How to Deep Clean Grout
This guide covers the complete process for deep cleaning cement grout in a bathroom — floor tiles, shower walls, and tub surrounds — using household chemicals and a stiff-bristle brush. No power tools are required for most jobs. The process moves from light cleaning through progressively stronger treatments, stopping at the level of soiling your grout actually has.
Grout darkens over time because it is porous. Soap scum, body oil, mineral deposits from hard water, and mold spores all penetrate the surface. Regular mopping does not remove them — it only deposits a layer of diluted soil on top of what was already there. A proper deep clean uses either mechanical scrubbing, chemical oxidation, or both, depending on severity. This guide covers three cleaning tiers: everyday-dirty, noticeably dark, and black/heavily mildewed. Match the tier to your grout before you buy anything.
What You'll Need
Tools
- Stiff-bristle grout brush (dedicated, not your tile brush) — a 1-inch nylon bristle brush with an angled head reaches grout joints accurately
- Old toothbrush for corners and caulk-adjacent lines
- Two buckets — one clean rinse water, one for mixing
- Large sponge and microfiber cloths
- Rubber gloves and eye protection
- Knee pads for floor work
- Ventilation fan or open window — mandatory for any bleach product
- Spray bottle (16 oz)
Materials — Tier 1 (Light Soiling)
- Baking soda (box, about 1 cup per 20 sq ft of grout)
- White distilled vinegar (do NOT use on natural stone — acid etches marble and travertine)
- Dish soap, a few drops
Materials — Tier 2 (Dark or Yellowed Grout)
- 3% hydrogen peroxide (standard drugstore bottle)
- Baking soda (for a paste)
- Optional: OxiClean powder (sodium percarbonate oxygen bleach) — 1 tablespoon per cup of hot water
Materials — Tier 3 (Black Mold or Heavy Mildew)
- Household bleach (sodium hypochlorite 5–8%) — standard Clorox Regular
- Water for dilution: 1 part bleach to 10 parts water in a spray bottle
- Chlorine-rated respirator mask if working in a tight bathroom
- Never mix bleach with vinegar, ammonia, or any acid-based cleaner. The combination produces chlorine gas.
Materials — Sealing (After Cleaning)
- Penetrating grout sealer (silicone- or fluoropolymer-based) — Aqua Mix Sealer's Choice Gold or equivalent
- Small foam applicator brush
Step 1 — Assess the Grout and Pick Your Tier
Look at the grout in good light, ideally with a flashlight held at a low angle to cast shadow into the joints. Run your fingernail across a representative joint. Identify the color your grout was installed as — check an area that never gets wet (behind the toilet, inside a cabinet) for comparison.
Light gray or tan deposits that come off with a fingernail: Tier 1. Dark brown or yellow staining that won't budge mechanically: Tier 2. Black, fuzzy, or spotted mold with a musty odor: Tier 3. Start at the correct tier. Using bleach on light-soiling grout is unnecessary and accelerates grout degradation over time. If in doubt, start lower and escalate.
Check tile type before choosing a chemical. Ceramic and porcelain are chemically inert — all three tiers are safe. Natural stone (marble, travertine, slate) cannot tolerate any acidic product, including white vinegar. For natural stone, use only baking soda paste (Tier 1) or pH-neutral stone cleaner (Tier 2). Never use bleach or acid on natural stone grout. Visit the bathroom cleaning hub for stone-specific guides.
Step 2 — Pre-Wet the Surface
Saturate the entire grout area with warm water before applying any cleaning product. Use a sponge or spray bottle. Pre-wetting keeps the cleaning product from soaking entirely into the porous grout and keeps it working on the surface longer. It also prevents some products from leaving a residue on the tile face. For floor tile, wet the floor, let it sit two minutes, then blot up standing water before applying product — you want damp, not flooded.
For a shower or tub surround, run the hot shower for two minutes before cleaning. The steam opens the pores of the grout slightly and makes the cleaning product more effective. Close the bathroom door to trap humidity, but open a window for ventilation if using bleach in the next steps.
