One of the most common questions we get asked is “How do I clean my paving slabs?”. Unfortunately, there isn’t a single process for every stone type. Each natural stone differs due to its unique chemical composition and the products you clean it with can have a detrimental effect on the outcome if selected poorly. Location, time, traffic and the type of plants, shrubs and trees that are in close proximity will certainly affect how frequently your paving slabs require cleaning.
Cleaning and Maintaining Your Paving Slabs - Getting Started
As a rule, paving should be swept to remove any debris before beginning the cleaning process. Next, warm, soapy water (pH neutral - NOT containing acid) and a stiff bristled brush can be used to scrub the stone - this method can be used on any natural paving stone, but make sure the bristles aren't too stiff or even made of wire, as this can damage some of the smoother natural stones. A jet washer can be used but we would recommend having this on a low power setting and keeping a reasonable distance from the surface. Softer sandstone especially can loose their colour and vibrancy if power-washed too aggressively or too often.
Before using any product on paving, we recommend testing this on a small area to ensure it does not have a negative effect. Choose an area that doesn't get much foot traffic, or even an off-cut from when the job was completed and test the new cleaning product. Give it a good coat of the product and let it sit for a couple of hours before washing off and checking if there has been any damage or change in the stone.
The most common forms of natural discolouration are moss, algae and lichens - so we will focus on how to best get rid of these on a variety of materials.
Cleaning Sandstone Paving Slabs
The biggest thing to consider when cleaning sandstone is what has caused the discolouration and the porosity of the stone. If the stone is very porous, this requires a lot more attention.
Unsealed/untreated stone can be liable to more discolouration, especially soft sandstones such as Rainbow sandstone. To avoid this in future, once the paving has been cleaned the next time, it would be advisable to add a protective layer of sealant to stop any future discolouration. The hardier sandstones tend to deal with fade and discolouration a little better, so do not need sealing, but it is still an option to maintain that colour.
Do’s:
- Use a diluted bleach mixture. Sodium Hypochlorite is found in bleach and many other cleaning products and this is the component that kills most moss and algae. Use this with caution and be sure to test in on an inconspicuous area first to ensure it does not cause a reaction. Bleaching can lighten the colour of the paving, so please make sure you check first.
- Follow the manufacturer’s guides when using any sandstone specific cleaning products.
Don’ts:
- Do not use any cleaning product containing iron as this can react with the stone and could cause a rust colouration to the surface. A lot of products labelled as 'Moss Killers' contain the substance that can destroy moss well and truly, but can also discolour and rust your paving. The substance known as 'Ferrous Sulphate' can be called Iron for all intents and purposes should be avoided at all costs.
Cleaning Limestone Paving Slabs
Limestone can be challenging to remove stains as a lot of the common stain removers are not suitable for this material as they contain acid. This is because the geological make up of limestone contains a lot of calcium and other carbon-based material, which reacts terribly with acidic materials – completely ruining your stone.
Do’s:
- If using a pH neutral detergent and water fails, a very mild bleach (100ml:4L of water) solution will be enough. Use this with caution and be sure to test in on an inconspicuous area first to ensure it does not cause a reaction. Bleaching can lighten the colour of the paving.
- If a stronger stain or cement remover is required, it is imperative to check it is suitable for limestone (these are usually alkaline based, so perfectly suitable).
Don’ts:
- Under no circumstances should an acid-based product be used on limestone paving, whether this be natural (lemon juice/vinegar) or man-made. The chemical reaction between the two can permanently discolour the surface.
For more information, visit our how to clean limestone paving guide
Cleaning Slate Paving Slabs
Generally, slate is very robust and maintains its colours much better than a sandstone or limestone paving, so it should clean up much better. Simply follow the instructions at the top of the article and you should see good results each time you do it.
Once your slate has been installed, it is important to give it a good pressure wash as the layered characteristics of slate mean the top surface can flake. A higher quality slate will stabilise and stop flaking after the first few washes.
Do’s:
- Use a floor cleaner (pH Neutral) and water only.
- Use a specialist slate cleaning product.
- For tougher stains you can use a very mild bleach (100ml:4 litres of water) solution.
Don’ts:
- Use a wire brush as slate can be susceptible to scratching.
Cleaning Granite Paving Slabs
Granite is naturally a highly durable material for paving, but it can still be affected by weathering and usage.
Overall granite is going to survive brutal weather and conditions without much of an issue, but it is important to give it a spruce up every now and again.
Do’s:
- Use a pressure washer. Often, it’s just the surface that requires dirt removing.
- Use specific solutions formulated for use on stains with granite.
Don’ts:
- Do not use an acid-based solution.
- Do not use bleach.
Sealing Your Paving Slabs - Additional Info
It is imperative when using chemicals that you wear your recommended protective clothing such as gloves, goggles, boots and overalls.
Prevention is certainly better than cure so by sealing your stone (see "Do You Need To Seal Stone Paving") and regularly sweeping your paving slabs will help reduce the chance of any debris staining them
It's important to note that there is no ultimate prevention for keeping your paving clean - if you ever discovered one, you could make millions! There are ways to keep on top of it, but as with any outdoor activity it's going to get messy eventually. A nice metaphor for life itself, hey!
When cleaning or maintaining your paving slabs, there are so many options for cleaning products, but the important thing to do is test, test, test! Most are suitable for use on most types of paving, but it's important to read labels and test a small area before committing to using it across the entire patio. The last thing you want to do is ruin your paving for good - so exercising a little caution goes a long way.
