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How to remove black spot from sandstone patios and pavers

how to remove black spot: a how to guide

What’s the best way to get rid of stubborn black spot?

We would recommend using Black Spot Remover Plus to remove black spot from sandstone patios. It is a concentrated cleaning solution specifically developed for the removal of black spot lichen.

This product has many 5 star reviews on Trustpilot & Amazon and has been warmly received by our customers.

If you wish to view the product pages for more information and prices please click on the product titles highlighted in blue. You can also view all products on our website page

Floorseal Black Spot Remover Plus is suitable for removing black spot lichens from natural stone, brick, concrete and block pavers. To carry out lichen removal from a patio, you simply need dwell time and agitation to achieve optimal results.

Black spot lichens which have formed on Indian sandstone, York sandstone and concrete can be particularly difficult to remove. They are highly resistant to pressure washing, therefore, a cleaning agent is always required.

Please carry out a test patch to assess the dwell time required to remove the black spot on your patio. Each patio will be different, some black spots may have only recently formed and be quite mild. On other patios, the black spot may have taken 20 years to form. The dwell time required is obviously going to be different for those differing scenarios.

Typically the most severe infestations of black spot are found on concrete, York sandstone & Indian sandstone. The products featured within this article can be used on sandstone, other natural stone, block pavers and concrete.

What is black spot?

Black spot on a sandstone patio.

It’s a lichen that looks like a spot or smudge, basically black marks in various sizes. It is a living organism which inhabits the surface of garden stonework, this can be on both floors and walls.

Black spot on sandstone tends to be more difficult to remove than black spot on block pavers. We think it is the most difficult to remove when growing on concrete, but never impossible.

Why do you recommend carrying out a test patch?

Carrying out a test patch will give you the correct timing required to remove the level of black spot contamination on your patio. A thick or concentrated build-up of black spot is going to require both more effort, time and product than light contamination.

If you carry out a test patch you will know how long the product will take to work for you. It may be necessary, on an extremely heavy build-up to repeat the process. Or you may just need to spray back over the odd patch when most of the surface has been cleared.

All the information gained from carrying out a test patch is important. Do not guess the dwell time or you may waste product.

For light contamination of patio black spot, you may only need 20-30 minutes of dwell time. There will always be large variations in dwell time. Black spot removal is unlike the removal of green algaes and moss. The chemicals that are used for those problems are totally different. They are products which are just sprayed on dry and left to soak in and then dry out again.

Why use our Black Spot Remover Plus?

Before and after black spot removal.

Floorseal Black Spot Remover Plus is a full-strength cleaning solution which is to be used neat. It has a high level of active content; this reduces the dwell time required to remove lichens. You will still need reasonable dwell times on medium to heavy contaminations.

Using general patio cleaners means using more product and leads to a less than satisfactory result. Sometimes people will try to use general moss and algae removers which have no real effect on lichens.

Use the correct product at high strength, couple this with some patience and you will get great results every time.

The best method of application

The following information will explain how to get rid of black spot on Indian sandstone and other external surfaces. If you have struggled with weaker ineffective products, this application procedure will work in conjunction with our product.

Use old clothes and appropriate PPE.

Pre-wet your patio with a hosepipe so the surface fully absorbs the water leaving it damp. If you think the overspray, or run-off, will affect adjacent plants and lawns use more clean water to wet these areas out.

Do not allow the product to run into ponds or encounter fish or other aquatic life.

Use the product neat – do not dilute!

Apply Black Spot Remover Plus with a pump-up sprayer or watering can (make sure you rinse out the sprayer or watering can afterwards).

Flood the surface, the surface of your patio should be visibly wet. Make sure you spread the black spot remover over the surface and then leave it to dwell. As an average, we recommend at least an hour (or adjust to suit local conditions). 2 hours + is not uncommon.

Periodically agitate the surface with a stiff brush. The joints or pointing will usually start to dry out more rapidly than the face of the slabs. Pay attention to all areas and make sure the surface does not dry out during this dwell time. Do this by adding more product. The agitation with a brush is simply that; it is not to physically remove the lichen it is just to keep the surface entirely wet.

After at least 1 hour (or more depending on local conditions) rinse the product away with clean water. Only do this if the black spot has gone. If it is still there extend the process or repeat.

