Written by Bo Cook
Not All Paving Stones Are Created Equal
Choosing the right paving stone is a crucial aspect of garden design that goes beyond aesthetics. It’s about creating spaces that are beautiful, functional, and also sustainable. And for us, timelessness is key. This topic is especially important for garden designers and landscapers because the choices we make have long-term impacts on the environment, the usability and longevity of the garden, and the overall happiness of our clients. By considering factors such as local geology, climate adaptability, and ethical sourcing, we can create outdoor spaces that not only meet our design vision but also promote sustainability and ensure harmony with the natural surroundings.
When it comes to choosing stone for a project, it’s not just a simple matter of picking out a colour from a tiny 10cm x 10cm sample. It’s much more than matching a “beautiful fossil rich grey stone” that picks out the greyer tones of the Mixed Multi Stock Brick of the house. There’s a lot to think about, and we need to give this the consideration it deserves.
As designers, we’re creating spaces for humans while acknowledging how our designs impact non-humans, and every decision—from sustainability to longevity, suitability to adaptability—has an effect both on and off site.
Here are some aspects I always run through when selecting stone for a project. Yes, there are often compromises, but I make sure to discuss these with my clients, guiding them towards the stone that fits as many of the following criteria as possible so they confident they are making the right choice not just from an aesthetical point of view but also from a sustainable and long-term perspective.
Architecture and Local Vernacular
First off, consider the property’s architecture and local vernacular. Is there a specific stone used in the building or nearby structures? Is it locally sourced and suitable for paving, or just for walling? If you’re dealing with geology like mine—chalk, flint, and soft walling sandstone from nearby quarries—you’ll need to explore other options.
Aesthetics
Stone comes in various finishes—sawn, tumbled, (sawn and then tumbled!) riven, calibrated, reclaimed. The choice should align with the property’s architecture, local area, and design style. For rural gardens on older properties with modern renovations, I often go for tumbled stone or a sedimentary stone cut along its natural bedding plane, married with other natural paving materials and laid in a contemporary way to balance traditional and modern elements.
Local Climate Adaptability
Is the stone suitable for the local climate? The freeze/thaw cycle can wreak havoc on highly porous sedimentary rocks, leading to delamination. Salt can cause surface damage to stone, and UV rays can fade colours – more noticeable on the ‘black’ sedimentary stones.
Slip Resistance Values (SRV)
Check the SRV for dry and wet conditions. These tests aren’t perfect—they don’t account for real-world weathering—but they give a good starting point. Textured stones usually offer better slip resistance, but watch out for increased porosity in these sawn varieties.
Porosity and Stone Finishes
Most commonly used paving stones are sedimentary rocks like limestone and sandstone, with the volcanic and metamorphic varieties being less fashionable. Limestone is finer grained and denser and is generally less porous – although we won’t be including the highly porous Portland Stone in this statement! while the courser grained sandstone can be more porous. Porous stones absorb water faster, reducing surface slipperiness when clean, but they can retain moisture longer and promote algal growth, making them slippery over time.
Location
Is the paving area in full sun or shade? Shaded areas retain moisture longer, increasing the likelihood of algal growth, which makes the stone look dirty and slippery. Stone in full sun can lighten due to the UV radiation, so this is an important consideration.
Heat Absorption and Urban Heat Island Effect
Solar Reflectance Index (SRI) data might not be readily available at the time of writing, but lighter-coloured stones generally reflect more heat than darker ones, which helps mitigate urban heat effects. This is especially important in urban areas where hard surfaces like paving can contribute to higher local temperatures, intensifying the heat. Using lighter stones can help keep outdoor spaces cooler and more comfortable, making them more enjoyable for both people, pets and plants.
Ethical Sourcing
Ensure your suppliers provide clear information about the sourcing and ethical practices of their stone, including labour conditions and the absence of child labour. We avoid using companies that don’t have an ethical practice or Modern Slavery Policy. Look for the Fair Stone certification or if they are on the Ethical Stone Register or part of the Ethical Trading Initiative.
Sustainability
The greenest building is. . . one that is already built.” Carl Elefante. If the paving is fit for purpose, then minor edits may be enough. Reusing stone elsewhere on site is the next best option. Sourcing reclaimed stone is considered more sustainable than sourcing new virgin quarried stone. If it has to be new stone, look for Environmental Performance Certificates and carbon footprint data (kg/m²) from your stone suppliers. Research sustainable practices of quarries to make further informed choices and consider UK stone if budgets allow.
Installation
Can the stone be laid to a flexible or permeable construction that allows for future removal and reuse? Properly installed stone can last for centuries, but tile adhesives and some resin type products can render the future re-use of the stone challenging or completely untenable. Afterlife of the stone is something we should all give thought to.
Cost
Let’s be honest, budget often caps our choices. While local, sustainable, and ethically sourced stone can be pricier, these factors should be weighed against long-term value and environmental impact. Reducing our choices often means we have to compromise on some of the decisions we make, so it is important to determine which are your deal-breakers.
Maintenance
Regular maintenance is key. If you have a reluctant client then choose your stone wisely as one that will get dirty and develop algal build-up quickly will not be the stone for them. Consider adding paving maintenance to garden care packages for clients who prefer not to do it themselves. For those who love getting hands-on every other weekend, ensure the installation can handle the frequent high-pressure cleaning!
By thinking through these factors and discussing them with clients, we can help them make informed, sustainable, and aesthetically exciting choices. The right stone not only enhances the beauty and functionality of a space but also ensures it stands the test of time.