Step 3 — Tier 1: Baking Soda and Vinegar (Light Soiling)
Spread a thick paste of baking soda directly onto the grout lines. Use a spoon or your gloved fingers to press it into the joint. Let it sit for five minutes. Spritz white vinegar from a spray bottle directly onto the baking soda. The fizzing reaction lifts surface deposits mechanically as carbon dioxide bubbles form and expand in the joint. Let the reaction run for two minutes — it will slow and stop on its own.
Scrub with the grout brush using short, firm strokes along the joint (not across it). Short strokes keep the brush in the joint rather than skating over the tile surface. Rinse with clean warm water and a sponge. Examine results. If the grout is noticeably lighter but still not at original color, escalate to Tier 2. If it looks correct, dry with a microfiber cloth and inspect under a light again when dry — grout can look clean when wet and reveal remaining discoloration once dry.
For soap-scum buildup that is more physical than biological, a paste of baking soda with three drops of dish soap is sometimes more effective than the vinegar fizz. Apply it the same way but scrub without the vinegar spray and rinse thoroughly to prevent dish soap residue from attracting soil.
Step 4 — Tier 2: Hydrogen Peroxide Paste (Dark or Yellowed Grout)
Mix 3% hydrogen peroxide with baking soda to form a thick paste — roughly equal parts by volume. The mixture should hold its shape when spooned onto a vertical surface. Apply generously along every grout line in the area. Allow it to dwell for 15 to 20 minutes. Do not let it dry on the tile face; if the bathroom is hot and dry, mist lightly with water every five minutes to keep it active.
Scrub with the grout brush, working along each joint. The peroxide oxidizes organic staining (soap film, body oil, some mold byproducts) while the baking soda provides mild abrasion. Rinse with warm water, then inspect dry. Most yellowed or tan grout responds well at this tier and does not require bleach.
For oxygen bleach (OxiClean or generic sodium percarbonate): dissolve 1 tablespoon of powder per cup of hot water in a mixing bucket. Apply the solution to grout lines with a brush and let it dwell for 30 minutes. Do not let it dry. Scrub, rinse completely, and allow 24 hours before sealing. Oxygen bleach is gentler than chlorine bleach and substantially safer to use in enclosed spaces. It is the preferred Tier 2 escalation for heavily-grouted shower floors with extensive surface area.
See also: How to deep clean a shower for the full shower cleaning protocol that pairs with this grout guide. For tile that has a grout haze problem rather than a dirt problem, see How to remove grout haze.
Step 5 — Tier 3: Dilute Bleach (Black Mold or Heavy Mildew)
Reserve dilute bleach for mold that persists after oxygen bleach treatment. Mix one part household bleach (5–8% sodium hypochlorite) with ten parts water in a spray bottle. Label the bottle. Open all windows and run the ventilation fan before you begin. If the bathroom has no window and a weak fan, work with the door open. Consider a chlorine-rated respirator for extended work in tight spaces.
Spray the dilute solution directly onto blackened grout. Do not spray the tile face unless the grout is flush with it — bleach will not harm ceramic or porcelain tile but can spot unsealed natural stone and some grout colorants. Let the solution dwell for ten minutes. Mold spores are killed on contact at this concentration; the dwell time allows penetration into the porous grout. Scrub with the grout brush and rinse with three changes of clean water. The rinse phase is not optional — residual bleach accelerates grout degradation and leaves a chalky residue on tile.
If black mold returns within two to four weeks after bleaching, the source is moisture rather than surface soiling. Check the bathroom exhaust fan — it should move enough air to clear steam from a 10-minute shower within 15 minutes. Check caulk lines for gaps that allow water to reach the wall behind the tile. Mold that recurs in the same location repeatedly after proper cleaning is a ventilation or waterproofing problem, not a cleaning problem.
