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The Great British summer has us all thinking about spending more time in our gardens. Unfortunately, the great British winter often leaves our patio looking a little worse for wear. Here is everything you need to know about caring for natural stone in your garden. From jet washing to deep cleaning and a few trade secrets about patio sealing.

What to expect from stone outdoors

Natural stones have been used for patios for centuries. The breathability of the stone as well as the slip resistance and beautiful aesthetics make it perfect for this job.

Sandstone, limestone, granite and slate are all popular choices for patios, terraces and stone features in a garden. However, they are often supplied with little information on what to expect. All of these natural stones are porous. This means that over time, an environment that sees repeated moisture exposure, creates the perfect setting for staining to occur.

Depending on the aspect of the garden and surrounding plant-life, certain issues are unavoidable. Green algae growth is extremely common in areas where water pools, or areas of low sunlight exposure as drying times will increase.

Black spots explained

Black spots are a common sight on sandstone and limestone patios surrounded by trees. These ‘spots’ are not stains as such, but the growth of lichen whose spores originate from tree bark.

Other organic staining comes from decomposition of any plant or animal matter that fall onto the surface

With the correct maintenance regime, natural stone in a garden will last for many years. Even when such staining occurs, it can usually be completely restored back to its original natural beauty.

Patio sealing explained

We have lots of enquiries from clients asking if we can protect their patio from the elements to avoid the discolouration described. As a rule of thumb, we tend to advise against re-sealing outdoor stone and here’s why.

When it comes to stone in your garden, an impregnating sealant will have been applied to the bottom and edges of the tiles before installation. This prevents moisture issues or staining from the installation process.

Further applications of external stone specific sealant to the surface of the stones can help to consolidate sand based jointing compounds and reduce ingrained staining to the stone surfaces from oils and coloured pigments. It is important to note that sealing won’t prevent stone from getting dirty. Algae from forming where the water pools, or lichen spores penetrating into the stone structure. Furthermore, furniture as well as food and drink spillages can cause rust and oil marks that the sealant will not inhibit.

Application of an impregnating sealant can also interfere with a stone’s breathability. This will slow down the rate at which moisture is released back into the atmosphere after precipitation. This can cause further problems such as efflorescence and degradation which would otherwise have been avoided by simply not applying the sealant.

The power of a good deep clean

Unlike our indoor stone treatments, we don’t offer patio sealing as a standard part of our outdoor cleaning treatments. Indoors it is beneficial to prevent the water from penetrating stone. However outside, there is a lot more water and moisture around. This means applying a sealant can cause more problems than it solves. Sealing the stones will reduce the rate of freeze/thaw weathering of the stones, however it does mean that any standing water will create ice on the stone surface when it freezes.

In addition, outdoor sealants can be very expensive, and the longevity can be varied. Our advice is to re-invest the money saved by not sealing your patio into the next 2-3 years worth of professional deep cleaning services.

Our deep cleaning process

Natural stone restoration professionals are able to apply a biocide product before cleaning with fresh water. This will remove the lichen, algae and organic growth from within the stone structure. It will also reduce the slipperiness and bringing back the beauty of the natural product. High powered vacuums are used to remove the sitting water to prevent the dirt from seeping back into the pores of the stone leaving you with a glorious patio once more. Any outdoor sealant will not prevent surface staining from things like oil being dropped onto the stone. However there are specific products that can be used to remove this as part of a deep cleaning process.

In between professional deep cleaning, we advise to simply sweep the leaves regularly from your patio. Following this you should jet wash with a medium to low pressure on a semi-regular basis to keep the stone in great condition. Because the chemical that we use penetrates deep into the stone and kills off the organic matter that was there, this is far more effective in the long-term than jet-washing alone.

 If you do choose to seal your patio

There are occasions when patio sealing can be beneficial, and this is usually when it can help to produce the desired finish for your stone. For slate and granite patios in particular, many clients prefer the deep enriched colour that is produced when the stone is wet. An application of a colour enhancing sealant can create this deep colour. There are breathable sealants that can be used to produce this finish.

It must be added that the colour-enhancing properties of an impregnating sealant will lessen over time. It is therefore advised to reapply this every 2-5 years depending on the patio.

For information on patio cleaning, patio sealing or for any questions on how to care for your outdoor stone please contact us on 01494 438 294 or email

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