Short answer: usually because something is being left on the floor, not because the tile is stained. The most common causes are detergent residue that builds into a film, dirty mop water spread from room to room, soil packed into matt or textured tiles, hard-water marks, and grey grout making the whole floor look dirty. Each has a simple test and a different fix.
1. Detergent residue
What you see: a dull, cloudy or slightly sticky floor; footprints show quickly; it looks worse in low sunlight.
Test: wipe a small area hard with a damp white microfibre cloth, then with a dry one. If the cloth picks up a grey smear and the spot looks clearer than its surroundings, there is a film.
Why it happens: using more floor cleaner than the label says, “shine” products, or never rinsing. Each mop leaves a little product behind; the film gets thicker and holds on to new dirt.
Fix: stop adding product for a while. Clean with a pH-neutral cleaner at the correct dilution, then go over the floor with clean water and dry it. A thick film needs a stronger alkaline cleaner and rinsing; see how to remove grey film from porcelain.
2. Dirty mop water
What you see: the floor is evenly grey, and the grout is darker than the tile.
Why it happens: after the first room, the bucket is dirty water. Mopping with it spreads a thin layer of soil across the floor, and the grout soaks it up.
Fix: use two buckets (one to rinse the mop), change the water as soon as it looks grey, and wring the mop well. A flat microfibre mop picks up more and leaves less water than a string mop.
3. Matt, stone-look and anti-slip texture
What you see: darker walkways and a patchy floor, even right after cleaning.
Test: look at the surface at a low angle with a torch. If you see dark specks sitting in the texture, that is packed-in soil.
Why it happens: a mop glides over the high points and never reaches the low points of the texture. That is what makes the tile slip-resistant, and it is also what makes it hard to clean.
Fix: scrub with a stiff nylon deck brush and an alkaline cleaner, then rinse and pick up the dirty water (a wet vacuum is best). On large areas, this is where hand scrubbing becomes very slow.
4. Hard water and sand
What you see: whitish or grey marks where water dried, often near showers, kitchen sinks or the pool doors.
Why it happens: in homes with hard water, minerals stay behind when water evaporates. Near the beach, fine sand is carried in and ground into the surface underfoot.
Fix: dry the floor after mopping; put mats at the doors; vacuum before mopping so sand isn’t dragged around. Mineral marks need a mild acidic tile cleaner (see the warnings in the grey film guide).
5. Grey grout
What you see: clean-looking tiles with dark lines between them. The eye reads the whole floor as dirty.
Why it happens: cement grout is porous and takes in dirty water every time the floor is mopped.
Fix: see how to clean porcelain grout.
A better mopping routine
- Vacuum or sweep first, especially sand.
- pH-neutral cleaner, measured, not poured.
- Two buckets, or change the water often.
- A well-wrung flat microfibre mop.
- Every few weeks, a clean-water-only mop to lift residue.
When mopping stops working
If the floor stays grey after you have changed the routine, the film is thick, the texture is packed or the grout is soaked. More mopping won’t reach it. That is what a machine deep clean is for: the right chemistry, a rotary machine to work every tile and joint evenly, and a wet vacuum to take the dirt out of the house. How the deep clean works →
€15/m² for ceramic and porcelain, grout included. +€2/m² if the floor needs an extra pass. Minimum job 50 m² (€750). Get a quote or send photos by email.