Caulk vs Grout: Where Each One Belongs

Grout cracks in corners because corners move. Caulk in plane joints, grout between tiles — get this wrong and your shower leaks.

Grout is a cementitious filler designed for the rigid joints between tiles on a single plane. It's hard, dimensionally stable, and meant to stay put.

Caulk is flexible — silicone or polyurethane — designed to absorb movement. Use it anywhere two different planes meet: tub-to-tile, floor-to-baseboard, countertop-to-backsplash, inside shower corners (vertical and horizontal), and where tile meets a different material.

If you grout an inside corner, it'll crack within months because the two walls move independently with thermal cycling. The crack lets water in behind the tile, and you've got a much bigger problem later.

Match the caulk color to the grout color — every major grout brand sells matching caulk. The bead won't read as a different material, the whole installation looks like one continuous grout line, and you keep the flexibility where it matters.