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How to use mildew treatment

Updated: 23 October 2026

You have a small black patch on plaster or tile, and the bottle does not match the last article you read. One Dulux page says leave a wash at least an hour. A related trade sheet says 24 hours and do not spray. This is how to use mildew treatment on a small hard surface: what to wear, what not to vacuum, and when the label overrides a generic clock. It stops when the surface is clean and dry. The bottles are on the [mildew treatment comparison](/hub/paints-and-varnishes/mildew-treatment). Peter F. updated this page on 23 October 2026. This is public guidance plus listing text, not a lab method. Our amazon.co.uk links may earn a commission at no extra cost to you.

You have a small black patch on plaster or tile, and the bottle does not match the last article you read. One Dulux page says leave a wash at least an hour. A related trade sheet says 24 hours and do not spray.

Our top picks

Mold Armor Mold Armor FG516 mould blocker 946 ml

Best overall

Mold Armor Mold Armor FG516 mould blocker 946 ml
8.2/10about £25.47
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Professional Strength Professional Strength bleach-free mould remover 500 ml

Best value

Professional Strength Professional Strength bleach-free mould remover 500 ml
8.0/10about £9.99
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Strewth Strewth mould preventer spray 500 ml

Alternative

Strewth Strewth mould preventer spray 500 ml
6.6/10about £14.99
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On this page
  1. 1.Before you spray
  2. 2.Apply, wait, remove
  3. 3.Where our three bottles disagree with a generic method
  4. 4.When to stop

Before you spray

Shut the door to the rest of the house and open a window. GOV.UK's damp and mould guidance says wear a mask, gloves, and goggles, and use a mould and mildew product rather than bleach. If you have asthma, or the patch is more than about one square metre, Healthy Homes says get advice rather than scaling the same wipe across a wall. Children and pets stay out until the surface is dry. Oxford still allows a bleach mould spray on a small area. Where they differ, follow GOV.UK and the label you bought. Do not mix a bleach recipe into a fungicidal wash. Choosing one is the mildew treatment buying guide.

Apply, wait, remove

Wet the growth with the product. Do not scrape or dry-brush it first. Apply only as the label allows. Some trade washes say brush only and do not spray. A trigger bottle is sold to be sprayed. If your tin says brush, do not turn it into a mist because a blog preferred a spray. Leave it for the time that tin prints. Dulux's consumer page for Weathershield Fungicidal Wash says leave it until dry for a minimum of one hour, then rinse so the next coat is not discoloured. The trade multi-surface datasheet says leave 24 hours, brush only, and do not spray. They are not a clock for every amazon.co.uk spray. Rinse when the label says residue will mark paint. Do not rinse a leave-on film.
Mold Armor Mold Armor FG516 mould blocker 946 ml

Testsieger

Mold Armor Mold Armor FG516 mould blocker 946 ml
8.2/10about £25.47
View offer

Where our three bottles disagree with a generic method

The amazon listings in this comparison do not print those Dulux times. Do not invent a one-hour or 24-hour dwell for them. Strewth's bullets say spray on, leave it, and do not wipe. The only UK review says wipe to remove mould, then leave product on. If the bottle says do not wipe, the bullet beats the review. Professional Strength's scrape has no dwell time. One of six UK reviews says wash the mould down before you use the spray. That is a reviewer's order, not a printed minute. The listing marks liquid contents as no, which conflicts with a 500 ml spray, so do not build a method on that row. Mold Armor's fields do not state a leave-on time, and the listing surface is fabric, so a Dulux wall method was never this bottle's instruction.

When to stop

Stop when the patch is about a square metre or larger, when a whole wall or ceiling is involved, or when the work makes you wheeze. None of the three scrapes prints an HSE number, so a large area is a reason to read a wash label in a shop, or to call someone, rather than to guess coverage. A stain that returns in the same cold corner after a clean, dry surface is no longer a bottle problem. That returning stain is bathroom mildew treatment. In England, social housing has its own clocks under Awaab's Law. If you are about to emulsion, do not paint the same day unless the wash label says the wall is ready. Decorating is mildew treatment before painting.

Common questions

Do I wet the mould or scrape it first?
Wet it with the product the label allows. Do not scrape or dry-brush first, and do not vacuum the dust. Oxford City Council and GOV.UK both warn that dry disturbance spreads spores. A damp cloth at the end, if the label allows a wipe, is the removal step.
How long do I leave the product?
Leave it for the time on the bottle you bought. Dulux's consumer Weathershield page says a minimum of one hour, then rinse. A Dulux Trade multi-surface datasheet says 24 hours and brush only. These three scrapes do not print a minute count, so do not copy either Dulux figure onto them.
Do I rinse?
Rinse if the label says leftover wash will discolour the next coat. Do not rinse a leave-on preventer whose bullet says do not wipe. Strewth's bullets say leave it. Its only review wiped. The bullet is the instruction.
What do I wear?
A mask, gloves, and goggles, which is what GOV.UK and RICS both describe. Shut the door and open a window. Keep other people and pets out until the surface is dry. Read the pictogram before you spray above your head.
Can I vacuum the dust afterwards?
No. Vacuuming mould dust blows spores through the machine and back into the room. Oxford City Council says do not brush and do not vacuum. Bag the cloth or wash it. A HEPA claim on a domestic vacuum does not overturn that advice.
What if the bottle says do not wipe and a review says wipe?
Follow the bottle. Strewth's bullets say spray, leave, and do not wipe. The only UK review says wipe for removal and then leave product on. Use the review as one household, not as a rewrite of the label.
When do I stop and call someone?
Stop above about one square metre, on a whole wall or ceiling, if you suspect a leak, or if cleaning sets off asthma. Healthy Homes uses that square-metre line as a point to get advice. RICS sends large areas to a professional. Photograph a returning stain and report it.

Related pages

Mildew treatment comparison

Mildew treatment before painting

Bathroom mildew treatment

Mildew treatment buying guide

Best mildew treatment: which bottle fits your own job

Sources

Public sources from the research digest, last checked on 22 October 2026. Shelf prices and star lines are the amazon.co.uk figures stored on 19 October 2026. The price band is this set, not a market average. No listing was lab-tested.

  1. GOV.UK: damp and mould, health risks for rented housing (retrieved 22 October 2026)
  2. GOV.UK: Awaab’s Law guidance for tenants in social housing (retrieved 22 October 2026)
  3. The Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025 (retrieved 22 October 2026)
  4. GOV.UK: damp and mould in the private rented sector (retrieved 22 October 2026)
  5. Bartoline Fungicidal Wash (retrieved 22 October 2026)
  6. Dulux Weathershield Fungicidal Wash (retrieved 22 October 2026)
  7. Dulux Trade Paint Expert: general FAQs (retrieved 22 October 2026)
  8. Healthy Homes: damp and mould guide (retrieved 22 October 2026)