A 12mm notched trowel sounds specific, and it is-so let's talk adhesive thickness, because getting this right can make or break your tiling job. When you drag that trowel through wet adhesive, those 12mm notches (that's about half an inch, if you're more used to inches) leave behind ridges of glue. Think of it like spreading peanut butter on bread with a knife that has teeth-those ridges are even, consistent, and just the right height.
Now, when you press the tile down onto those ridges, they squish flat, right? So the wet adhesive, before you lay the tile, is gonna be around 12mm thick in those ridges. But once you set the tile and press it firmly, that layer thins out to roughly 6-8mm. That's the sweet spot. Why? Because big, heavy tiles-think 16x16 inches or larger, or natural stone like marble or slate-need that extra thickness to stay stuck. They're heavy, so they need more adhesive to grip onto, but not so much that it oozes out everywhere and makes a mess.
Too thin, and the tile might not bond properly-you'll end up with air pockets between the tile and the wall, and before you know it, that tile's loose. Too thick, and you'll have adhesive squeezing out from under the tile like toothpaste from a tube, which means you'll spend extra time cleaning it up (and if you miss some, it dries hard and looks terrible). Plus, thick adhesive takes longer to dry, and the tile might shift while it's setting-hello, uneven floors.
Pro tip: Don't just rely on the trowel size. If your wall or floor is uneven-maybe there's a bump here, a dip there-you might need a bit more thickness to compensate. I once tiled a basement floor that had a slight slope, and even with a 12mm trowel, I had to add a little extra adhesive in the lower spots to make sure the tiles sat flat. But 6-8mm after pressing? That's your target. Measure it if you want-grab a small tile, press it down, then lift it up. The adhesive should cover the back evenly, with no bare spots, and it should be roughly that thickness. Do a test tile first, and you'll save yourself a lot of hassle later.
adhesive trowel from hanke tools
