The facing of vertical, and occasionally horizontal, surfaces can be carried out in two basic ways. The first, and the most often associated with ceramic tiles, is by adhering relatively small and thin units straight onto the surface of the wall.
Alternatively, where larger modules are specified the panels are generally thicker and require to be mechanically restrained to the structure. Stones in the collection can be supplied in small tile formats which are fixed in the same way, or alternatively in larger modules secured by proprietary steel fixings.
STONE CLADDING
Vertical stonework can be divided into two groups: The first is masonry requiring blocks of more than 90mm width on plan, laid as either a solid load bearing wall or as a non-load bearing facing to a cavity wall. The other is cladding, that is panels of relatively large face area carrying no load other than their own weight and mechanically fixed to the structure.
Cladding can also be subdivided. The first group constitutes natural stones requiring a thickness of 50mm or more to retain their structural integrity e.g. sandstones and most limestones. The second contains stone which can be used in thin panels and tiles e.g. granites, marbles, travertines, hard limestones and slates. Basic thickness requirements for cladding in these groups as outlined in BS 8298: 1994 are as follows:
| General Use |
Minimum stone Thickness |
Specific Location |
| |
Limestones
& Sandstones |
Hard Limestones & Other stones |
|
| External Cladding |
50mm |
20mm |
Less than 3.7m above the ground/floor level and continuously supported. |
| |
50mm |
30mm |
Fascias less than 3.7m above ground/floor level, cills, copings and supported reveals. |
| |
75mm |
40mm |
All other locations. |
All other locations
Internal Linings |
50mm |
20mm |
Less than 7m above ground/floor level and continuously supported. |
| |
50mm |
30mm |
All other locations
except soffits. |
| |
75mm |
40mm |
All soffits including
inclined soffits. |
FIXING SYSTEMS
The main objective of any fixing system is to achieve a safe and reliable connection between the cladding and the structure, whilst building in sufficient design clearance to accommodate all anticipated tolerances, both in the structure itself and in the cladding and insulation materials. Due consideration must be given to this at an early stage of the design work. Fixings are subjected to two main forces: the first is Dead Loads, that is the actual weight of the supported stonework, which can be conservatively assessed using a density of 3000kg/m3. The second is Applied Loads, which are caused by wind pressure and suction, window cleaning equipment and any thermal or structural movements that may occur.
Fixings produced from stainless steel or non-ferrous metals are recommended and must be of sufficient size and strength to resist the relevant forces. Many factors including the structure, the stone, the size and thickness of the unit affect their final selection. These can fall into four main groups: Load Bearing, Restraint, Combined and Soffit fixings. For stone used as a masonry cladding, the principles for brickwork fixing can be adopted. Conventional wall ties should be used for restraint to the structure or inner leaf. If support is required shelf angles or other specialist fixings can be used.
However, for stone used as a thin cladding, there are a great variety of fixing methods and systems available. The specialist manufacturers such as Halfen should be consulted as well as BS 8298: 1994 before final selection is made.
USEFUL REFERENCES
British Standards
BS 8298: 1994 Code of Practice for design and installation of natural stone cladding and lining.
BS 5606: 1990 (1998) Guide to accuracy in buildings.
BS 6213: 2000 Guide to selection of construction sealants.
BS 5628-3: 2001 Code of Practice for Use of Masonry.
Source: Kirkstone.com