Which natural stone should I choose for my patio?
We’re often asked by our clients which natural stone is best for a paved area or patio, so we have put together a helpful guide covering the main concerns people raise when researching natural stone paving.
What are the different types of natural stone paving?
The names given to natural stone paving are generally catch-all names for types of stone that share similar properties or were formed in similar ways. For example, sandstone paving is a hugely diverse category with colour and texture varying greatly between different types. Similarly, limestone paving can range from black to almost pure white, but both are still called limestone. Granite too, ranges in colour from jet black to silver; and slate, no longer solely available from Wales, has variations in colour and texture coming from India, China and Brazil.
So, when choosing a stone, first consider the broad properties of the category of stone, and then select a few examples of that type that meet your aesthetic requirements.
What’s the difference between sawn and riven stone paving?
Sawn and riven are two terms that describe how the stone has been cut to make the paving slabs. Sawn stone is (literally) sawn and so has crisp clean lines and is generally flat on all six sides of the paving. This kind of paving is ideal for a sleek and clean contemporary patio and is available in most stone types. (examples on the right in the image below)
Riven paving (on left in above image) is what we think of as a more traditional paving. The edges aren’t exact, straight lines, and the surface is bumpy or textured. This is the most natural looking type of finish as it looks “hewn” from the original rock, rather than machined like sawn paving. Riven paving is most commonly used in traditional garden design schemes and has a timeless and stately feel to it. It can also be used in more contemporary designs, particularly when it is laid in a more modern pattern or shape. Riven paving is generally cheaper than sawn paving.
Will my paving stones be slippery?
Almost all the natural stone slabs on sale will have been slip tested and most suppliers will show details of this on their websites. In essence, the smoother the surface is ground or cut, the more slippery it is. This is a purely physical factor dependent on the type of stone and the way it has been cut and treated.
Some stone types, such as granite, are prone to becoming slippery when cut, so manufacturers often “flame” the stone to give it more texture and improve the grip. This involves heating the stone surface to cause thermal shattering (on a very small scale) which makes the surface a bit rougher and more textured (image below). This is also sometimes done purely to alter the appearance of the stone for aesthetic reasons, and it tends to give a more weathered and “natural” look to the stone.
Whilst the surface texture of the stone is very important in determining how slippery it is, there is also a biological element. As stone gets repeatedly wet and dry (courtesy of our island climate) it provides a surface for algae and lichen to grow on, which can themselves cause the stone to become slippery. How much and how quickly the stone develops this green “biofilm” depends on how slowly the surface dries out between each downpour. Unsurprisingly, stone paving laid in shady areas dries out more slowly and so provides a more conducive substrate for algae to grow on. However, another important factor to consider is the porosity of the stone itself, as this will determine how much water is retained in the top few millimetres of the stone, and hence how long it wakes to dry out. Fortunately, our climate in Cambridge is about the driest in the UK, so this is less of an issue than in many other areas of the country.
How do I stop my paving slabs going green or getting dirty?
Aside from selecting a stone with a low water absorption rating, the most effective method for preventing your patio from going green or dirty is to apply a stone sealer, both when it is first laid, and then every 1 to 2 years – ideally a day or two after having jet washed the patio.
It is also worth flagging up here that most of the commercially available stone cleaning solutions that clean and renew paving contain a mild acid, which cannot be used on some types of stone such as limestone.
Which are the hardest types of natural stone paving?
For most domestic patios the hardness of the stone is unlikely to make a large difference. Short of dropping your anvil collection onto a paving slab, if your patio has been properly laid you should not have issues with the strength of any of the commercially available natural paving stones.
What is the best colour for paving?
Generally speaking, this is a question of taste, and how it fits with the style of your garden. A lighter patio will potentially show dirt more easily, but it will reflect more light so can brighten a dark corner of a garden. Consider how much light a patio will reflect into your house if it is laid outside a window or glass doors as it may provide more light and heat than you bargained for.
More uniform coloured paving tends to give a clean modern look, whilst paving with a wider variety of colours in it can work well in more traditional schemes.
Dark coloured paving can help define a space very effectively, especially when surrounded by lighter coloured paving or edging. This can work very well if you have a large paved area and you wish to define an area for a specific function, such as a dining area. We're blessed with a bright and sunny climate here in Cambridge (relatively speaking!), so dark colours work better here than they do in some of the the more grey and rainy parts of the the UK.
Care should be taken when selecting some dark or black paving such as black limestone, as it will fade under the effects of UV light – sometimes very significantly in as little as 12 months. There are treatments that can be applied to slow the rate of fading, but generally we advise against laying black limestone.
Ultimately though it's and aesthetic choice, and one that your garden designer and landscaper can help you work through.
So, in a nutshell, when choosing your natural stone paving:
Start by considering the garden style you have, and this should enable you to decide between sawn and riven paving.
Next, consider where it will be laid and what tone you want to go for – something lighter and brighter, or darker and more aesthetically weighty.
Having settled on these two main factors, look closely at the categories of stone (sandstone, granite etc) and the individual named varieties on the market.
Finally, cross reference these with the porosity of the stone, and the slab sizes and styles available.
If you’re interested in a new patio or would like to explore garden design options, please don’t hesitate to get in touch with us.