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Irish Blue Limestone is a highly versatile
material that can be used in many different forms.
The
most basic is the unprocessed limestone block as extracted from the quarry. This is common
to all producers and may be purchased from some companies.
The majority of the companies use the blocks as a source of
raw material for inhouse processing. The finished products may be broadly divided into
ashlar and slab.
Ashlar, where the material is a structural component of the
construction, is the traditional method of utilizing the limestone. This encompasses a
wide range of products including blocks, sills, lintels, quoins, cappings, steps, door and
window surrounds, kerbs, paviors and setts. A very wide range of finishes can be applied
to ashlar from the simple natural split face to complex chiseled patterns. A number of the
producers have the capacity to manufacture fully hand-dressed ashlar and for certain
restoration work this may be an important feature to assure continuity with the existing
structure.
Modern ashlar is produced to close dimensional tolerances
by the utilization of diamond sawing techniques. The finishes available for the limestone
slab can be applied to ashlar. Where mechanical finishes are specified for the exposed
face, the thickness will be fairly consistent. Split or hand-dressed finishes will have
more variation in thickness. Ashlar is normally placed on the bed.
Limestone slab enables natural stone finishes to be applied
as a cladding to any structure without the additional weight penalty associated with
ashlar. A wide range of mechanical and manual finishes can be applied to the exposed face
although this may impose some limitations on the minimum thickness. The limestone slab is
available from the producers in untrimmed or cut to size form. There are close and
consistent tolerances in the thickness and flatness of the slabs. The blocks are normally
cut parallel to the bed to produce slabs but much thicker contra-pass slabs are also
available from many of the producers.
Limestone Block
The limestone strata that are worked to yield Irish Blue Limestone are fairly massive and
pose few limitations on the length or breadth of the blocks that can be extracted.
The thickness of the blocks is generally governed by the
presence of major stylolites and may vary from 0.5 to 3.0 metres.
The companies, which supply unprocessed limestone,
generally aim to extract blocks about 2.5 metres long 1.3 metres wide and 1.0 metres thick
although the nature of the material can result in some dimensional variation. The
resulting block, which would weigh about 8.5 tonnes, is easily handled by the normal
quarry equipment and will give a good match to the 32 tonne Statutory Limit for road
transport in Ireland.
Larger blocks may be available but as this would be to
order the exact requirements would need to be discussed with the individual quarries.
Limestone Slab
The cutting equipment generally available in the Irish Quarries is geared to the
production of limestone slab with face areas of about 2.5 by 1.3 metres. The maximum
routine cutting capacity of most of the plants is about 2.8 by 1.5 metres but most have
the capacity to handle considerably larger sizes to special order. The dimensions given
relate to the maximum regular rectangular block that can be cut from the slab rather than
the average length and width of the untrimmed slab. The sizes are to some extent a
historical legacy but have also proved ideally suitable for the containerized transport
that is an essential component in serving the rapidly growing overseas market for Irish
Blue Limestone.
A wide range of cut slab thicknesses are available but the
production is generally geared round 20, 30, 40 and 50 millimetres thickness when the
slabs are destined for honed or polished finishes and 40, 50, 60, 80, 100, 120, 150, 180,
200, 220, 240, 250, 280, and 300 millimetres for general construction stone. The thinner
slabs are normally available ex-stock from the producers and the remaining sizes can be
rapidly scheduled within the normal plant production cycle. Intermediate thicknesses can
be produced to order but the requirements should be discussed with the individual
quarries.
A number of standardized designs for ashlar components used
in the construction industry are outlined in the latter part of this manual. Some items
are available ex-stock from the quarries but most are manufactured to order with fairly
short delivery times. All sizes given are in millimetres.
Continental practice, when limestone is being used for
internal applications, has tended to standardize on 20 or 30 millimetre panel thicknesses
and the Irish Blue Limestone producers all have capacity to achieve a rapid turn round in
orders for these sizes.
The producers are also geared to supply cladding or ashlar
specifically designed for an individual project. Full technical support including design
and detailing of the stone work is available from the Limestone Producers.
Where the ashlar and finished cladding panels are specific
to a building, there is a tendency to specify the maximum size of stone that can be used
in any particular area of the building facade. The thickness of the stone must also
reflect the surface finish chosen. Caution should be shown in the sizing of the individual
components if severe problems are to be avoided at the fixing stage. As a general rule,
the maximum dimension length should be less than 1.5 metres. Economies of production and
fixing, favour the surface area of the stone not being less than 0.5 square metres in area
for cladding. Local building regulations may impose additional constraints on the
dimensions particularly for thinner cladding panels. A wide range of mounting systems are
produced for cladding panels. The type chosen will depend on the location and size of the
cladding. Building regulations and country 'Standards' will give specific requirements for
cladding fixings and must be checked for details. |
