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PATIO PAVING
NATURAL STONE
Slate For Paving |
Introduction
Slate has been used as a building stone for
centuries. Its laminar nature makes it easy to cleave and work,
rendering it a popular choice for roofing and walling as well as
paving. However, stone is heavy, and slate is no exception, so, hauling
paving or walling stone around the country didn't make much sense in
the days before motor vehicles and a nationwide transport system, and
consequently, it was only the high "added value" thin-cut slates for
roofing that were worth transporting any significant distance. So,
despite all it advantages, slate's use a paving material has been more
or less limited to its immediate area, notably the quarrying districts
of North-west Wales, the English Lake District, and the far South-west
peninsula. In Scotland and Ireland, where slate is scarce, whinstone
was, and is, a popular deputy. |
Welsh Slate
The quarries of Snowdonia are renowned for the
superb quality slate that is hewn from the shadows of Yr Wydffa, and
whole communities have worked the local slates of Blaenau, Llanberis
and Penrhyn for countless generations. The entire built environment is
dominated by this highly characteristic rock, with the heavier,
poorly-worked lump slate used for walling, and the beautifully cleaved
6-9mm (¼"-frac38;") thick slate used for roofing, while riven
flagstones would be used for pavements, or dressed to form kerbs and
edgings - even the headstones in the local graveyards would by formed
from lovingly-honed slate. |
Old Slate Flagstone Paving in Blaenau
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Slate Kerb in Dollgellau
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Slate Crazy Paving in Conway
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Welsh slate is known not only for its fine-grained texture but also for
its distinctive colouring, predominantly dark blues, blue-greys and the
unmistakable Penrhyn Purple, variously known as 'Plum' or 'Heather'.
This choice of colour can be combined with a range of formats, such as
sawn, riven or 'random' (as used for the labour-intensive "crazy paving") to offer clients and designers a thought-provoking selection.
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Blue-Grey Slate at Llanberis
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Purple Penrhyn Slate
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Dark Grey Blaenau Slate
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Slate waste
See also Decorative Aggregates
Decades of quarrying in North-west Wales have resulted in huge tips
of slate waste, (shards, scalpings, dust and unworkable stone) that has
been cast aside once the dressed slate has been prepared. One estimate
given to me is is that there are approximately 3 billion tonnes
(3,000,000,000) of slate waste littering the countryside in and around
the Snowdonia National Park alone. |
Slate waste used as a low-cost surface dressing alternative to gravel for a private driveway
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Slate waste used as both as a fill material and as a surface dressing to a public car park
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Although there is some use for this material as a low-cost fill, a
surface dressing or even as a cheap 'alternative' sub-base material,
supply still far exceeds local demand. The relatively recent
introduction of the progressive 'Primary Aggregates'
Tax has seen interest in this so-called waste material bloom and some
of the larger construction and civil engineering companies are actively
involved in transporting vast quantities of this 'waste' by rail into
central England for use as a selected fill material in road and rail
construction projects, but still, the huge 'tips' remain.
Simultaneously, the huge surge of interest in gardening and
landscaping over the past few years, has opened a new market for slate
waste as it has become the decorative surface dressing of choice with
many garden designers. Amazingly, what sells as a cheap fill for around
£5-10 per tonne in Bangor and Caernarfon, suddenly costs £6 per 25kg
bag by the time it's packaged and loaded onto the shelves of your local
Garden Centre of DIY Store. |
Decorative Slate Mulch in a Garden
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Other Uses
Slate
is highly versatile which allows it to be used in an almost limitless
number of ways. These are just a few ideas I've spotted on my travels
over recent years... |
| Cut into simple
rectangles with a 2:1 plan size, the resulting slate tiles can be laid
to a simple but effective basketweave pattern, as shown here. For a
more up-to-date interpretation, the tiles could be laid in a
herringbone pattern, possibly alternating contrasting colours on
consecutive courses, or using tiles with a different plan size ratio -
3:1 makes an intriguing herringbone layout.
See the Block Paving section for more information on laying herringbone patterns.
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Welsh Basketweave Slate
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Tumbled Slate Pavers
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For those looking for a more aged appearance, tumbled slate pavers are
also sold by some suppliers. These are 'perfect' pavers, prepared in
the usual way, but then put into a huge tumbling drum, similar to an
empty concrete mixer, wherein the pavers are turned over and over and
over, bashing against each other, and against the sides of the drum,
knocking off the edges and corners of the blocks, leaving them with a
'distressed' look that is said to age them.
Obviously, all this extra work increases the price per square metre, but the finished effect is rather charming.
