Great question-one I get all the time, especially from folks laying big tiles. Let me break this down so you don't overthink it (I used to overthink everything with thinset!).
First, let's clear up a common mix-up: the "1/2 inch" on the trowel refers to the depth of the notches, not the final thickness of the thinset. When you spread thinset with a 1/2-inch notched trowel, the ridges will be about 1/2 inch tall-but when you press the tile down, those ridges get squished. So what's the final depth? Usually around 1/4 to 3/8 inch.
Let me give you a real example: Last month, I laid 16x16 travertine tiles with a 1/2-inch square notch trowel. After pressing the tiles down, I peeled one up to check- the thinset was about 3/8 inch thick, and it covered 90% of the tile's back (which is exactly what you want). If I'd pressed too hard, it would've been thinner-maybe 1/4 inch-but that's still okay, as long as there's full coverage.
Here's a trick to get it right: Don't press the tile like you're trying to squish a bug. A light, even press is enough to flatten the ridges without making the thinset too thin. And always do a test tile! Peel it up, check the thickness and coverage. If it's too thin (less than 1/4 inch) or there are bare spots, you're pressing too hard-or maybe your thinset is too dry. Adjust, and test again.
The key takeaway: 1/2-inch notched trowel = 1/4 to 3/8 inch final thinset depth. Keep it simple, and trust the test tile.
notched trowel from hanke tools
