How to Tape Backerboard Joints
Installing backer board is a necessary part of installing ceramic tile over a wood subfloor. You have to install the backer board correctly so that it provides sufficiently stability to prevent breaks. Attach it to the floor with thinset and screws or nails. In addition to attaching it to the floor, you also need to fix the seams between the boards with tape. Here are the basics of taping backer board joints effectively.
Step 1 - Fill the Gaps
When you install backer board, you will notice that the edges are tapered, which allows the boards to meet and forms a small gap. In order to complete the installation effectively, you need to fill this gap and level it off. Apply some thinset to the gap. It is the material that you use underneath the backer board to attach it to the wood subfloor. You will also use it to attach the tile to the backer board. Take a trowel or a taping knife and use it to apply the thinset to the gap. You need to make sure that the entire gap between the boards is filled up with the thinset.
Step 2 - Apply the Tape
Once you have filled the gap with thinset, apply fiberglass tape. Pull out a big enough piece of tape to cover the entire gap, then press the tape down on the gap. It should go directly over the thinset and on to the backer board on the edges. You need to apply the tape while the thinset is still wet.
Step 3 - More Thinset
Once you put the tape down on the joint, cover it with more thinset. Use a trowel to apply a very thin layer of thinset to the top of the piece of fiberglass tape. By using the trowel, you should be able to get a very smooth and level. Make sure that the entire seam is covered with thinset and tape, and that the thinset is flat. If there are any humps at the seam, you will run into problems later when you are installing the tile. Once you have the thinset installed on the tile, allow it to dry thoroughly before installing the tile.