The first choice is chemical-free or biocide, and it usually comes down to what is nearby rather than the surface itself: pets, ponds, plants and children change the right answer more than whether you are treating a patio or a roof.

Chemical-free, or an HSE-approved biocide?

MossOff Multi Surface Moss & Algae Killer is a non-biocide formula: it does not rely on the biocidal actives used in the other two products, dries to an invisible biodegradable coating, and is safe to use around pets, children, plants and posts. It suits tarmac, patios, driveways, decking, fences, roofs, astro-turf and walls, with visible results in 7 to 10 days.

Where the growth is heavier, or the surface has been fighting mould and algae for years, an HSE-approved biocide works faster and lasts longer. MMC-Pro (HSE 7824) is a pH-neutral, bleach-free and acid-free concentrate that kills green mould and algae in 2 to 4 days and generally prevents regrowth for around 9 months on an exposed surface. N-Virol covers similar ground and doubles as an approved wood preservative, which makes it a common choice for treated timber and decking as well as stone. It is also listed by Natural England as suitable for use in and around bat roosts, useful to know on sites where that matters.

Both MMC-Pro and N-Virol are regulated under the Control of Pesticides Regulations. Always read and follow the product label before use, and keep pets and anyone unprotected off the treated surface until it has fully dried.

Match the dilution to how bad the growth is

N-Virol’s label gives three dilution rates depending on severity: 1:19 for normal growth, treating up to 500m² per 5 litre pack; 1:9 for heavy growth, treating up to 250m²; and 1:4 for severe growth, treating up to 125m². Where moss has built up thickly, breaking the surface first with a stiff brush improves how well the solution penetrates. MMC-Pro is applied at a standard rate of 4 to 5m² per litre of diluted product with a knapsack sprayer, onto a dry surface, and left for 3 to 5 hours to work.

Which product for which job

Family patio or driveway with pets and children around: MossOff Multi Surface. Heavily fouled block paving, roof or path that needs a longer-lasting result: MMC-Pro. Gravestones, timber decking or anywhere you also want a wood preservative: N-Virol.

All three are concentrates diluted before use, so the pack size you need depends on the area and how bad the growth is. If you are not sure which dilution rate applies, the technical sales team can talk you through the label before you buy.

Frequently asked questions

Will these harm my plants, pets or fish pond?

MossOff Multi Surface is a non-biocide formula and is safe around pets, children and plants once applied as directed. MMC-Pro and N-Virol are HSE-approved biocides: both ask that contact with plant life be minimised, and MMC-Pro's label notes that light run-off onto grass, soil or hardy plants will not normally cause damage, though heavier over-spray should be flooded with fresh water. Always read the product label before use, and keep pets and unprotected people off the treated surface until it has dried.

How long before I see results, and how long does treatment last?

Expect visible change within 2 to 10 days depending on the product and the growth involved. MossOff Multi Surface shows results in 7 to 10 days; MMC-Pro and N-Virol typically kill green mould and algae in 2 to 4 days, with black mould and lichen taking longer. Regrowth prevention runs to roughly 9 months for MMC-Pro on an exposed, south-facing surface, and up to 500m² of light cover from a single 5 litre pack of N-Virol at the lowest dilution.

Do I need to pressure wash first?

No, and doing so can work against these treatments. All three are designed to be applied to the existing growth by sprayer, left to work, and allowed to die back and weather away naturally. Heavy, established moss can be broken up or brushed first to help the treatment penetrate, but pressure washing beforehand strips away the growth the product needs to act on.