How to remove black spots on a patio


So you have black spots, also known as lichen, on your patio and you want to know how to get rid of those horrible marks but just don’t know how! Laying paving and offering jet washing services for my garden maintenance and landscaping business, I am often turning up at a potential customer’s home to discuss the removal of black spot ridden paving slabs with a view of laying new ones. But is this necessary? I have all of the answers right here on how to remove black spots from your patio!

What are the black spots on my patio?

Black spot is also known as Lichen, which is actually an organism thriving in damp conditions that first shows as tiny dots on untreated porous paving slabs, growing to much larger, noticeable, hard to remove stains after just 2-3 years of having your new patio laid!

Although not impossible, Lichen or black spot don’t like to attach themselves to concrete patios, but instead prefer to latch onto natural paving slabs such as imported sandstone, since they are much more penetrable compared to concrete. But why does it matter how penetrable your patio slabs are you ask? Well this is because, as black spot matures, it sends out tendrils into the pores seeking for nutrients, much easier to find in mineral stones. It’s also worth noting that the more cement you have in your concrete paving slabs, the less likely you are to have black spot. But then, natural paving is much more decorative with each patio slab having a unique pattern.

How do I remove black spots from my patio?

There are 2 real options when it comes to removing lichen from your patio, and that’s the use of a domestic or commercial jet wash, as well as the use of chemicals. Below I will discuss the use of a jet wash compared to the use of chemicals, and if any of the 2 can actually remove black spot from your patio! Unlike a lot of other websites giving advice on how to remove black spots from your patio slabs and simply research and re-type the information, I have came face to face with lichen many, many times! I will be speaking from real experience!


Will jet washing my paving slabs remove the lichen from my patio?

The answer to this question, is that it depends. How long have you had black spot on your patio? Remembering that they start to show after 2-3 years of newly laid slabs, any lichen at 3-4 years of age or younger should be able to be removed with a domestic pressure washer. Of course, this isn’t given in every case, but you should at least be able to remove the majority of black spots on your patio with a domestic jetwasher.

Any lichen older than 3-4 years of age will be much harder to remove, as they have now became real hard to remove stains! If you’ve no idea how long your paving has had black spots and your pressure jet washer has removed some, but not all of the black spots, then a more powerful pressure washer should be able to finish the job off.

It’s important to know that pressure washers have a wide range of power ratings which is usually shown as BAR. Lets take a look at domestic Karcher range of pressure jet washers for example;

  • Karcher K1 (90 bar or 300 litres per hour)
  • Karcher K2 (100 bar or 342 litres per hour)
  • Karcher K3 (120 bar or 380 litres per hour)
  • Karcher K4 (130 bar or 420 litres per hour)
  • Karcher K5 (145 bar or 500 litres per hour)

These prices range anywhere from the £50 mark to the £200 mark depending on where you shop, but bare in mind that you really can tell the different when it comes to the pressure rating of your jetwasher and black spot removal. It also works best for me when using the dirt blaster attachment as this seems much more powerful compared to the floor cleaning attachment. I personally use the Karcher K4 which cost me around £150 6 months ago, and if that doesn’t remove the black spots from your patio, then I don’t think the K5 will have much more luck.

Always be careful when using a pressure jet washer to remove the black spots or lichen on your patio slabs as you can easily dislodge and remove the pointing (cement between each slab). Although this is an easy repair for anyone hands on. It’s also good practice to spray a cleaning detergent on your patio before you start pressure washing to help remove the lichen stains.

Here is an example of me using a very powerful petrol jetwasher for a better chance of removing black spots from a customer’s patio. You can see by the video that if I focus the gun in one area, the stains will be removed. But by giving it the once over, replicating a less powerful pressure jet washer, the stains remain. Of course, even this pressure washer doesn’t remove all stains and very much depends on how mature they are!

Will chemicals remove lichen from my patio? Does black spot remover work?

The answer to this question is that depending on which chemical you use, and depending on how long your patio has had black spot, is that it will work, but maybe not the first time round! Although not recommended by everyone due to fear of damaging your paving, the first chemical that I would use is bleach as this is much cheaper than products specifically designed to target black spot (lichen) and I personally, have never had any problems using it. Just be sure to avoid using thick bleaches as this can cause other spots, even harder to remove than the lichen your already trying to remove from your patio.

  1. First dilute your bleach with a 10:1 ratio with clean water and slowly work your way up to 2:1 if absolutely necessary. The ratio will need adjusting depending on how matured your black spot is, although multiple attempts may still be necessary, fading the lichen more upon each treatment.
  2. Black spots send tendrils into the paws of your paving slabs before showing on the surface, be sure to treat all of your paving slabs even if they look clear from black spot.
  3. Wet the surface of your patio before applying the diluted bleach and be sure to keep wet until you rinse off with clean water. Avoid rinsing off onto plants and grass.
  4. Although hard work, try using a wire brush whilst the bleach is applied as this will help eat into the black spots and leave 1-2 days before treating again.
  5. If you have a jet wash to hand, try using this between treatments, but after the bleach has been washed off with clean water, to avoid getting it in your eyes, plants etc..
  6. Always use safety equipment such as gloves and goggles as well as remembering that bleach stains clothes!

Other products that I have used include chemicals purchased online that are specifically designed to kill off and remove lichen stains. These products include ‘black spot patio remover’ at £39.99 for a 2 litre bottle, and ‘Smartseal patio clean Xtreme’ at £36.95 for 5 litres from Amazon, although prices may have changed at the time of writing this post.

The ‘black spot patio remover’ allows you to spray or pour the chemical directly onto the patio with no need to dilute, allowing it to sit for 20-30 minutes before washing off, whilst the ‘patio clean xtreme’ needs to be diluted on with a 1:1 ratio and keeping it wet for 1 hour before washing off. Be careful when purchasing other patio cleaners and most of them aren’t aimed at removing black spots, and remember that patio sealer is a completely different product.

On one of my most recent jetwashing jobs, I had very stubborn lichen stains to remove from a customer’s patio, and offered 4 treatments to try and remove the stains. I actually used both of these black spot removers upon each treatment, and although they work well, in my personal opinion, neither showed better results than the other and 4 treatments were needed (5 including bleach) over a 10 day period to provide satisfactory results. Could the bleach have removed the stains over 5 treatments? I’m unsure! But given time, chemicals will work!


How to avoid getting black spots on your patio

The best way to remove black spots (lichen) from your patio is to not get them in the first place! If you have finally got rid of your black spots, or you have a freshly laid patio, be sure to protect it using a patio sealer. These are inexpensive to purchase, much cheaper than chemicals designed to remove lichen, and will seal and protect your patio against grease, dirt, oil, prevents weather damage and stop the lichen from sending tendrils into the pores in search of nutrients by sealing them.

Most patio sealers will recommend repeating the process every 1-2 years to keep your paving slabs healthy all year round, but I would recommend doing this yearly to be safe. Sealing your patio is very easy, with most sealers being able to simply be rolled on and left to dry. Remember, it’s a lot cheaper to maintain your patio, than it is to replace it!

Please share your questions below as well as your own remedies! I am always keen to help others, as well as learn new ways to remove these awful black spots!

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