Black Mould Removal

How do you get rid of black mould in a bathroom for good?

Damp, poorly ventilated bathrooms are the ideal home for mould. Getting rid of it takes four steps, and they have to be done in order, because each one removes a food source or a habitat the next one depends on: improve light and ventilation, treat the tiles and grout, replace the silicone, then deal with the ceilings and walls.

The reason people fail at this is that they start at step two. Killing what you can see is satisfying and temporary. Mould cannot grow in dry and brightly lit areas — so ventilation and light are the first step, not the last, and they are what makes the rest of the work last.

Step 1 — Improve light and ventilation

Mould cannot grow in dry and brightly lit areas, so improving ventilation and light is an important first step to getting rid of it.

• Keep windows and doors open as much as possible.
• Consider a ventilation fan to remove steam while showering.
• To improve light, remove blinds and curtains and replace them with opaque glass. You do not need to replace the glass — an opaquing film that sticks onto the existing glass does the same thing.
• Consider a skylight or sky tube to increase natural daylight. Some sky tube kits are straightforward enough to install yourself.

This step costs nothing in product and does more than any of the others. A bathroom that dries out between uses will not sustain a colony; one that stays damp will, whatever you seal it with.

Step 2 — Remove mould on tiles and grout

What you will need: Selleys Rapid Mould Killer and Selleys Grout Stain Whitener.

Rapid Mould Killer is a powerful spray which kills mould fast. Spray it on tiles, shower screens and bathroom surfaces, wait at least 30 seconds, and wipe off, leaving surfaces hygienically clean. It is available in 500 mL and 750 mL trigger packs — the larger one for bigger areas.

Then use Selleys Grout Stain Whitener to whiten the grout. This is the step that breaks the cycle rather than just cleaning it: Grout Stain Whitener contains a fungicide to help prevent mould re-growing over it.

Patch test before you spray a whole wall. On some matt finish tiles, or in hard water areas, staining may occur. Rapid Mould Killer is not suitable for fabric, mirror tiles, metallic surfaces, or older baths or basins. Test an inconspicuous area first and check the pack for the full safety directions before use.

Why 30 seconds, and why wiping matters

The 30 second minimum is dwell time — the product needs contact time to work, and spraying and immediately wiping does very little. Equally, wiping off afterwards is not optional. What you are removing is dead mould and the residue it grew in, and leaving it in place leaves a starter layer for the next colony.

Step 3 — Replace the silicone

What you will need: Selleys Sealant Remover and a quality bathroom silicone.

Black spotting on the silicone corners around showers and baths is unsightly and unhygienic, and it cannot be cleaned out. The colony has rooted into the silicone itself, below the surface, beyond the reach of any cleaner. Remove all traces of the old mouldy silicone first.

Sealant Remover's method: cut the old sealant back to a thin layer less than 5 mm deep, spread at least a 5 mm thick layer of remover evenly over it, leave it at least 10 minutes, then scrape the softened material away. A second application is sometimes needed. Clean residue and tools immediately with mineral turpentine.

Then apply a quality bathroom silicone. There are two sensible choices, and they differ mainly in how soon you can use the shower again:

• Selleys Wet Area Silicone — a neutral cure, 100% silicone sealant delivering a waterproof and mould resistant seal that will not shrink, crack or peel away. Its technical data sheet gives a cure of 72 hours. Tool it within 5–10 minutes of application with a spatula dipped in detergent water.
• Selleys No Mould — an acetic cure silicone containing Speed Seal technology, waterproof and shower ready 1 hour after application, with full cure at at least 48 hours. Its skin time is 20 minutes and it cures at 2 mm per 24 hours. This is the one to buy if you are in a hurry to use the bathroom.

Selleys' own instruction before laying a new bead of No Mould is to spray Rapid Mould Killer into the gap first, to kill any residual mould, then thoroughly clean the surface with turps and dry it.

For the full method, see how to replace old silicone.

Acetic or neutral cure?

No Mould is acetic cure, which suits glazed ceramic tile, glass and porcelain — the materials most shower recesses are made of. Wet Area Silicone is neutral cure, which is what you want where the joint touches a mirror edge, natural or engineered stone, or another substrate the acid released during acetic curing could affect.

Step 4 — Paint mouldy ceilings and walls

What you will need: Selleys Sugar Soap.