After bleach cleaning, wait at least 48 hours before applying any sealer. Residual chlorine interferes with sealer bonding. The grout should be bone dry and odor-free before sealing.
Step 6 — Rinse Completely and Let Dry
After any tier of cleaning, rinse the entire surface with two to three changes of clean water. The first rinse removes the cleaning product. The second removes the loosened soil. The third is a quality check — if the rinse water is still visibly dirty or sudsy, continue rinsing. Residual cleaning product left in grout joints attracts soil faster than bare grout.
After the final rinse, dry the tile surface with microfiber cloths. Leave the grout to air dry completely — minimum 24 hours for floor tile, 48 hours for shower walls. Do not seal damp grout. Check dryness by pressing a dry paper towel firmly onto the joint and pulling it up quickly — if the towel shows moisture, allow more drying time. Warm, dry air from a household fan directed at the floor accelerates drying significantly.
Step 7 — Inspect Under Direct Light
Before sealing, inspect the grout under a flashlight or task light with the room's main lights off. This reveals remaining soiling that was invisible under overhead light. Note any lines that still show significant discoloration. For grout that resisted all three tiers of cleaning, the only remaining options are professional grout cleaning with a steam extractor, or grout recoloring with an epoxy grout colorant that bonds to existing grout and changes its color permanently.
Grout that is heavily cracked, crumbling, or missing sections in places cannot be cleaned — those sections need regrouting. Deep cleaning should not proceed on grout that is structurally failing. See How to regrout a shower before attempting to clean grout that is physically damaged.
Step 8 — Apply Penetrating Sealer
Penetrating grout sealer is the single most effective way to prevent grout from darkening again. It does not change the color of the grout. It fills the micro-pores with a silicone or fluoropolymer compound that repels water, soap, and oil. The clean, dry grout will absorb the sealer deeply; grout sealed immediately after installation often doesn't penetrate as well as grout cleaned and dried before sealing.
Apply sealer to grout lines only using a small foam applicator brush or the corner of a cloth. Work section by section — apply, wait 5 minutes, wipe off any that spread onto the tile face. Allow the first coat to cure 10 minutes, then apply a second coat. Total cure time before exposing to water: 24 hours minimum, 48 hours preferred for shower grout.
Test seal performance yearly. Drop a few drops of water onto a grout line and watch for 30 seconds. If the drops bead and sit on the surface, the sealer is holding. If they darken the grout and absorb, the seal has worn down and should be reapplied. Shower grout typically needs resealing every 12–18 months. Floor grout in a low-traffic bathroom may last 2–3 years between applications.
Step 9 — Ongoing Maintenance
After deep cleaning and sealing, the grout will stay clean substantially longer with simple maintenance habits. Wipe down shower walls with a squeegee or dry cloth after every use — this removes the soap-film layer before it can penetrate the sealer. For floor tile, a weekly damp mop with a pH-neutral cleaner (not vinegar, which degrades silicone sealer) keeps surface soiling from accumulating.
Spray a light mist of diluted hydrogen peroxide (half water, half 3% peroxide) onto shower grout once a week, leave it for five minutes, and rinse. This routine oxidizes the low level of soap and organic residue before it can polymerize and stain. It takes 30 seconds per application and eliminates the need for a full deep clean more than once a year in most bathrooms.
See all bathroom cleaning guides for related topics, including shower head descaling, toilet deep cleaning, and tile polishing.
Common Mistakes
- Mixing cleaning products. Bleach plus vinegar produces chlorine gas. Bleach plus ammonia (found in many glass cleaners) produces chloramine. Never mix products, and always rinse completely between switching from one chemical to another. At least two complete rinses between products.
- Scrubbing across joints instead of along them. A brush moved perpendicular to the grout joint drives soil into the tile-grout interface and scratches tile glaze. Work parallel to each joint with short strokes for maximum contact.
- Using steel wool or abrasive pads. Steel wool leaves micro-particles that rust and stain grout brown within days. Abrasive pads scratch tile glaze permanently. Use only nylon bristle brushes.
