What the Proper Thinset Coverage is for Adhering Stacked Stone Rock Panels
Thinset can definitely be an overlooked component of a stacked stone panel installation. There’s often so much prep work with the cementious substrate and waterproofing / crack isolation membrane (when necessary), that all an installer wants to do is just get some panels on the wall to finally see some progress that some of the basics of thinset might start to slip. Apart from getting the right type of thinset to meet the adhesion standard necessary for a stacked stone panel installation and mixing it up to manufacturer’s specification, the other super important thing to consider is making sure enough thinset is being used when installing the panels. In this week’s blog we’ll learn how much thinset is enough, how to check for adequate thinset coverage, and what can happen if not enough thinset is used.
To answer the question “How much thinset coverage is required for stacked stone panels?” we always go with the guidance set forth by the Tile Council of North America which states that any natural stone application should achieve a 95% coverage rate. To put that into perspective, on one of our Standard Series Rock Panels, which is 6”x24”, or 1 sq ft, a 95% coverage rate means that only 7.2 square inches on the back of that panel should be left without coverage. A good visual of 7.2 square inches is the size of an average credit card. When you consider how small the size of one credit card is as compared to 1 square foot you start to realize just how important it is to aim for full thinset coverage when adhering any natural stone products.
The best way to achieve full thinset coverage when installing stacked stone rock panels is to use a combination process of back buttering the panels and troweling / notching the thinset on the wall itself. The back buttering process involves using a small margin trowel to put a thin layer of thinset across the entire back of the panel, filling in any gaps or gouges in the back of the stone. Thinset is then also troweled onto the wall itself then “notched” using a 1/2” square notched trowel. The trowel creates ridges of thinset that are each going to be 1/2” wide by 1/2” tall. If there’s not enough thinset on the wall, the ridges will be incomplete and more thinset should be added and the section re-notched.
As the stacked stone panels are being set, they are pushed and slightly twisted into the notched thinset setting bed. This compresses the 1/2” square notches and allows the thinset to be pushed out all along the back of the panels. Even though it can get a bit messy and takes a little time, it’s a good idea to periodically check a panel for full coverage by using a pry bar to pull it off the wall right after its been set. By visually inspecting the back of it, you’ll be able to see if there are any areas where the thinset is not adhering and make the necessary corrections.
So why all this fuss about some sticky concrete that is behind the stacked stone panels? The fact that stone panels can and sometimes do fall off walls as a result of insufficient coverage is hopefully enough for everyone to take notice! Just have a look at the photo above which shows an installation that is failing. The pattern on the wall clearly shows where the installer took the easy way out and put a couple globs of thinset on the back of each panel and tried to simply stick it on the wall without taking the time to either back butter each panel or trowel and notch a thinset setting bed on the wall. While the primary issue with insufficient thinset coverage on floor tile is breaking the tile when direct pressure is applied to the hollow area, the concern with wall tiles that have insufficient thinset coverage is the build up of moisture in the areas left by the voids behind the panels which, especially under freeze / thaw condition, can directly contributed to the tiles or panels falling off the wall.
Thinset isn’t the most glamorous part of a stacked stone panel installation, but in many respects it is one of the most important. Personally, anything that keeps a panel or tile securely adhered to the wall and in no risk of falling off and causing damage to either persons or property should be just as important as the color selected or pattern it’s installed in. Thanks for learning more about thinset with us today and if you have technical questions related to stacked stone installations don’t hesitate to contact us via our main line and ask for the technical services department and we’ll gladly share our knowledge.