When applying grout to tile, you’re supposed to wait 15-30 minutes before wiping the grout of the tile while leaving the grout between each tile. This is easier said that done. No matter how good you are, you’ll probably be left with a thin layer of grout on your tile. If you use a light-colored grout on light-colored tile, you won’t notice the haze except at certain angles in certain lighting. The haze can resemble hard water stains. If you use a dark-colored grout on light tile or a light-colored grout on dark tile, the haze is more prominent, and your tile can look dirty. See example below.

You can try to scrub with soap or even a steam cleaner, but that will have zero effect. Luckily, there is an amazing chemical product that can relatively easily remove the grout haze from tile. With Aqua Mix 1 Qt. Cement Grout Haze Remover by Custom Building Products, you just mix the liquid with water, pour some one the tile, wait a while, then rub the haze off. For tougher haze, don’t mix with water. In my case, I poured the liquid at full strength without adding water into a spray bottle, sprayed the liquid on the tile, then wiped the haze off with a rag. As most comments say on the Home Depot product page, this stuff is “amazing”!

