Welcome to our new blog – this page contains everything you need to know about patio cleaning.

Regardless of the type of patio slabs in your garden, there will come a time when dirt, pollution, algae, lichens and mosses will appear on the surface.

This can leave the surface slippery and looking less than ideal.

While many questionable salespeople will push their “maintenance free” products, the truth is every patio will need at least some maintenance from time to time.

The good news is that it won’t cost you much and with the right chemicals, applied at the right time (usually once a year), you can keep your patio looking pristine all year round.

The Best Patio Cleaner For You

First things first; you need to determine what’s on your patio as different patio cleaner chemicals resolve different issues:

If you have weeds growing through gaps between the slabs, the best chemical to use is Glycosuplahte – this should be applied to the broad leaves of any weeds during the growing season. Take care not to spill this chemical, I always use gloves and a sponge to gently wipe it on the leaves. It only takes a few days for the weed to absorb the chemical, it then reaches the root system and kills off the weed.

For general dirt and pollution that has accumulated on the surface of the patio slab, use a stiff broom and clean the patio with a soapy detergent. This will lift the dirt from the slabs, you can then hose it off with water.

If your patio has black spots (called lichens) or white marks on the surface, then neither a detergent or Glycsuplahte will help, you may even find a powerful pressure washer won’t remove them. You should apply a fungicide such as Benzalkonium Chloride, this chemical will soak into the slab and kill off the lichens, mosses and algae.

Before application

After just one application

Here are the steps I suggest you take:

1. Test the chosen patio cleaner chemicals on an inconspicuous area first and leave for a few good days – some chemicals leave marks on patio slabs so you should check before applying them.
2. Treat any weeds with Glycosuplate applied to the leaves and allow to dry – then leave for a few days.
3. Brush off any loose dirt, leaves and twigs etc from the patio.
4. Use a stiff broom and soapy detergent to lift off any dirt and pollution, wash off with a hose, then allow the patio to fully dry.
5. Last but not least, apply a fungicide such as Benzalkonium Chloride liberally to the surface.

Now Apply a Good Dose of Patience

While the soapy detergent will instantly lift the dirt and pollution, it won’t remove the black spots on the surface, this is actually a lichen, an organism that is similar to a fungus.

Lichens are notoriously difficult to remove and any attempt to aggressively scrape or wire brush them will likely damage the patio as the lichens are very tough and stick to the surface like glue.

A fungicide such as Benzalkonium Chloride will work but it takes time to kill them, and for them to then detach themselves from the patio slab.

For a typical patio, you would need to apply this patio cleaner chemical once per year, ideally in the springtime. If the lichens haven’t detached from the patio by the summer, apply another dose.

I cannot emphasize enough the importance of patience. This chemical will work but it’s not instant.

See the photos further down this page for proof that this chemical works.

What is Benzalkonium Chloride?

Benzalkonium Chloride is used in dozens of patio cleaners, driveway cleaners and moss/algae treatment products that are on sale in the UK.

The truth is, this chemical will kill moss, algae and lichens but it won’t remove dirt, mud or pollution.

BAC 50 Is The Best Product And Here’s Why:

I’ve been using BAC50 to clean patios, driveways and moss on roof tiles for years.

It works and is the strongest and most effective product on the market:

• contains a stronger concentration of Benzalkonium Chloride than any other product on sale
• you can dilute at least 25 parts water to 1 part chemical (works on light lichen growth even with 40-1)
• for use on hard surfaces such as paths, roof tiles, patios etc not grasses
• long lasting effects – sometimes many years
• safe for pets and children once the surface has fully dried
• affordable – currently less than £30
• designed for professional use but anyone can buy it

Buy Now on Amazon

Comparing BAC 50 to Other Popular Lichen/Algae Treatment Products

BAC50 is a very strong product but you don’t need to take my word for it, you can check yourself if you want to:

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 by the name alkyldimethylbenzylammonium chloride.

Similar Products

The only other product that is comparable to BAC 50 is AlgoClear Pro which contains Didecyldimethylammonium chloride at an impressive 40% concentration. This is a professional product and should not be confused with AlgoClear for “amateur” use, which contains the same chemical at a measly 10%.

I prefer BAC 50 as it’s cheaper per litre.  Also, AlgoClear Pro is only sold to tradespeople and businesses.

Is BAC 50 Right For You?

