Invisible Grout Lines . Smallest size grout lines should not be less than 1/16″. The superior coating used even makes the tile murals resistant to uv damage. Tile, Grout Cleaning Campbell River Tile, Grout Cleaning Specialist from sgfloormaintenance.ca The red devil grout color for pool tile is less convenient and it is more durable. I see masons do it all the time for outside work. 1/16 is the thinner and more preferred grout line as it gives a “more tile and less crap” kind of look.