How much fungicidal wash do I need per m²?

Fungicidal mould wash covers approximately 5 m² per litre for surface mould. For penetrating mould that has gone into the plaster, apply 1.5 times the standard rate. For deep, recurring mould, apply double the standard rate (2 applications). Always allow 24 hours drying time between applications and before repainting.

What is the correct order for treating mould on walls?

The correct treatment sequence is: 1) Scrape off any loose material and wipe away surface mould. 2) Apply fungicidal wash liberally and leave for the recommended dwell time (usually 4-6 hours). 3) Apply a second coat for moderate/deep mould. 4) Once dry, apply steriliser to kill remaining spores. 5) Allow to dry fully (24-48 hours). 6) Apply anti-mould paint as a preventative barrier (2 coats). 7) Address the underlying cause (ventilation, insulation, heating).

Is black mould dangerous to health?

Black mould can pose significant health risks, particularly for people with asthma, allergies, respiratory conditions and weakened immune systems. Mould spores can cause allergic reactions, respiratory irritation, coughing and, in severe cases, lung infections. The HSE (Health and Safety Executive) recommends professional remediation for mould affecting more than 1 m². Children, elderly people and those with existing health conditions are most vulnerable.

What causes mould in UK homes?

Mould requires moisture, warmth and an organic food source (such as plaster, paint or wallpaper) to grow. In UK homes, the main causes are: condensation from poor ventilation (especially in bathrooms, kitchens and bedrooms), inadequate heating (cold surfaces), water leaks (from roofs, plumbing or rainwater penetration), and poor insulation (cold walls and bridges). Condensation is by far the most common cause, responsible for an estimated 80% of mould problems.

Will anti-mould paint stop mould coming back?

Anti-mould paint contains fungicides that inhibit mould growth on the paint surface for typically 5 years. However, it is not a substitute for addressing the underlying cause of mould. If the surface remains damp due to condensation, poor ventilation or water ingress, mould will eventually grow through or around the paint. Anti-mould paint is most effective as part of a combined strategy: treat the mould, improve ventilation and insulation, then apply anti-mould paint as a preventative layer.

Mould Treatment Calculator — How Much Fungicidal Wash Do I Need?

Calculate fungicidal wash, steriliser and anti-mould paint quantities for mould-affected surfaces. Covers walls, ceilings, tiles and grout with severity-based treatment rates.

Affected Area

Total area affected by mould growth

Surface Type

Type of surface with mould

Mould Severity

Determines treatment rate and number of applications

Include anti-mould paint

Add anti-mould paint as a preventative barrier (2 coats at 12 m²/L)

Average Price Per Litre (optional)

Average cost per litre across all products for estimate

How We Calculate This

This calculator determines the quantities of fungicidal wash, steriliser and optional anti-mould paint needed for mould remediation based on the affected area and severity of contamination.

The formulas

Fungicidal wash = (Area ÷ 5) × Severity multiplier
Steriliser = (Area ÷ 3) × Severity multiplier
Anti-mould paint = (Area ÷ 12) × 2 coats

Coverage rates

Fungicidal wash: ~5 m² per litre per application
Surface steriliser: ~3 m² per litre per application
Anti-mould paint: ~12 m² per litre per coat (2 coats recommended)

Severity adjustments

Surface mould: Standard rate (×1.0) — mould on paint surface only
Penetrating mould: ×1.5 rate — mould has penetrated into plaster
Deep / recurring mould: ×2.0 rate — substrate affected, multiple treatments needed

Product sizing

Fungicidal wash and steriliser are available in 500ml, 1L and 5L containers. This calculator rounds up to 5L containers (the most economical trade size). Anti-mould paint is typically sold in 2.5L and 5L tins. Results are rounded up to 2.5L tins.

Health and safety

The HSE recommends wearing gloves, goggles and an FFP2/FFP3 mask when treating mould. Ensure adequate ventilation during treatment. For areas exceeding 1 m² or mould in rented properties, consider professional assessment. Treatment guidance follows HSE Approved Code of Practice and the Housing Health and Safety Rating System (HHSRS).

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Mould Treatment Calculator — How Much Fungicidal Wash Do I Need?

How We Calculate This

The formulas

Coverage rates

Severity adjustments

Product sizing

Health and safety

Frequently Asked Questions

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