Clean Tile Floor Grout

Grout accumulates grime in a way nothing else does. That porous cement between your tiles acts like a sponge for soap scum, dirt, mildew, and whatever walks across your floor. Over months, white grout turns gray, then brown, then nearly black. The good news: grout cleans up remarkably well with the right approach, and you likely have everything you need already. The key is chemistry and mechanical action. Alkaline cleaners break down organic buildup, oxygen bleaches lift stains without damaging grout, and a stiff brush does the work no mop can touch. This isn't about covering up discoloration with new grout or sealer. This is about returning your grout to something close to its original state, which makes the entire floor look newer and makes future cleaning easier.

1. Clear and sweep the floor completely. Remove everything from the floor. Sweep or vacuum thoroughly, paying attention to corners and baseboards where dust collects. Any loose debris left on the floor will turn into mud when you start cleaning and make the job harder. Use a microfiber dust mop or shop vacuum to get into grout lines.
2. Mix your cleaning paste. In a bowl, combine half a cup of baking soda with enough 3% hydrogen peroxide to form a thick paste, about the consistency of peanut butter. You want it thick enough to stay on vertical grout lines if you're doing walls, but for floors a slightly looser consistency works fine. Mix thoroughly until no dry pockets remain.
3. Apply paste directly to grout lines. Use an old toothbrush or small putty knife to spread the paste along grout lines, working in sections about three feet square. You don't need to cover the entire tile, just load up the grout itself. The paste should sit in the grout channel, not spread thin across everything. Work methodically so you remember which sections you've covered.
4. Let the paste work for ten minutes. Walk away and let chemistry happen. The hydrogen peroxide breaks down organic stains while the baking soda provides mild abrasion. You'll see slight bubbling or fizzing on particularly dirty grout—that's the peroxide reacting with grime. For extremely stained grout, fifteen minutes is fine, but longer doesn't necessarily help more.
5. Scrub grout lines with a stiff brush. Use a grout brush or stiff nylon brush and scrub along each grout line with firm pressure. Work in straight lines following the grout, not in circles. You should see dirty paste lifting away and grout color brightening underneath. For stubborn spots, add a bit more paste and scrub again. This step requires real elbow work—plan on several minutes per section.
6. Rinse thoroughly with clean water. Fill a bucket with hot water and use a clean sponge or cloth to rinse away all paste residue. Wring the sponge frequently and change the water when it gets cloudy. Go over each section multiple times—leftover paste will dry to a white film that requires re-cleaning. For large floors, a wet mop works but you'll still need to hand-wipe grout lines to ensure all residue is gone.
7. Dry and inspect the grout. Use old towels to dry the floor completely, or let it air dry with good ventilation. Once dry, check your work in good light. Grout should look significantly lighter and more uniform. Any remaining dark spots are likely deep stains that may need a second treatment or indicate grout that needs resealing. If the grout is clean but still looks worn, consider applying grout sealer after everything is fully dry.