Old stone floors should be cherished and, wherever possible, retained, as unnecessary replacement will harm a building’s character and possibly its value.
Durable local stone of various sorts was used historically as slabs or finer tiles for flooring. Cobbles or ‘pitched’ floors, comprising small pieces of stone set on edge which were able to withstand much wear, were frequently laid in ancillary areas, such as kitchens and outbuildings.
Decorative schemes with stones of contrasting colour, including imported marble, became popular from the 17th century. Many period properties still retain this original feature, and it is one that will likely last forever with some proper maintenance.
Don’t lift original stone floors
Old stone floors were laid on well-rammed earth or chalk, sometimes with a bed of sand or lime mortar. If you have concerns about damp, it’s generally inadvisable to lay a plastic damp-proof membrane (DPM) on top of new concrete beneath the stones because their ability to ‘breathe’ will be impaired, displacing moisture into the bases of previously dry adjacent walls. Instead, if a floor is genuinely damp, consult a builder with experience in old house conservation.
It’s very easy to spoil flooring by re-laying it, so only attempt this if there’s little alternative. When installing new heating pipes, make sure that you employ a competent builder to do the lifting with great care rather than leaving this responsibility to plumbers. Lifting and entirely re-laying an old floor to install underfloor heating or incorporate insulation is not generally recommended.
Repairing original stone floors
Undulations add interest to old floors so, unless dangerous, they are best left. Dangerously uneven or rocking stones can be rebedded in coarse sand or hydraulic lime mortar, although slight undulations might be reduced with simple matting.
Flaking stones can be dressed back to remove loose material, although laminations in limestone can in some cases be repaired by conservators using injections of lime-based grout. With serious erosion, it may be possible to lift and reverse stones.
Deep holes or chipped edges in stone flooring can be filled with a hydraulic lime mortar, but continuing maintenance is likely to be necessary. Strong cementitious mortar or waterproof grouts that inhibit ‘breathability’ – preventing moisture from passing through permeable materials – are not recommended. Renewing part of a damaged stone with matching new material is normally preferable to complete replacement.
Maintaining original stone floors
Where needed, joints between stones or cracks across them can be pointed with a hydraulic lime mortar. If joints have never been filled or are dry-jointed with sand, repointing with lime is not necessarily required.
Old stone floors usually only require regular sweeping or vacuuming and occasional washing with minimal quantities of water (possibly with pH-neutral soap). Stains frequently respond to a 50:50 water to white spirit solution or specialist poulticing. The sparing use of microcrystalline wax is sometimes appropriate to protect surfaces or reduce powdering. ‘Breathable’ floor coverings (natural fibre or rush matting) can provide added protection. Avoid harsh cleaning agents and impermeable sealants.
Replacing stone flooring
Where a floor is relaid or replaced, a damp-proof membrane should normally be omitted in an old building (pre-dating circa 1919), as it prevents the floor from breathing and risks increasing dampness in walls. Instead, try using a breathable construction, such as limecrete beneath flagstones pointed with lime mortar.
A short history
Local stone of various types has been used historically in many parts of the UK for stone floors. Flagstones are produced from hard, dense and durable stone that can be readily split along the bedding plane (the surface separating rock strata). Although generally riven (split), some stones are sawn or dressed. Stone types include a wide range of sandstones, hard limestones, granites – mainly sawn and used from the 19th century – and other igneous rocks.
Historically, stone flooring was laid mainly on the ground floor or at cellar level. Overall sizes tended to be up to one metre square, but smaller slabs were more economical and easier to lay, and thickness varied according to the type of stone. Before the 1800s, stone flooring was laid on compacted earth or chalk, sometimes with a bed of sand or lime mortar. Joints between stones were filled with lime mortar or left open.
For information on all aspects to do with the care and repair of old buildings contact the Society for the Protection of Ancient Buildings (SPAB). It operates a technical helpline, runs weekend courses and produces advisory publications.