Using pre-sealer on porous tiles does make a difference. These are tumbled travertine mosaic tiles, which can act like a sponge for stains. The tiles on the left were stained by our Pacifica Blue, the presealed tiles on the right show a measurable improvement. This is a worse case scenario, and we wouldn’t recommend using such a dark blue with this type and color of natural material. Our presealer recommendation is 511 Porous Plus, which is available online from Amazon and other retailers.