· Michael Blair
A tile floor that looks dirty is almost always a grout problem. Glazed tile does not absorb anything; the cement grout between the tiles is porous and holds onto everything that lands on it. Ordinary mopping moves dirty water across the floor and leaves it in the grout lines to dry, and over a year or two the lines turn a shade darker than they were. Getting them back is a specific job, and the wrong cleaner does permanent harm.
Why grout goes gray
Cement grout is a sponge on a small scale. Dirty mop water, cooking grease, soap residue and, in a bathroom, body oils and mildew all soak into it. Each mopping adds a little more and takes a little less away, and the low point of the grout line is where the water pools and dries. Grout that was sealed at installation resists this for a while; most residential grout was never sealed, or the sealer wore off years ago.
The other common cause is the cleaner itself. Products that leave a residue, and most all-purpose floor cleaners do, build a film that attracts and holds dirt. A floor that looks worse the more it is cleaned is usually a residue problem.
Products that damage, and what they damage
Acidic cleaners, including vinegar and the bathroom products sold for hard water, etch cement grout and eat the polish off natural stone. Bleach whitens grout temporarily and weakens it over time, and it discolors colored grout. Abrasive powders scratch glazed tile and polished stone. Oil-based soaps leave the film described above.
For ceramic and porcelain tile with cement grout, an alkaline cleaner is the safe and effective choice. For natural stone, marble, travertine, slate, limestone, only a cleaner labeled pH-neutral and safe for stone, because both acids and strong alkalis damage the surface. For epoxy grout, which does not absorb, mild detergent is all that is needed.
- Ceramic or porcelain with cement grout: alkaline cleaner
- Natural stone: pH-neutral stone cleaner only
- Never vinegar, never bleach, never abrasive powder
- Rinse with clean water after any cleaner
The method
Vacuum or sweep first, because grit ground into wet grout is what scratches. Apply the alkaline cleaner, diluted as the label says, and let it dwell for several minutes so it can lift what is in the grout. Scrub the grout lines with a stiff nylon brush, not wire, working along the line rather than across the tile. Then the step that everyone skips: pick up the dirty solution with a wet vacuum or clean towels and rinse with clean water, changing the water often.
Steam cleaners work well on grout, lifting the soil with heat and leaving no residue, and they are safe on ceramic and porcelain. They are not appropriate on stone that has been sealed, because the heat can compromise the sealer, or on floors where the grout is already cracked and loose.
Keeping it clean afterward
Once the grout is genuinely clean and dry, seal it. A penetrating grout sealer soaks in and stops the pores holding dirt, and it makes routine cleaning work the way people expect it to. It needs reapplying every few years, more often in a shower.
Then change the routine. Sweep or vacuum before mopping, use a small amount of a residue-free cleaner in clean water, change the water when it looks dirty rather than when the floor is finished, and dry the grout lines with a towel in bathrooms. A floor treated this way stays close to clean for years rather than drifting gray again.