How to Deep Clean Grout
Restore grout from gray-black to its original color using baking soda, hydrogen peroxide, or oxygen bleach — no power tools required. Step-by-step guide.
Grout darkens because it is porous — soap film, body oil, and mold spores all penetrate the surface over time. This guide moves through three cleaning tiers — light scrub to heavy oxidation — so the treatment matches the actual soiling level. No power tools required.
The Three Tiers
Start at the tier that matches your grout. Escalate only if the lower tier does not restore the original color.
- Tier 1 — Light soiling: Baking soda + white vinegar. Soap film and surface grime.
- Tier 2 — Dark or yellowed: Hydrogen peroxide paste or oxygen bleach (OxiClean). Organic staining, yellowing.
- Tier 3 — Black mold: Dilute chlorine bleach (1:10 with water). Heavy mildew and mold growth.
What You'll Need
- Stiff-bristle grout brush (1-inch angled nylon)
- Old toothbrush for corners
- Rubber gloves and eye protection
- Two buckets, large sponge, microfiber cloths
- Spray bottle (16 oz)
- Knee pads for floor work
- Ventilation fan or open window (mandatory with bleach)
- Tier 1: baking soda, white distilled vinegar
- Tier 2: 3% hydrogen peroxide, baking soda, or OxiClean powder
- Tier 3: household bleach (5–8%), water for 1:10 dilution
- Finishing: penetrating grout sealer, foam applicator brush
Assess and pick your tier
Inspect grout under a flashlight at a low angle. Compare discolored lines to an area that never gets wet (behind the toilet, inside a cabinet) for the grout's original color. Run a fingernail across a joint — deposits that lift mechanically are Tier 1. Staining that does not budge is Tier 2. Black fuzzy or spotted growth with a musty odor is Tier 3.
Pre-wet the surface
Saturate all grout lines with warm water before applying any product. This keeps cleaning chemicals working at the surface instead of soaking entirely into the grout. For a shower, run hot water for two minutes first. For floor tile, wet the surface, wait two minutes, then blot up standing water.
Baking soda and vinegar
Press a thick paste of baking soda into the grout lines. Let it sit five minutes. Spritz white vinegar directly onto the baking soda — the fizzing reaction lifts surface deposits as CO₂ forms inside the joint. After two minutes, scrub with the grout brush using short strokes along (not across) each joint. Rinse with clean warm water. Inspect dry.
Hydrogen peroxide paste or oxygen bleach
Mix equal parts 3% hydrogen peroxide and baking soda into a thick paste. Apply generously to all grout lines. Dwell for 15–20 minutes, misting lightly if the paste dries. Scrub and rinse thoroughly. Alternatively, dissolve 1 tablespoon of OxiClean (sodium percarbonate) in 1 cup of hot water and apply with a brush. Dwell 30 minutes, scrub, rinse completely.
Dilute chlorine bleach for black mold
Mix 1 part household bleach with 10 parts water in a labeled spray bottle. Open all windows and run the fan. Spray onto blackened joints, dwell 10 minutes, scrub with the grout brush, rinse with three changes of clean water. The rinse is not optional — residual bleach degrades grout and leaves a chalky film. Wait 48 hours before sealing after bleach treatment.
Rinse completely and let dry
Rinse the entire surface with two to three changes of clean water. Dry with microfiber cloths. Allow grout to air dry completely — 24 hours minimum for floors, 48 hours for shower walls. Press a dry paper towel firmly onto a joint and pull it up; if it shows moisture, allow more drying time before sealing.
Apply penetrating sealer
Apply penetrating sealer to grout lines only with a small foam brush, working in sections. Apply, wait 5 minutes, wipe off any product that spread onto the tile face. Allow 10 minutes cure, apply a second coat. Do not expose to water for 24 hours (48 hours for shower grout). Test yearly: water drops should bead on sealed grout. If they absorb instead, reapply.
Common Mistakes
- Mixing cleaning products — always rinse fully between chemicals
- Scrubbing across joints — scrub along each line, not perpendicular to it
- Using steel wool or abrasive pads — metal particles rust and stain; use only nylon bristle
- Sealing damp grout — sealer turns milky and peels if grout is not bone dry
- Vinegar on natural stone — etches marble and travertine permanently
- Skipping sealer after cleaning — freshly cleaned, open-pored grout resoils faster without it
When to Call a Pro
Call a tile and grout cleaning service when: mold covers more than 10 square feet and returns after DIY bleach treatment (indicating moisture intrusion); grout is crumbling or missing in sections (requires regrouting, not cleaning); the tile is natural stone with existing etching or staining; or a truck-mounted steam cleaning ($150–$350) is desired. Steam extraction cleans at pressures and temperatures no consumer product matches and is worth the cost once every two to three years in a heavily used shower.