For best results, after rinsing off the surface with a hosepipe, pressure wash the patio. Some people like to pressure wash the surface before and after treatment.

If you struggle with the removal of black spot

If someone struggles with black spot removal it is generally for the same reasons. The information below explains the reasons why the process could become frustrating and appears difficult.

You did not use enough product, measure the area to be treated in square metres. Do it accurately, do not guess! Flood the surface with product so it is wet, just slightly damp is not wet enough.

This product is not a general-purpose weed killer that is sprayed on and left to dry. If you use this product, or assume you use it like a weed killer this process will fail. This is a contact product that needs to be kept wet. Do not let the surface dry out,  keep it wet and use a long dwell time.

Do not overwet the surface with just clean water during a very long dwell time. You will need to use more product to keep the surface wet during the dwell time. Misting clean water is fine for lighter contaminations but still not ideal. Using a 50/50 concentration with water would be better than just adding more water.

After a dwell time of around an hour, if some black spot is still there, extend the dwell time. Just rinsing all the product off the patio means you will need to follow the process again. Extending dwell times can mean using a lot less product than repeating the process.

You could go back to treat small areas (or odd spots) by spraying the black spot remover onto the surface when it is dry. This will slightly accelerate the process, but you do use more product.

Work in small sections rather than taking on large areas. If you have the odd area with black spot on after treatment spray over them individually. You can go back to these areas whilst working on another area

People working on too large an area make up the greatest proportion of people who struggle with black spot removal. This is basically due to rushing and often not carrying out a test patch. Create enough time in your diary to do the job, it can be time-consuming.

Do not confuse other contaminations for black spot. York sandstone is notorious for having a huge cross-section of contaminants on its surface. York flags are often very old and may have been uplifted and moved around. They often have heavy general staining and bitumen on them. A test patch will tell you whether you are dealing with an organic infestation or not.

To give your Black Spot Remover a helping hand, or if you wish to clean vertical surfaces you can use Cleaner Additive. This product is a thickening agent which is added to the Black Spot Remover. Cleaner Additive is very useful when cleaning really porous sandstones & concretes which dry rapidly. The additive prevents the remover from drying as quickly by keeping the product on the surface, thus slowing the drying process.

Cleaner additive is also highly effective when used in conjunction with our Black Spot Remover, for cleaning vertical surfaces like walls and lintels. The Black Spot Remover will cling to the surface it is applied to more easily when mixed with the Cleaner Additive.

As a bonus, Cleaner Additive slightly foams so you can see where the remover has been applied to after the surface has been pre-wetted with water.

Available Sizes

Black Spot Remover Plus is available in a 5 litre & a larger economic 20 litre container.

Black Spot Remover (5L and 20L formats)


Adapt these figures by carrying out a test patch, as a general guide 1 litre covers no more than 4m2-5m2. Do not exceed the figures below.

A 5 litre container covers 20m2 possibly up to 25m2.

A 20 litre container covers 80m2 possibly up to 100m2.

Sealing patios and preventing black spot returning

We recommend sealing by using Floorseal Indian Sandstone Sealer & Colour Intensifier. It is a breathable sealer which waterproofs and also highlights colour in a subtle and natural way. We have a variety of sealers, contact us for details.

Sealers will inhibit the growth of anything organic as it waterproofs stone. In addition to this many sealers will highlight natural colour contained within the stone.


Floorseal Green Remover Concentrate –This product can be applied to remove moss. But can also be used a follow up treatment after removing black spot lichen with Black Spot Remover Plus. Green Remover Concentrate can be applied as a preventative measure. It does not remove black spot but prevents its return, as well inhibiting the growth of moss & algae. Simply spray onto dry stone, after the black spot has been removed. It can be sprayed onto sealed surfaces on an annual basis.

Floorseal Green Remover Concentrate has a residual effect, it can be applied once or twice a year. Typically in the spring, after power washing the patio and again in the Autumn if required. A North facing patio laid under trees, coupled with poor drainage, is more likely to suffer from organic growth than a south facing patio.


Further information


Please Click Here to view our products & accessories for cleaning and sealing sandstone. This also includes all of our handy ‘how to’ guides for cleaning and sealing interior or exterior sandstone.

The information contained within this article is not exhaustive. If you need further information please contact Floorseal on (01484) 861461 or email us our web address is