Kedleston's Marble Hall floor, treading on treasure
The floor in Kedleston's Marble Hall dates right back to the 1760s and the current hall’s construction. Finished with Hopton Wood stone, decorated with Italian marble borders and honeysuckle-inspired detailing it is arguably the most significant floor in the possession of the National Trust. Sadly the floor’s condition is deteriorating at an alarming rate and with the floor central to our visitor route we’re faced with a challenge to protect it.
Obviously when the floor was first constructed in the 1760s it wasn't designed to cope with the tens of thousands of visitors a year it sees nowadays. Yet thanks to its incredible craftmanship and engineering it is still structurally sound. However, the extra footfall has taken its toll on its delicate surface and we are seeing an increasing amount of damage.
How is it constructed?
We’ve had numerous investigations carried out by specialists to help us understand the floor's construction and the impact that its current use is having on its future. The decorative marble is set on bricked sections and the Hopton Wood stone rests on a loose sand and lime mixture. This sits on oak boards which are supported by huge timber trusses and joists that span the room. These huge trusses are further supported by 12 cast iron columns seen in Caesars hall below. These columns were added in 1805 by the 2nd Lord Scarsdale after it was noted that the floor was flexing more than anticipated just 40 years after its initial construction.
During the January closed season of 2017 some small problem areas of the floor were lifted to allow unstable stone slabs to be re-bedded to prevent further damage. This provided us with a rare opportunity to examine the floor’s structure beneath the surface.
What is causing the damage?
If you walk around Marble Hall you will probably hear loose sections of stone or marble rattle as they are disturbed. The vibrations of hundreds of footsteps causes the sand and lime to sift out through gaps between the oak boards leaving voids below the stone slabs. With nothing left to support them properly they move and pinch against with their neighbouring slabs resulting in cracking and breakages. Every time you hear one of these loose pieces rattle that is another miniscule piece of irreparable harm occuring.
What investigations have we done?
Back in 1999 we enlisted the help of laser scanning specialists to create an accurate record of floor levels. This process was repeated in 2016 and the comparison of the two surveys confirmed our fears, that the floor is indeed moving. Although it isn’t moving by a huge amount there are signs of continuing movement, which will cause further damage.
Structural Engineers have confirmed that although the floor is structurally sound and safe for our visitors to walk on, it may not be in the floor’s best interests to continue with such high volumes of use.
What are the plans for the future?
In all honesty we don’t know yet and we’re still faced with many possible scenarios, but we do know that we have to make some changes in order to preserve it.
Why not lift it all up and repair it?
Every time we lift a slab we inevitably cause small chips and scrapes so we try not to unless it's absolutely essential. Due to the nature of the design the slabs are very tightly fitted and many would be impossible to lift without trimming their edges and removing historic material. In addition, some of the marble is now so fragile it would certainly break beyond repair rendering it impossible to re-use if we tried to lift it.
Where possible, we try not to remove or replace historic material which would include the lime and sand below the surface. We believe in preserving as much of the original materials as possible when making repairs. We aim to conserve our special places and we believe that removing and replacing large portions of the floor's structure would damage its historical integrity.
Engineers estimate that the combined weight of the floor is over 90 tonnes, that's more than 7 double decker buses! Over the 250 years the supporting beams have adapted to support this huge weight.
If the floor slabs and bedding material were all to be removed the beams could potentially flex back to their original position, altering the angle of the floor. This may make it impossible to relay the slabs into their current configuration as they may no longer fit!
Looking to the future...
Kedleston’s Marble Hall floor is a work of art in its own right and as worthy of protection as the rest of our collection. Although we are yet to decide what the future holds, it’s a treasure that needs to be preserved. The quarries from which the stones came from are now closed making the slabs we have simply irreplaceable, so once the floor is beyond repair it’s gone. For the time being we have cordoned off the central section of the floor to prevent further damage. We find it actually gives you a better view of the floor itself!
We are currently considering options for how we best secure the future of the floor, attempting to minimize further deterioration while still allowing visitors to enjoy the floor.