer board as a floor setting surface, you will need the following tools: 1/4 trowelElectric drillBacker boardScrewsChalk lineFiberglass tape or Alkali resistant tapeAdhesive Once you have your materials and tools, you'll complete the following steps to install your backer board. Design Your Layout Use a chalk line to mark the dimension of the backer board sheets onto the floor. Remember that it is best when joints in the backer board are not aligned with the joints in the subfloor. Using the trowel, spread adhesive and ridge it with the notched side of the trowel. Next, place a sheet of the backer board over the wet adhesive. Remember that the wall gap shall be about 1/4 inch with 1/8 inch between backer board sheets. The purpose of the thin-set is to eliminate voids beneath your backer board. The backer board will not expand, but walls will and if you butt joint the installation, the floor might pop out. Install the backer board in such a way that you won’t have four corners meeting at one single place. By staggering the joints, you will increase the substrate toughness by reducing your weak points. Apply thin-set just one row at a time so you can replace and reinstall them faster and easier. Screw and Joints Once you have placed all backer board sheets, install screws every six to eight inches although every backer board following the manufacturer’s recommendation. Do not use drywall screws as they are not recommended to be used to hold the backer board in place. All of your backer board pieces should be cut before they are placed on the floor. Along the perimeter, screws should be installed at least ½ inch from the edge, but no more than 2 1/4 inches. You will want to go and check every seam. Double the screws in those areas just to be sure it is attached properly. Using the flat side of the trowel, fill the joints with adhesive, smoothing it, so the adhesive extends at least two inches on each side of the joint. The tape will be easier to install with this extra adhesive. Start your screws in the center of the board and work out. It is important to highlight that screws shall not be installed all the way down to the floor joists. Tape Using the vinyl-coated fiberglass tape, cover the joints that have adhesive from the previous step. Cut the tape to your required length. Once the tape is in place, remove any excess adhesive from both sides of the tape. Spread adhesive over the length of the tape using the flat side of the trowel. Do not add a lot of adhesive, as you will want your transition to be smooth. It is recommended if you can get alkali resistant tape so it will not break down as a result of the chemicals present in most thin sets.