FOOTPRINT+ 2024: Stone Bricks

No frog, no problem

One of the presentations I attended during FOOTPRINT+ was trying to redefine construction norms and explained how stone bricks could be used as a low carbon alternative to their clay counterparts.

Marcus Paine (Hutton Stone) and Michael Poultney (Albion Stone) gave a fascinating presentation on how Portland Stone is mined and generates large stockpiles of whitbed, which sit unwanted… although things are changing and this is now being used to create stone bricks.

Joe Chilvers (Adam Richards Architects) also told the audience how he teamed up with Valérie Bergeron (Polycor) to specify their French Massangis limestone brick on the Mayfield School in Sussex.

Portland Stone

Apparently there is 25,000 cubic metres of Whitbed stone in stockpiles at Albion Stone’s mine, but why? Well this is essentially a waste (“un-loved”) product, generated because although the sales of Portland stone are around 50/50 Whitbed/Basebed, the depth of the Whitbed is around twice that of the Basebed. So when mining the full depth of the combined bed, about a third (half the Whitbed) isn’t sold and is stockpiled.

There’s nothing wrong with this stone. If anyone reading has ever specified Portland stone for a project, you will know that the selection can be meticulous, assessing various samples to guide the supplier as to what is (or is not) acceptable. The message coming through loud and clear was that our industry has slightly lost sight of why we used stone and how we should use it. Examples such as St Pauls Cathedral show us that all parts of the stone bed were used for a variety of reasons such as cost/resource efficiency, varying performance and also to create natural interest and differentiation across the facade, floor or place of use. Nowadays, stone with shells, small blemishes and minor colour variances are often rejected, with the aim of creating a near perfect array of pieces.

And this is where stone bricks come in. The rejected, unloved stone can be cut into bricks, offering a great solution which mixes up those imperfections into a mosaic of details and colours - it’s a nod back to the more efficient ways of using everything from days gone by.

Stone Bricks

Michael told us how mother nature has been designing these brick for over 140 million years and every one is unique. The relatively simple cutting that is required on their new brick production line leads to a competitive price, especially considering the low carbon nature of the product. 

You can find some useful info on the bricks here, but below is some key info:

• Compressive strength of 40 to 60MPa (upper end of masonry bricks and approaching engineering bricks)

• Installed just like normal bricks - same size as metric size bricks (215mm x 102mm x 65mm)

• More stable material, therefore less movement joints

• Good fire resistance

• No risk of efflorescence

• Can use a cement mortar (or lime for lower carbon)

• Lack of a frog is not an issue. No frog, no problem

• c£2.50 per brick, but comes down if you include specials and bespoke sizes which are easier to produce from stone and actually offer some nice architectural solutions.

I’m not sure how true this is, but Michael said that they can fulfil orders almost immediately. There must surely be a throughput limit to the new facility at Albion, but I suppose the point is that there is plenty of stockpiled material and currently low demand for this ‘new product’

Mayfield School

Joe told us about the design of the Mayfield school and how they switched to a stone brick once they stumbled across Valérie and Polycor and learned about their available limestone brick. Working with Polycor they specified a double length brick to feature in a unique bond design (which has less cuts per square meter of wall) and learned how the performance of the stone brick either matches most clay bricks or exceeds them, meaning little to no extra work to make the swap.

Joe couldn’t have been more positive about using the bricks, explaining that “Dave the brickie” quickly got on board too once he realised there was little difference in the laying.

Next time you are looking at using bricks, why not consider stone bricks as a low carbon alternative.