The only reason I prefer this product is that it contains the active chemical at a whopping 50% concentration, I can then dilute it and get hundreds of litres of usable product.

This is ideal for large patios, long driveways and even artificial tennis courts.

£30 worth of BAC50 will last for years.

If you only need to treat a small area OR if you’re not comfortable diluting strong chemicals, then purchase a watered-down product such as Patio Magic.

You can buy Patio Magic on Amazon.

Photos

Here are two photos from a customer who used Patio Magic:

One year after applying Benzalkonium Chloride. Image credit: Telsurrey

Here are the neighbour’s untreated patio slabs:

The neighbour’s untreated patio slabs. Image credit: Telsurrey

Here’s what the reviewer stated in their review of this product:

Had to wait a year before the final black lichen disappeared! Be patient! It really does work! Look at the photos! My neighbour’s path is untreated!

You’ll need to apply these weaker variants more frequently than the BAC50 but as you can see, they still work.

Don’t forget; these fungicides only kill moss, algae and lichens, they won’t “clean” dirt or pollution from the patio. They work best as part of a two-step process where you first clean the slabs with a detergent, allow to dry and then apply a fungicide to kill off the lichens and get rid of the black spots.

And don’t forget the good dose of patience, the person who took those photos had to wait a year for the lichen infestation to detach itself from the slab.

Will Bleach Work as a Patio Cleaner?

You can apply Sodium Hypochlorite instead of Benzalkonium Chloride, it’s a watery bleach that kills off lichen, moss, mould and algae quickly but is harsher and should be tested on a patch area first.

Also, Sodium Hypochlorite should be rinsed off the patio, unlike Benzalkonium Chloride which can be left to dry.

Personally, I’ve found that SH works very quickly but doesn’t have as much staying power as BAC50, meaning you’ll need to apply it more frequently.

Check out the reviews of Sodium Hypochlorite on Amazon.

Which Chemicals Should Never be Used on a Patio?

Brick acid is perhaps one of the most corrosive products you can buy, it’s often advertised as a brick or patio cleaner but is far too abrasive for use on many patio slabs.

I’ve used this chemical to remove hardened cement from hand tools, buckets and shovels. It quite literally dissolves cement and concrete and will eat into the surface of some patio slabs and make them more porous and brittle.

This is definitely one to avoid. It works great at removing cement and mortar but is far too corrosive for most patio slabs.

Why You Should ALWAYS Do a Test Patch First and WAIT For a Few Days

Here is a quote from a dissatisfied customer from Amazon:

Applied as instructions tested on a corner area then applied to my patio and everything was fine untill it rained two days later.It has bleached my £2000 stone patio white.Its ruined.
PLEASE BE AWARE IF USING ON INDIAN STONE.

How Can I Reduce My Patio Maintenance?

Personally, I don’t think brushing a patio with detergent, waiting for it to dry, then spraying it with a fungicide/biocide is a difficult task and it only needs to be done once per year.

But, if you really want to reduce the amount of time spent maintaining the patio, you could seal it with a waterproofer sealer.

This acts as a barrier and also prevents lichen from growing on the surface.

We’ve created a price guide for driveway sealing, it contains links to sites where you can read reviews of the sealer products we recommend.

Explore our driveway sealing guide here.

Conclusion

Patio slabs usually look tired and grubby as a result of pollution, dirt, algae and lichens. Chuck in a few weeds and mosses and you’ve got yourself an untidy mess in the garden.

There are different chemicals and cleaning agents for different dirts and lichens, you’ll probably need to apply more than one to get the best results.

Patience is needed, especially when dealing with lichens which are notoriously difficult to remove.

Patio sealers can help to reduce the maintenance of your patio but they aren’t perfect and may alter the appearance of the surface.

Extra care needs to be taken with certain types of patio, always test a small area first and leave for a week before inspecting it.

Off the shelf patio cleaners are often overpriced and heavily diluted. Other products with a higher concentration of active ingredients can be used, giving you the flexibility to dilute to your requirements.

Don’t want to do this work yourself?

We don’t blame you, that’s why we’ve teamed up with Bark so you can compare quotes from local tradespeople.

The best thing? This service is 100% free to use.

This guide was written by Danny Woodley and was last updated in April 2022.

Don’t forget; we have price guides for hundreds of home improvement projects.

Explore our full list of detailed price guides here.