That mastic trick for heavy tile keeps failing on my last 2 jobs

I've got 15 years doing commercial tile work and every time I use mastic for vertical backsplashes over 12x24, the tiles start slipping after 30 minutes. The spec sheets say it holds, but I had to tear off a whole subway wall in a Denver office kitchen last month because the tiles slid a quarter inch overnight. Has anyone else found a reliable way to keep heavy porcelain from sagging with mastic, or do I just need to go back to thinset for everything?

2 comments

2 Comments

miles5812d ago

Man, I feel your pain on that one. I finally gave up on mastic for anything larger than a 6x6 subway tile after a similar mess in a restaurant kitchen. What worked for me was switching to a medium-bed thinset and troweling it on with a 1/2 inch notch instead of the standard 1/4 inch. The deeper ridges give way more grab and stop that creep. Also, I started backbuttering every heavy tile, even ones that were pretty flat it makes a huge difference.

the_susan2d ago

@miles581 You're spot on about the backbuttering making all the difference, I learned that the hard way on a vertical tile install where gravity kept winning. Swapping to a bigger notch trowel sounds like a smart move too, the extra bite would definitely help keep those big tiles from sliding around while the thinset sets up. Every job has its own quirks but that medium-bed stuff has saved me more times than I can count with the heavy format tile.