Like all building materials, natural stone will be impacted by changes in environmental conditions (heat, impact and traffic) which is why it’s important to provide stress-relieving movement joints.
When designing a natural stone floor, the following questions will help you deliver a durable scheme and avoid failures in the floor.
Q: Do I need movement joints?
Where the distance between restraining surfaces including perimeter, walls exceeds 2m a perimeter movement joint must be installed. Intermediate movement joints are required where the distance exceeds 10m. With underfloor heating the natural stone flooring should be divided into bays of up to 40m²with a maximum bay length of 8m.
Q: Will the floor be subject to light or heavy loading?
The type of movement joint required is determined by the nature of the ‘traffic load’ that the floor with be exposed to.
Light loading is defined as normal, low-density pedestrian traffic with lightweight, soft wheeled trolleys (e.g. domestic and office locations).
Heavy loadingis defined as high density pedestrian traffic and/or heavy load, static, moving, dropped or dragged areas.
If the floor will be exposed to low loading, or in a low traffic and impact area, a sealant would provide a suitable movement joint. If the floor is in a higher traffic environment a pre-formed movement joint, typically comprising metal side plates with a flexible synthetic rubber core would be suitable.
Q: Is there underfloor heating?
If there is an underfloor heating system, the pipes or cables should be located to ensure that the system is contained within the pattern of the movement joints.
There should also be an assessment undertaken of the likely temperature range that the floor will be exposed to.
Q: Have you taken drying shrinkage into account?
Stone, like all finishing materials, reflects movements arising from supporting substrates. In the early period of a floor’s life cycle, movement occurs primarily from the drying shrinkage of the slab and screed. The Concrete Society indicate that, as a rule of thumb, a typical 10m span slab will experience drying shrinkage of 3.0mm irrespective of design, depth, or amount of reinforcement used.
Q: What colour sealant is best?
As with pointing and grouting materials, because many natural stone absorb, the sealant colour chosen should be similar to the stone to avoid migration of the sealant colour and discolouration of the stone.
For more information on movement joints and natural stone flooring in general, architects, interior designers and clients can purchase a copy of The Code for the Design and Installation of Natural Stone Flooring by emailing enquiries@stonefed.org.uk.