Mouldy ceilings and walls are best treated by painting with a mould resistant paint. First, clean the areas to be painted with Selleys Sugar Soap. Then prepare the surfaces by removing any peeling paint and repairing any cracks or holes. Finally, apply a coat of mould-resistant paint.

Selleys Original Sugar Soap is a professional strength, high performance formula that powers through tough grease and grime, and it is recommended for cleaning surfaces prior to painting. Dilute it into water as directed on the pack — one 750 mL bottle makes up to 30 litres of solution, and it can be used neat with a non-scratch scouring sponge for stubborn or in-ground marks. On walls and ceilings there is no need to rinse.

Take note of its handling directions: wipe it off immediately from aluminium and brass surfaces; rinse it well from glass before the product dries; and rinse floors, baths and shower recesses well after use. It has a pH of approximately 11 and causes serious eye irritation — keep it away from eyes, wash hands after use, and use rubber gloves if you have sensitive skin.

What the products can and cannot do

• Rapid Mould Killer — patch test on matt finish tiles and in hard water areas, where staining may occur. Not suitable for fabric, mirror tiles, metallic surfaces, or older baths or basins.
• Sealant Remover — not suitable for rubber, EPDM or polycarbonate. May affect some surfaces, so test compatibility before use. Do not leave it on porous materials or acrylic-painted surfaces for extended periods, and note it will not remove staining caused by old penetrated silicone oils.
• No Mould — not paintable, so complete painting 7 days before sealing. Not suitable for aquariums, for food and drinking water contact, for permanent water immersion, or for metals other than aluminium and stainless steel. Its mould resistance depends on soap scum and dirt being regularly cleaned off.
• Wet Area Silicone — not paintable. Not suitable for PP, PE or PTFE, for aquariums, for food or drinking water contact, or for permanent water immersion. Store below 30 °C and use within 6 months of opening.
• Sugar Soap — test an inconspicuous area for compatibility and colourfastness before using on clothing, carpet or upholstery.

Why sealing over mould never works

This is the step people try first and it is worth stating plainly. An established mould colony can penetrate a new seal even where the new product contains mould inhibitors. Sealing over live mould traps it against a food source in a permanently damp environment. The inhibitors slow surface growth but cannot stop a colony pushing through from underneath. Within months the black spotting is back, and there is now twice as much material to cut out.

Keeping it away

Mould needs a food source, and in a bathroom that is soap scum, shampoo residue and body oils rather than the silicone itself. Selleys' own maintenance instruction for its wet area silicones is exactly this: regularly clean off any soap scum and dirt, as these encourage mould growth. Combine that with running the exhaust fan during and after showering, and the seal you have just laid will outlast the old one by years.

Common questions about bathroom mould

How long does Rapid Mould Killer need to work?

At least 30 seconds before wiping off.

Can I scrub mould out of silicone?

No. The growth is below the surface of the bead, beyond the reach of any cleaner. The bead has to come out.

Which silicone lets me use the shower soonest?

Selleys No Mould — waterproof and shower ready 1 hour after application. It still needs at least 48 hours to cure fully, and must not be touched in the meantime.

How long does Wet Area Silicone take to cure?

Its technical data sheet states 72 hours.

Will a mould-resistant silicone stop mould on its own?

No. No Mould's own technical data sheet qualifies its mould claim with the condition that soap scum and dirt are regularly cleaned off. Cleaning and ventilation are what make the product work.

What whitens discoloured grout?

Selleys Grout Stain Whitener, which also contains a fungicide to help prevent mould re-growing over it.

Can I use Rapid Mould Killer on a shower screen?

Yes — tiles, shower screens and bathroom surfaces are the listed uses. Avoid mirror tiles and metallic surfaces, and patch test matt finish tiles.

Do I need to rinse sugar soap off the walls?

Not on walls and ceilings, where no rinsing is needed. Floors, baths and shower recesses must be rinsed well after use, and it should be rinsed off glass before it dries.

Can I paint over the new silicone to match the wall?

No. Neither No Mould nor Wet Area Silicone is paintable. Painting has to be completed 7 days before the sealant is applied.

Why does mould come back in the same corner?

Either residue from the previous colony was left in the joint, or that corner stays wet longest. Cut the bead out fully, treat with Rapid Mould Killer, dry thoroughly before resealing, and improve airflow to that corner.

Does more ventilation really matter more than the product?

Yes. Mould cannot grow in dry and brightly lit areas, which is why Selleys puts light and ventilation first in this guide.