- Sealing damp grout. Sealer applied to even slightly damp grout traps moisture, turns milky, and peels. Wait the full 24–48 hours. Use the paper-towel test before sealing.
- Using vinegar on natural stone. Acetic acid etches marble, travertine, and limestone. The damage is permanent and requires professional stone restoration. Check tile type before choosing any acidic product.
- Skipping sealer after a deep clean. Deep cleaning opens grout pores by removing protective debris. Unsealed, freshly cleaned grout resoils faster than it did before the clean. Apply sealer within 48 hours of cleaning.
When to Call a Pro
Hire a tile and grout cleaning service when: mold is visible on more than 10 square feet of shower grout and returns after DIY bleach treatment (indicating a moisture intrusion problem requiring inspection); grout is crumbling, delaminating, or missing in sections (cleaning cannot substitute for regrouting); the tile is natural stone and has any etching or staining (stone restoration requires diamond-pad polishing, not cleaning); or a steam cleaning is desired — professional truck-mounted steam extractors clean at temperatures and pressures that no consumer product replicates and are worth the cost ($150–$350 for a typical bathroom) once every two to three years.
Choosing the Right Brush
The quality of the grout brush matters more than the chemical. A 1-inch angled nylon grout brush (sold at tile supply stores and online for $8–$15) reaches the joint depth and applies force along the correct axis. Drug-store "grout brushes" are typically too wide and too soft. An electric toothbrush on high speed provides excellent mechanical action for corner joints and caulk-adjacent lines. A manual toothbrush has the right size for detailed work but tires the wrist quickly — use it only for corners and detail areas.
Do not use a wire brush on grout. The metal bristles abrade the grout surface, open additional pores, and leave metal deposits that rust. This applies to all grout types including epoxy grout.
Grout Types and Their Cleaning Limits
Cement grout (most common). The default for most bathroom installations. Responds to all three cleaning tiers. Must be sealed. Susceptible to mold and staining if not sealed and maintained.
Epoxy grout. Used in commercial kitchens and high-end bathroom installations. Non-porous, highly stain-resistant, does not require sealing. Cleaning is almost always Tier 1 only — if epoxy grout is dark, it is usually grout haze from installation, not soil. Do not use bleach on colored epoxy grout without testing in an inconspicuous area first; some pigments are not bleach-stable.
Unsanded grout. A finer-particle cement grout used in joints under 1/8-inch wide (common in wall tile with very tight joints). Same cleaning approach as sanded cement grout.
Quarry tile grout (paver grout). Very coarse, very porous. Tier 2 and Tier 3 cleaning frequently needed. Penetrating sealer is essential and may need annual reapplication.
Grout Color Restoration (When Cleaning Isn't Enough)
If grout lines are clean after this process but the color is still not what was installed — often because previous owners painted the tile, or because the grout is simply old and discolored below the surface — grout colorant is an effective and long-lasting solution. Grout colorant (Polyblend Grout Renew is a common product) is applied with a small brush to each joint, allowed to cure, and sealed. It changes the grout color permanently to any available shade and adds a surface that is easier to clean than raw cement grout. The application process is time-consuming for a full bathroom floor but well within the DIY skill level.
Colorant applied over dirty grout will not adhere properly. Always deep clean and seal first. If the seal is applied, wait for it to cure, then remove it from the grout surface (not the tile) before applying colorant — silicone sealer prevents colorant bonding in the same way it prevents staining.
About This Guide
Filed by HowTo: Home Edition. This is a Clean × Bathroom guide. It is the marquee grout reference for the Clean lane — the most searched bathroom cleaning topic and one of the highest-signal DIY projects for maintaining a bathroom's appearance and preventing costly tile replacement. The techniques described here cover the full severity spectrum from routine maintenance to mold remediation. Pair with the bathroom cleaning hub for the complete bathroom maintenance workflow.