How to clean porcelain grout

Why grout goes grey

Porcelain tiles absorb almost nothing; standard cement grout is porous. Every time the floor is mopped, the grout takes in a little dirty water. Over months the lines go from their original colour to grey, and the floor looks dirty even when the tiles are clean.

Cement or epoxy grout?

Cement grout (most floors) is matt, slightly sandy to the touch and absorbs water: a drop darkens it. Epoxy grout is smoother, slightly shiny and water beads on it. Epoxy stains far less and handles stronger cleaning; cement grout needs more care, especially with acids.

What you’ll need

• Alkaline tile cleaner
• Stiff nylon grout brush
• Spray bottle
• Bucket of clean water
• Wet vacuum or towels
• Gloves, knee pads

Step by step

1. Vacuum the grout lines to get the grit out.
2. Spray the cleaner along the grout in a 1–2 m² section. Leave it for a few minutes; keep it wet.
3. Scrub along the line, not across it, with the grout brush.
4. Pick up the dirty solution straight away. This is the step that matters: if it dries, the dirt goes back into the grout.
5. Rinse with clean water and pick up again.
6. Let it dry fully before judging the colour. Wet grout always looks darker.

What damages grout

• Regular acid cleaning (including vinegar) on cement grout. It dissolves the cement and leaves the joint rough and sandy.
• Wire brushes and metal scrapers: they gouge grout and chip tile edges.
• Bleach as a routine cleaner. Fine for mould in a shower now and then; it doesn’t remove dirt and never mixes with acids.
• High-pressure steam on old, cracked grout: it can loosen weak joints.

Should you seal it?

A penetrating grout sealer on clean, completely dry cement grout slows down how fast it soaks up dirt. It is not permanent and needs reapplying over time. Never seal over dirty grout: you lock the dirt in.

When grout is past cleaning

If the grout stays dark after a proper clean, is cracked, crumbles when scratched or is missing in places, it is past cleaning. Regrouting or a grout colour treatment is the fix, and that’s a different trade. We say so from the photos rather than sell you a clean that can’t work.

Why DIY may stop working

A 100 m² floor of 60×60 cm tiles has roughly 330 metres of grout line. Scrubbing that on your knees, and picking up the solution before it dries, is a long weekend. A rotary machine scrubs tile and grout at the same time, and the wet vacuum takes the dirt away as it goes. How we deal with grout →