How To Clean Block Paving With Bleach

Lichen…or those black spots you can see.

Yes, we can remove them, keep reading.

Lichen, the bane of lovely stone. So it's been a nice sunny few days and you thought you would attempt a patio clean yourself, or maybe you have had a professional round to do it for you. The grime, moss & weeds have gone, but wait….What are all those black spots covering the stones? That's what's known as lichen.

For our dedicated video on black stains and their removal, see our YouTube video here https://www.youtube.com/watch?v=K37EdIeBpU4

Black Marks or Lichen, a bad natural stone slab

Black Splodges or Lichen is a Common and Difficult Problem

Lichen

It's known as Lichen (pronounced Ly-Ken) it's a tough little bugger and likes nothing more than to live on your lovely driveway, patio, brickwork, etc.

Actually, it isn't overly fussy where it lays its roots. It is quite partial to sandstone but it will appear pretty much anywhere. It's a type of airborne spore which blows in off trees, settles on your stones and then spreads. It digs itself deep into the stone with root-like structure and is extremely hard to remove.

Your average DIY store pressure washer won't even tickle it, even our 250bar 3600psi petrol powered monster won't remove it. So are those black marks removable, what can you do?

Removal, is it possible? I've really scrubbed it, there must be something I can use?

Yes, there is, but I'm sure you may have tried various methods already. Most things you try the lichen just smirks at you with a "is that the best you've got" attitude.

There are many products out there that remove moss, algae etc but lichen is a different animal. You can spend hundreds of pounds on "dedicated" lichen treatments, but read the reviews, very few live up to the hype.

The photo at the top shows a sandstone patio, which has been freshly jet washed. At least when dirty, it was a uniform mucky colour. Now it's clean it has left behind the black splodges. The problem when cleaning and trying to remove stubborn marks on natural stone is that you can easily damage the stone by using too much pressure. Natural sandstone is very expensive to have laid and after a couple of years, this is what starts to happen.

We recently tried one of those so-called "miracle" products, purely to curb our curiosity. Did it work? Well, kind of yes and kind of no…What do I mean kind of, did it or didn't it.

It was applied as per instructions, down to the letter, on a test area of about 5 sqM. Power washed off and yes it did make an improvement, but was it completely gone, well no! There were quite a few black marks left hanging around even after 15 hours of the product being left to work overnight.

According to the instructions "stubborn areas may need extra treatments" OK you say give it another soaking, BUT…This stuff works out to about £17.50 a litre and we would need approx 16 litres to cover the whole patio. So to give it another soaking just isn't cost effective. Maybe a 2nd dose would have yielded even better results but that would double the price to over £550 for something that could be hit or miss.

An effective and cheap method…Bleach

So anyway, the customer wasn't prepared to spend that kind of money on a chance. To cut a long story short the internet came up trumps and said try some home remedies first, namely household bleach. That night the customer did no more than mix up a sprayer with 3L of Domestos and 1L of water and went about soaking a stone… I didn't know about this until I received a call the next morning saying "wow bleach works well" So here's the after picture of about 15 hrs with 3:1 bleach.

Removing Lichen

Sandstone Tile Treated With Household Bleach

Results speak for themselves

So it's still there admittedly, but this was £1.50 for 2L and it actually worked better. It's a massive improvement and you could do the whole patio once for about £8 and I'm sure a couple of treatments would yield fantastic results.

So give bleach a go first, it may work wonders for some people and do nothing for others. The thing with any product is to follow the instructions. Don't mix chemicals together, and ALWAYS try on a small out of the way test patch first. Just be wary of using with animals around and rinse well after, don't leave it to dry out.

Patience is a virtue, if we get any more luck with other methods we will post them on here.

OK, here's a little update on this. So going on the bleach method we have upped the ante. Welcome to the world of sodium hypochlorite (strong bleach)

Severe lichen

A concrete slab badly infected with lichen

As you can see the Lichen is quite bad. On un-jointed slabs, lichen tends to favour the edges where it remains moist for longer. After reasonable success with household bleach, I decided to go with something a fair bit stronger. Sodium hypochlorite (swimming pool grade bleach) was the way to go.

Word of warning.

So before I continue I'm going to mention safety. Sodium hypochlorite is a lot stronger than bleach, in fact, it's around 3x stronger. Household bleach contains around 4.5-4.8g of sodium hypochlorite per litre or approx 4.5%. Commonly available sodium hypochlorite is normally 14/15%. Care must be taken if you're going to use this product yourself, it will ruin clothes even if the wind blows it. It will also bleach grass and greenery should you spray it on them. It will irritate your skin and can be harmful to your respiratory system if used in confined areas. I don't know what it will do to your hair…I don't have much to worry about. So if you are going to use it, make sure you wear old clothes, gloves, goggles/respirator mask and a hat.

Does it work that well then?

Yes it does, here's the after shot of the above concrete slab.

Lichen removal on patio slab

Removal of lichen

So I left this for 2 hours and worked it with a stiff brush after an hour. I then just rinsed it away with the washer with a wide angle rinse down nozzle. The results as you can see were amazing…

This has become a very popular service of ours, we can chemically clean your patio/driveway should you not want to endure the mess yourself. Just give us a call or drop us an email and we can assess the area and suggest the best course of action. Those annoying black splodges are possible to remove, we can't guarantee 100% removal in 1 application but as you can see its about 95% gone, and the bleach continues to work after rinsing. This method works on all types of stone, concrete, natural stone, block paving, brickwork.

Want to see a wider shot of the patio in question? Here you go, before and after.

Lichen spores on a dirty concrete patio

lichen spores

Removing lichen on a concrete patio

Lichen removal

We made a video on the above concrete patio showing the cleaning/bleaching process. Have a watch to learn more.

https://www.youtube.com/watch?v=SVmm4Npyi-w

We also have some more dedicated videos on lichen removal and general jet washing on our YouTube channel. Please feel free to have a look here

www.youtube.com/dirtydriveaway

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