Black mould in bathroom sealant and grout is a common problem caused by excess moisture, poor ventilation, and lack of regular cleaning. Not only is it unsightly, but it can also trigger allergies and respiratory issues. This guide shows you how to remove mould effectively and prevent it from returning.

Health Warning: Black mould can cause allergic reactions, asthma attacks, and respiratory problems. Always wear protective gear when cleaning mould.

What You'll Need

  • Bleach OR white vinegar
  • Baking soda
  • Spray bottle
  • Old toothbrush or small scrub brush
  • Microfiber cloths
  • Rubber gloves
  • Protective eyewear
  • Face mask (N95 recommended)
  • Old towels to protect surrounding areas
Never mix bleach and vinegar! Mixing them creates toxic chlorine gas, which can be deadly. Choose ONE method and stick with it.

Method 1: Bleach Solution (Fastest & Most Effective)

Bleach is the most powerful DIY mould remover. Works best on non-porous surfaces like tile, grout, and sealant.

1

Prepare the Area

Open windows and turn on the bathroom fan for ventilation. Put on rubber gloves, protective eyewear, and a face mask. Place old towels on the floor to catch drips.

2

Mix the Solution

Mix 1 part bleach with 4 parts water in a spray bottle. For heavy mould, you can use undiluted bleach.

3

Apply and Let Sit

Spray the solution onto mouldy areas. Let it sit for 10-15 minutes — the bleach needs time to kill the mould roots.

Pro Tip: For vertical surfaces, apply bleach-soaked cotton balls or paper towels to keep the solution in contact with the mould.
4

Scrub Away

Scrub with an old toothbrush or small scrub brush. The mould should come off easily. Rinse with water and dry with a clean cloth.

Method 2: White Vinegar (Natural Alternative)

Vinegar kills up to 82% of mould species naturally. It's less toxic but may require multiple applications.

1

Apply Undiluted Vinegar

Pour undiluted white vinegar into a spray bottle. Spray generously onto mouldy areas.

2

Let It Sit

Allow the vinegar to sit for at least 1 hour. For heavy mould, leave it overnight.

3

Scrub and Rinse

Scrub with a brush, then rinse with water. Repeat if necessary.

Note: The vinegar smell will dissipate as it dries — usually within an hour.

Method 3: Baking Soda Paste (For Stubborn Mould)

Baking soda is a gentle abrasive that works well on grout and textured surfaces.

1

Make a Paste

Mix baking soda with a small amount of water to form a thick paste (like toothpaste).

2

Apply and Scrub

Apply the paste to mouldy areas and scrub vigorously with a brush.

3

Rinse and Repeat

Rinse with water and repeat if needed. For extra power, spray vinegar over the paste — the reaction creates scrubbing bubbles!

Method 4: Commercial Mould Remover

For severe mould infestations, commercial mould removers (containing fungicides) may be necessary.

1

Follow Label Instructions

Carefully follow the manufacturer's instructions. Always wear protective gear and ventilate the area.

Removing Mould from Specific Areas

Bathroom Sealant (Silicone Caulk)

  • Bleach method works best on sealant
  • For severe mould that won't come out, the sealant may need to be removed and replaced
  • Use a sealant remover tool to scrape out old caulk, clean thoroughly, and apply new mould-resistant bathroom sealant

Grout (Between Tiles)

  • Bleach or baking soda paste works well on grout
  • Use a stiff brush to scrub grout lines
  • For heavily stained grout, consider using a grout pen after cleaning to restore colour

Walls and Ceilings

  • Vinegar is safer for painted walls (bleach can damage paint)
  • Test on a small area first
  • After cleaning, repaint with mould-resistant bathroom paint

Shower Curtains and Liners

  • Wash in washing machine with bleach (for white curtains) or vinegar (for coloured)
  • Add towels to the wash to help scrub the curtain
  • Replace shower curtain liners every 6-12 months
Important: If mould covers more than 10 square feet (about 3ft x 3ft), or if it keeps returning despite cleaning, you may have a hidden moisture problem. Consider hiring a professional mould remediation specialist.

How to Prevent Mould from Returning

  • Improve ventilation: Use exhaust fans during and after showers. Leave the bathroom door open after bathing.
  • Wipe down surfaces: Use a squeegee or towel to remove excess water from shower walls, doors, and sealant after each use.
  • Fix leaks promptly: Repair dripping taps, leaking pipes, and running toilets immediately.
  • Use mould-resistant products: Install mould-resistant sealant, grout, and bathroom paint.
  • Clean regularly: Weekly cleaning with vinegar spray prevents mould from establishing.
  • Use a dehumidifier: If your bathroom has persistent dampness, a dehumidifier can help.
Pro Tip: Keep a spray bottle of 50/50 vinegar and water in your bathroom. Spray shower walls and sealant after each shower — it takes seconds and prevents mould growth.
When to replace vs clean: If mould penetrates deep into porous materials like drywall, ceiling tiles, or unsealed grout, cleaning won't be enough. These materials may need to be removed and replaced.