Adhesive trowel notch direction makes a bigger difference than I thought

Been doing this 8 years and always just scraped the glue on without thinking about which way the notches face. Last Tuesday in a rush on a bedroom in Portland, I pushed the trowel the wrong way, so the ridges were running parallel to the seam instead of perpendicular. Pulled the seam back after 20 minutes and the glue had zero transfer on one side. Redid it with the ridges across the seam and it grabbed instantly. Anyone else check notch direction on every pass, or am I the last guy to learn this?

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jamesfox23d ago

The "zero transfer on one side" part is what got me. That means your thinset was pulling off the substrate, not the tile. I've seen guys blame bad thinset or cold slab for that, but its usually a mechanical issue. What I haven't seen anyone mention is that it matters more with big tiles and deep notches. A 1/2 inch trowel pushed parallel to the seam leaves these long unbroken glue valleys, so the tile only touches the high spots. Perpendicular breaks those valleys up so the tile can actually squish down and grab everywhere. That bedroom floor probably would have failed in a year. Good catch.