This is The Best Moss Killer For Patios, Paths and Driveways [Tested]

Are you looking for the most powerful and effective hard surface moss killer you can buy in the United Kingdom?

I spent 17 years working in the construction and home improvement industry and one of the most popular services I offered was a moss removal and treatment service for roofs, paths and patios.

I’ve tried every moss killer chemical on the market and do you know what I found out?

They all contain the same chemicals.

The most popular chemical is called Benzalkonium Chloride (aka alkyldimethylbenzylammonium chloride).

The other is Didecyldimethylammonium Chloride.

They are essentially the same.

Every product on sale in B&Q, every trade store and every website I could find contained one of these chemicals as the active ingredient at various concentrations.

If you want to buy a moss killer that’s affordable and effective at treating moss, algae and lichen, look no further.

I’ve tried them all and this is the most powerful – and I can prove it!

BAC 50 – Moss Killer

  • Stronger concentration than any other product on sale.
  • Dilute at least 25 parts water to 1 part chemical (works on light growth with 40-1).
  • For use on hard surfaces such as paths, roof tiles, patios etc.
  • Long-lasting effects – takes years for moss to grow back.
  • Safe for pets and kids once the surface has dried.
  • Affordable – currently less than £45 for 10 concentrated litres.
  • Designed for professional use but anyone can buy it.

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Comparing BAC 50 to Other Popular Moss Killer Products

You don’t need to take my word for it, you can do your own research if you wish:

BAC50 – 50% concentration of Benzalkonium Chloride (see data sheet here)

Patio Magic (on sale in B&Q) – 7.5% concentration of Benzalkonium Chloride (see data sheet here)

Simply Gone – 9.2% concentration of Didecyldimethylammonium Chloride (see data sheet here)

Ultima Plus XP Moss Killer – 10-20% concentration of Benzalkonium Chloride (see screenshot here)

Don’t forget; Benzalkonium Chloride is also known as alkyldimethylbenzylammonium chloride.

In a nutshell; BAC 50 is the strongest moss killer you can buy and with such a concentrated product, you’ll get hundreds of litres of diluted moss killer solutions to use on patios, paths, and driveways etc.

Similar Products

The only other product that is remotely comparable to BAC 50 is AlgoClear Pro which contains Didecyldimethylammonium chloride at 40% concentration. This is the professional version of their product and should not be confused with AlgoClear for general use, which contains the same ingredient at a measly 10% concentration.

I prefer BAC 50 as it’s cheaper per litre.  Also, AlgoClear Pro is only sold to tradespeople and businesses, if you’re a consumer, you’ll get the 10% version.

Is BAC 50 Really The Best Moss Killer?


I know because I spent several years using this on roof tiles to prevent the moss from growing back after I had physically removed it with a brush/scraper.

Here are some photos I took of my work a few years ago:

Mossy roof

Roof moss removal

Do you see the white and black marks on the tiles?

These are lichens and are very difficult to remove, even powerful pressure washers don’t always shift them.

The good news is that Benzalkonium Chloride will kill them, but it requires some time to take effect.

Keep reading to find out more about lichens and how to best get rid of them.

How Often Should This Chemical be Applied?

I’ve found that the chemical needs to be reapplied every three years to north-facing roofs and every 4-5 years on the sunny south-facing side of the roof.

For patios, driveways and other hard surfaces at ground level, reapply every two years or more often for shaded, damp areas that are prone to excessive moss growth.

The feedback I received from customers was very very positive.

Several of them asked me to come back and treat their patios and driveways, even though I was a roofing contractor.

For patios and other flat surfaces where water may puddle, you may need to reapply more frequently. For particularly stubborn moss, algae and lichen on such surfaces, I suggest applying twice in the first year and then once per year going forward.

How To Apply This (and any) Moss Killer Product

For any surface that is experiencing excessive moss growth (see photos above), first remove as much as you can manually without damaging the surface.

You’ll then need to prepare the chemicals so use gloves and eye goggles for safety.

Because of the high concentration, you should use extra care. This is not a ready-to-use product, it’s highly concentrated and may cause skin irritation.

The following also applies:

  • Do not use if rain is forecast within 24 hours.
  • Keep kids and pets off the area until dry.
  • Do not use it during windy weather.
  • Clean hands thoroughly after use and avoid food or drink when applying chemicals.
  • Do not allow the chemical to enter drains or waterways.

This chemical, like all similar chemicals, is very powerful in high concentrations but becomes inert once allowed to dry.

I used a backpack sprayer for roof applications but for a patio, a watering can will suffice. The chemical is water-soluble so mixes easily.

A dilution rate of 25-1 (25 parts water to 1 part chemical) would produce a very strong product. For light algae growth, a rate of 40-1 could be used.


This product is for hard surfaces only such as roof tiles, patios, driveways and fence panels.

Test on an inconspicuous area first if you’re concerned about discolouration.

This product should not be used on lawns or plants. For grassy areas, try this lawn moss killer instead.

Due to the high levels of concentration, this product is best used for large areas or stubborn moss, algae or lichen growth.

Will This Moss Killer Remove Lichen?

Lichen is an organism that grows on hard surfaces like tiles and patios.

It’s very stubborn and difficult to remove. Even powerful pressure washers struggle to remove this growth.

This and other chemicals of similar strength will kill lichen but it takes time for the dead matter to detach itself from the tile/patio.

Just because the organism is dead, doesn’t mean it will suddenly disappear.

For roof tiles, I’ve found that rainfall and general weathering removes the dead lichen around 1-3 months after applying the chemical.

For patios, it’s the same.

The best way to remove lichen is to use the strongest moss killer chemical you can find and then apply a good dose of patience.

Are Garden Moss Treatment Chemicals Pet Safe?

Most, if not all moss treatment chemicals sold in the UK are safe once the product has dried.

Pets and children should be kept off the treated area until the product has dried.

Choose a suitable time to apply this chemical; avoid windy days and when rain is imminent.

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This guide to the best moss treatment chemicals was written by and was last updated in April 2022.

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Author - Danny Woodley


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