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Movement Joints in Natural Stonework |
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Interior Stone |
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SCOPE
This Data Sheet deals with the necessity for, and recommended spacings and widths of movement joints in Natural Stone masonry, exterior wall cladding, interior wall linings and tiling, and interior floor slabs and tiling.
INTRODUCTION
Like all building materials, natural stone exhibits dimensional changes in response to fluctuations in environmental conditions. Historically, stone was used in relatively large sections bedded on vveaker materials. Movements were slow and readily accommodated without distress, either by a build up of absorbable stresses or by minor changes in geometry.
The modern trend is to use stone in thin slabs, panels or tiles, frequently bedded on or attached by strong mechanical systems to other materials with different movement characteristics. As a result there is now a need to provide stress relieving movement joints to prevent damage resulting from restrained dimensional changes which can manifest itself as minor spalling ofjoints or major dislocation of the stone units.
It is difficult to calculate the anticipated movements with precision but, fortunately, in the majority of cases this is unnecessary. A calculation method for cladding is given in BS 8298. In other cases movement joints are provided at vvidths and spacings which are known from experience to be satisfactory and also vvhere movement joints occur in the substrate. The positions of movement joints must be established before work commences.
Movement joints must be properly sealed, according to the degree of exposure, with a flexible material which does not significantly impair movement. (See the companion Data Sheet "Sealing Joints in Natural Stone" issued by the Stone Federation).
The extension capability and recovery performance of the chosen sealant will frequently determine the actual joint width. However, this note suggests spacings and sizes for movement joints in various forms of common construction in normal environments, together with further reading. Movement joints should be provided at a distance equal to half the general spacing shown below from any corner, except where indicated othen/vise.
It is important that the designed minimum gap is not obstructed, for example by mechanical fixings, shims or mortar. A careful check should be carried out before joints are sealed.
Unusual circumstances, novel construction details or harsh or contaminated environments will all need speciah consideration and the extent of any movement should alvvays be carefully calculated.
NATURAL STONE MASONRY (EXTERNAL)
Vertically: 10mm wide @ 15m centres (5rn from any corner)
Horizontally: (in the outer leaf of cavity walls) 10mm wide @ every 3rd floor
Reference: BS 5390 "Code of Practice for Stone Masonry".
NATURAl. STONE CLADDING (EXTERNAL)
Vertically: 10mm wide @ 6m centres
Horizontally: 15mm wide @ every floor.
Reference: BS 8298 "Code of Practice for design and installation of natural stone cladding and lining".
NATURAL STONE LINING (INTERNAL)
Vertically: "lOmrn wide @ 6m centres (2m from re-entrant corners).
Horizontally: 6mm vvide at every floor or ceiling.
Reference: BS 8298 "Code of Practice for design and installation of natural stone cladding and lining".
NATURAL STONE WALLTILING (INTERNAL)
Vertically: 6mm @ 4m centres (2m from re-entrant corners).
Horizontally: 6mm at every floor or ceiling.
Reference: BS 5385: Part 1 "Code of Practice for the design and installation of internal ceramic, and natural stone, wall tiling and mosaics in normal conditions".
NATURAL STONE FLOORING (INTERNAL)
Perimeter: 10mm all round (except where width of floor is less than 2m).
Intermediate: 6mm @ 10m centres both ways on rigid substrate but matching joints in substrate. 6mm @ 6m centres both ways on flexible substrate or
with underfloor heating.
References: BS 5385: Part 5 "Code of Practice for the design and installation of terrazzo tile and slab natural stone and composition block floorings". Stone Federation Data Sheet "Laying an Internal Stone Floor to a Mature Concrete or Screed Base using a Semi-dry Bedding". Stone Federation Data Sheet "Laying Marble and Granite Tiles on to an existing Timber Floor".
NATURAL STONE PAVING (EXTERNAL)
None required, if laid on sand or semi-dry mix. Othen/vise 10mm @ 15m centres both ways and matching any joints in substrate.
NATURAL STONE SETTS (EXTERNAL)
None required.
Reference: Stone Federation Data Sheet "Stone Sett Pavings".
NATURAL STONE KERBS (EXTERNAL)
None required. |
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