With the increasing popularity of large tiles, projects can have some additional challenges. Those challenges can be compounded when you're dealing with wall tile instead of floor tile, but first, let's take a step back and talk about the acceptable coverage under tile according to the CTEF.
What is Acceptable Coverage Under Tile?
According to the CTEF, "Tile industry standards require minimum mortar coverage of 80% in dry areas and 95% in wet (showers) or exterior areas
. Natural stone tile installations require 95% coverage in all applications.
This refers to the contact area of the bonding material (thin-bed mortars, large and heavy tile mortars or epoxy adhesives) with both the back of the tile and the surface being tiled."
Now, some may question why it is so important to have that kind of coverage on wall tiles when nobody is walking on them. There are quite a few reasons actually. First, reduced mortar coverage can make tile more susceptible to cracks or breaks. Next, if the wall tile is in an area exposed to moisture (such as outdoors or in a shower), water can seep through the areas where there are gaps. And finally, in freezing temperature, that same water seepage can freeze, expand, and then crack the tile.
As the CTEF states, "The application of the ill-advised spot-bonding trick has become a quick and dirty disaster that almost always fails. This is where dollops of mortar are placed on the four corners and the middle of the back of the tile. This trick can produce a tile surface that is flat with a minimal amount of lippage, but it is impossible to achieve the required 80% dry or 95% wet coverage. Spot bonding, no matter what some people say, is a failure waiting to happen. For this reason, you don't ever want to rely on spot bonding which creates bare spots and voids under the tile."
LEARN MORE: Why You Need to Eliminate Spot Bonding When Installing Ceramic Tile
Why the Focus on Walls Rather Than Floors?
When installing tile on the floor, gravity offers a big assist in collapsing the trowel ridges into the valleys. Simply the weight of the installer can be used. However, when installing tile on the wall, there is no assistance from gravity or the installer's weight and obtaining the required coverage becomes more difficult.
Some Typical Challenges
Larger tiles are challenging to move in the back and forth motion and smaller grout joints do not allow much movement. These challenges may mean that the ridges won't collapse completely.
How to Get the Coverage Needed Under Large Wall Tile
Thankfully, the CTEF has covered the best methods for getting the right amount of coverage in four easy steps. Read below for their recommendations:
1. Check the Flatness
"First and most importantly, always check the flatness of the wall with a 10’ straightedge.
Remember that the ANSI requirement for tiles with any side longer than fifteen inches, the flatness requirement is 1/8” in 10’. This is determined by measuring the distance between the bottom of the straightedge and the substrate.
Flattening the wall with the appropriate flash patch to meet this requirement will make the installation of the tile much easier and faster." - CTEF Blog
2. Comb the Mortar Parallel to the Short Side
"After cleaning and dampening the surface, properly key the mortar into the substrate with the flat side of the trowel and change the direction of the straight line troweling method.
Whichever way the tile is being installed (vertically or horizontally), comb the mortar parallel to the short side of the tile
. This way the trapped air under the tile has a shorter distance to travel.
For example, if a 12” x 48” tile is being installed, the mortar ridges should be the same direction as the 12” side." - CTEF Blog
3. Use Suction Cups as Handles
"Use suction cups applied to the face of the tile. Two suction cups will provide a handle on each side of the tile face which makes moving the tile back and forth more easily accomplished." - CTEF Blog
4. Deeper, Narrower Trowel Notches Give Better Coverage
"Consider using a trowel that has deeper and narrower notches such as a 1/4” x 1/2” x 1/4”, a “U” notch such as a ¾” x 9/16” x 3/8”, or zipper notch. This way the tile needs only to move a short distance each way, yielding better coverage." - CTEF Blog
If you follow the recommendations from the CTEF, you should get the coverage you need and have a successful tile installation. These four small steps will make a huge different in the time and quality of your installations. Another great step to take in improving your installations is to become a Certified Tile Installer. Talk to your local D&B Tile Distributors' tile experts to learn how we can help you achieve that.