Blotchy grout color is usually a mixing or washing problem
Uneven grout color is not normal, though how uneven it looks is partly subjective. The Tile Council says medium grays and beiges are easier to control than bright colors, whites, and blacks. Cement grout tends to turn gray with time and cleaning, which is why sealers are now recommended to reduce that shift.
Causes on the list
Too much mix water, wiping haze too soon and with too much water, plastic spacers left in the joint, thinset showing in the joint, partial bags when the colorant is uneven, a bag that took on moisture after it was opened, water added after the first mix, skipping the slake, poor packing, dirty sponges, dirty water, dirty tools, and foot traffic before cure are all on the FAQ's list. Some grouts need up to three days before traffic. Porcelain can also pull moisture out of the joint unevenly through tiny pores.
Replacing the joint
The page says it is often hard to tell the cause by looking. The grout can be removed and replaced if that is the only acceptable fix. A defective bag is possible and uncommon. Leftover grout can be sent to the Tile Council lab.
Source
Fetched 2026-10-11 from Tile Council grout color FAQ. The sentences above follow that page. They are not a contractor promise.
Related notes
- Tile notes index
- Grout joint width is a choice, not one required size
- Cement grout is cleaned with alkaline cleaner, not acid
- Backsplash photos
Send photos if you want another person to look at the area. This note does not set a response time.