How to remove mildew from bathroom tile grout and reseal with mildew-resistant product
Mildew in bathroom grout is common but manageable with a little time and the right products. This guide walks you through safely removing mildew, cleaning and drying the grout, and resealing with a mildew-resistant sealer so you get lasting results. Follow the steps in order and work carefully in a well-ventilated space.
Step 1: Ventilate and gather supplies
Open a window and run an exhaust fan for at least 10 minutes before starting and while you work to reduce fumes. Gather gloves, eye protection, a stiff nylon brush or grout brush, an old toothbrush, a spray bottle, 1 cup of household bleach or 1 cup of 3% hydrogen peroxide for sensitive surfaces, pH-neutral tile cleaner, rags, paper towels, a utility knife or grout rake, painter's tape, and a mildew-resistant grout sealer (enough for 50–100 square feet).
[Illustration: bathroom window open with cleaning supplies laid out on tiled floor]
Step 2: Test cleaner on a small area
Spray a small inconspicuous 2x2 inch area of grout with the chosen cleaner and wait 10 minutes to confirm there is no discoloration or damage to tile or grout. Testing prevents surprises and protects porous or colored grout from fading. If any change appears, switch to a milder cleaner such as diluted dish soap and water or 3% hydrogen peroxide.
[Illustration: person spraying small grout patch with cleaner and checking results]
Step 3: Loosen surface mildew
Spray the affected grout lines with the bleach solution or hydrogen peroxide and let sit for 10 minutes to kill mildew spores. Scrub with a stiff nylon brush using firm back-and-forth strokes for 2–5 minutes per square foot until stains lift; use an old toothbrush for corners and tight joints. This removes surface staining and exposes stubborn mildew for deeper cleaning.
[Illustration: hand scrubbing grout line with brush and foam cleaner visible]
Step 4: Deep-clean stubborn areas
For persistent stains, apply a paste of baking soda and water to the grout, spray the paste with vinegar or hydrogen peroxide, and let fizz for 5 minutes before scrubbing. Repeat application and scrubbing up to two times if needed, but avoid metal brushes that can damage grout. Rinsing between attempts prevents chemical buildup and helps you judge progress.
[Illustration: close-up of baking soda paste applied to grout with fizzing reaction]
Step 5: Rinse thoroughly and dry
Rinse the tile and grout with warm water using a sponge or wet vacuum until no cleaner residue remains; expect 5–10 minutes of rinsing for an average shower. Dry grout completely with clean towels, then air-dry for 24–48 hours or use a fan or dehumidifier to speed drying; sealers will not bond to damp grout. Complete dryness is critical to prevent trapped moisture and future mildew growth.
[Illustration: person wiping tiles with towel and fan running in bathroom]
Step 6: Remove and repair damaged grout
If grout is cracked, powdery, or missing more than about 1/8 inch depth, remove the loose grout with a grout rake or utility knife and vacuum the joints. Mix and apply new grout following the manufacturer's mix ratio and tool it into the joints; allow the new grout to cure 24–72 hours as directed. Repairing compromised grout ensures the sealer can form a continuous, protective barrier.
[Illustration: hand using grout rake to remove damaged grout from joint]
Step 7: Apply mildew-resistant sealer
Tape edges with painter's tape to protect tile if needed, then apply a mildew-resistant penetrating grout sealer with a small brush or applicator bottle in a thin, even coat along grout lines. Let the first coat sit 5–10 minutes then wipe excess from tiles; apply a second coat if product instructions recommend two coats. Allow the sealer to cure undisturbed for the full time specified (usually 24–48 hours) before using the shower or tub.
[Illustration: brush applying clear sealer along grout lines with painter's tape on tiles]
- Work in sections no larger than 3x3 feet so cleaners and sealers are easier to manage.
- Use a 1:4 bleach-to-water dilution for general mildew spot treatment; use full-strength 3% hydrogen peroxide instead on colored grout.
- Label and note sealer open-cup time and coverage so you buy enough product; typical coverage is 100–200 linear feet of grout per 8 oz. bottle.
- Replace old, discolored caulk around tubs and sinks after grout is resealed to maintain watertight joints.
- Wear nitrile or rubber gloves and eye protection when using bleach or commercial mildew products; wash hands after finishing.
- Maintain grout by wiping down tiles with a squeegee or towel after showers and cleaning with a pH-neutral cleaner every 1–2 weeks to discourage mildew return.
- Never mix bleach with ammonia or products that contain ammonia — this creates dangerous chloramine gases.
- Do a patch test with any cleaner or sealer on an inconspicuous area; some tiles and colored grout can stain or lighten.
- Keep area well ventilated and avoid inhaling fumes from bleach, vinegar, or commercial sealers; leave the bathroom during extended soak times if necessary.
- Keep all cleaning products and sealers out of reach of children and pets; store opened containers tightly closed and disposable rags in a sealed metal container if soaked with flammable sealers.
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