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Of course, odd-shaped pieces of slate can be used as stepping stones in
gardens or informal areas. By laying a relatively flat surface
uppermost allows the mower to travel straight over the top without
damaging the blades. |
Slate Stepping Stones
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Slate and Granite
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Combining slate with other materials emphasises the qualities and
attractiveness of both. In this image, square slate blocks have been
used to form a break band in a section of granite paving. The dark,
neutral tones of the slate accentuate the warmer colours of the
feldspars and quartzes in the granite. |
Slate on Edge
This effect is actually quite wasteful, in that most of the slate lies
buried and unseen, but it is effective and is a good way of using old,
unwanted or broken roofing slates.
The slates are reduced to 'strips', anything from 30-100mm in
width, and then laid on a bed of mortar. The top exposed edges are then
tapped down to level, using a piece of timber to ensure they all end up
at the same level, and the joints are 'brushed-in' with a dry mortar
mix.
It's time-consuming and only really suitable for gardens and other decorative areas, but it makes a very distinctive border, edging or even a mowing strip.
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Slate on Edge Detail
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Slate on edge x-section
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Other Slates and alternatives
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| Although
Welsh slate has been featured on this page, there are slates from other
parts of the British Isles, notably the Green Slates of the Lake
District, sometimes known as Westmorland Slate, and the unmistakable
rusty-brown slates from Delabole in Cornwall, along with plain Greys
from elsewhere in the West Country and those from Donegal and Killaloe
in Ireland. All of these are eminently suitable as paving materials and
offer a more local feel to projects in those areas. |
Lakeland Green Slate ramp
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300x300mm Dartmoor Grey Slate Tiles
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Cornish Slate
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As noted on the page dealing with Indian Sandstone
paving, stone from all over the world is now finding its way to these
islands, and slate is no exception. Most of the slate being sold for
paving use is sourced from China and the quality varies enormously, so
a degree of caution is required when buying. Some of the slate products
sold as suitable for patio or pavement construction are actually
internal flooring grade tiles, totally unsuitable for the soggy
British/Irish climate and likely to delaminate with the first serious
frost. So make sure any imported slate is guaranteed to be suitable for
external use. |
Chinese Slate from Silverland Stone Ltd.
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Chinese Slate Floor Tiles
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Some of the slates being sold are highly decorative, such as the
Chinese Peacock Slate shown here, but bear in mind that the metallic
lustre of such a slate may disappear beneath the day-to-day crud that
accumulates on garden patios, and, to keep it looking at its best,
regular cleaning, or even sealing with a suitable sealant
may be required. Personally, I'd restrict use of such highly decorative
material to feature areas, rather than 'everyday' patios and pavements.
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Peacock Slate from Silverland
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Whinstone from Silverland
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Whinstone is a popular alternative in Scotland and North-eastern
England. It shares similar characteristics to slate and is becoming
easier to obtain further south. Most of the Whinstone paving taken down
to South-eastern England has a bluey-grey or almost turquoise
colouring, which is not to everyone's taste, but makes a bold statement
in a modern setting.
A note to contractors - it's worth noting that Whinstone is significantly harder to cut than is slate and the use of a power saw is highly recommended.
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Laying Slate Paving
By and large, slate paving is laid in the same way as any other stone paving, a process that is described more fully on the Laying Flags page.
However, because some slate pavings are relatively thin (any paving
less than 30mm thick is considered to be a 'tile' rather than a
flag/slab) many contractors find it easier to lay slate on a full
mortar bed. This ensures the slate is fully supported and the mortar,
once set, becomes the load-bearing layer, rather than relying on the
sometimes suspect inherent strength of the slate.
Overall, I would select an appropriate laying method depending on the thickness of the slate being laid...
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Type of Unit
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Thickness
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Method
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Tiles
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30mm or less
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Lay on 35-50mm of a very stiff Class IV mortar over a prepared base or sub-base
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Flags
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30-65mm
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Lay on 35-50mm of a 10:1 semi-dry bedding mix of grit sand and cement, as described on the Concretes page
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Blocks
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65mm or more
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Lay on 35-50mm of semi-dry bedding mix or, for flexible construction, use 35-50mm of clean grit sand
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Kerb and Edgings
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Varies
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Lay on 75-100mm of a C7.5 or equivalent concrete suitable for kerbing
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Table 1 - Selecting an appropriate laying method
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Some consideration should also be given to the jointing. Mortar pointed joints are suitable in most situations where rigid bedding
is used (ie, the slate is laid on mortar or a cement-bound bedding
mix). Close jointing should be avoided unless a distressed look is
desired, and, in such cases, a 2-5mm sand joint, as used with standard block paving, is a good choice, although polymeric sands can be used if preferred.
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