Shropshire Building Stone: Grinshill Sandstone, Wenlock Limestone and the Red Stones

Why does Shropshire have so many building stones?

Walk from Shrewsbury to Ludlow and you will pass cream, red, grey and almost black walls, sometimes in the same village. The reason is geology. Rocks from a long run of geological periods, from the Precambrian to the Triassic, come to the surface in Shropshire,^[8] and before railways and cheap brick, most builders used what lay within a few miles. The result is a county where the stone of a wall often tells you the ground the village stands on. Local geology even gave the world several of its geological names: the Shropshire Hills AONB notes that Murchison and Lapworth named formations such as Caradoc, Wenlock and Ludlow after local places.^[5]

The most useful single source is the Strategic Stone Study: A Building Stone Atlas of Shropshire (the Atlas, below), compiled by Andrew Jenkinson for the Shropshire Geological Society and sponsored by English Heritage, which lists the main stones with their geology, quarries and buildings.^[1] The Atlas belongs to Historic England’s Strategic Stone Study, a county-by-county survey of historic building stones; its authors stress that it does not replace expert advice, and that replacement stone should match the original’s mineral composition and physical properties, especially porosity and permeability.^[7] Much of what follows is drawn from it, with a few details from other cited sources. Stone names in the Atlas are often local ones, so you will meet terms such as Buxton Rock, Hoar Edge Grit and Keele Beds that you will rarely meet outside the county.

Stone by age: a quick geological ladder

Geologists name rocks by the period in which they formed. In Shropshire the older stones tend to come from the hills in the south and west, and the younger, softer red and cream sandstones from the plain to the north and east. The diagram shows the main stones by period, with approximate ages. Treat it as a way of organising the names, not as a complete list.

• Precambrian and Cambrian: the oldest rocks, in the Long Mynd and around Church Stretton and the Wrekin.
• Ordovician: hard quartzites and flags in the Stiperstones and Shelve areas.
• Silurian: the limestones and siltstones of Wenlock Edge, Corvedale and Ludlow.
• Carboniferous and Permian: red sandstones in the Severn valley and around Shrewsbury, Bridgnorth and Alveley.
• Triassic: the Grinshill sandstones and red stones of the north Shropshire plain.

Grinshill Stone: the stone of Shrewsbury

Grinshill Stone is the best known Shropshire building stone. The Atlas describes it as a white, fine to medium-grained, quartz-cemented sandstone of the Helsby Sandstone Formation (Triassic), virtually free of iron, quarried at Grinshill and Clive, north of Shrewsbury.^[1] Wikipedia, by contrast, describes the Grinshill sandstone as Permo-Triassic New Red Sandstone of the Helsby Sandstone Formation, so you may see the age given as Permo-Triassic rather than Triassic.^[8] Its freedom from iron is why it stays pale rather than rusting to brown or red, and why it carves cleanly: it was favoured for door and window mouldings and for ashlar, which means dressed blocks laid in neat courses.

Grinshill Stone was preferred for high-status buildings from medieval times, and the BRE records quarrying in the area since Roman times.^[2] The Atlas lists Haughmond Abbey (medieval), the late 16th-century Old Market Hall and library of Shrewsbury School, Attingham Hall, the Lord Hill monument and Shrewsbury railway station (1848).^[1] Its heyday was from the mid-19th to early 20th century, and it supplied dressings for most Victorian church restorations in the county. The west door of St Laurence's Church in Church Stretton (c.1870) is in Grinshill Stone.^[1]

The current Grinshill quarry, described by the Building Research Establishment as lying between Clive and Preston Brocklehurst, has about 6 metres of hard white flagstone below roughly 1 metre of overburden, and then about 27 metres of building stone, usually in beds of around 1 metre, though a bed can reach 3 metres.^[2] That is a very large, even resource, which helps explain why the same stone appears across so many buildings over so many centuries.

Red stones of Shrewsbury and the Severn valley

Shrewsbury's older buildings are often red. The Atlas lists the Keele Beds, a Carboniferous red to purple sandstone, quarried at the Quarry (Belvidere) and Preston Boats in Shrewsbury and at Redhill, in medieval Shrewsbury, including Shrewsbury Abbey, St Mary's, St Giles and St Julian's, and the 19th-century chapel at Shrewsbury School. Further out it was used at Acton Burnell Hall and church (13th century) and in Victorian cottages in the village.^[1]

Red sandstones also run south down the Severn. The Atlas describes Bridgnorth Sandstone as a strong red, wind-blown (aeolian) sandstone, often marked by bee borings, used in Gothick-style buildings and the gate lodge at Dudmaston.^[1] Alveley Sandstone is bright red and was used for the core of Alveley village from the 17th century.^[1] Highley Sandstone, greenish grey, was used in Bridgnorth Bridge, rebuilt by Telford in 1796, according to the Atlas. Nesscliffe Stone, a less resistant red stone, was used by Telford to restore Shrewsbury Castle in the 1790s.^[1]

The Atlas notes that some red stones, such as Nesscliffe Stone, are less resistant to weathering, so check for flaking and rounded corners on old red walls before you repair or clean them.

Limestone and siltstone: Wenlock Edge, Corvedale and Ludlow

South of Shrewsbury the stone turns grey. Wenlock Limestone is a pale grey, rough, fossiliferous limestone of Silurian age, quarried along Wenlock Edge. The Atlas lists it in the tower and south nave wall of Holy Trinity Church in Much Wenlock, in other Much Wenlock buildings, in Wilderhope Manor and at Easthope.^[1] The British Geological Survey defines the Much Wenlock Limestone Formation as pale grey nodular to thinly bedded limestones with reef bodies, of Silurian (Homerian) age, with type sections near Much Wenlock; the Atlas adds that the stone is rarely used for anything other than coursed rubble and usually needs brick or sandstone for quoins, sills and dressings.^[3][1]

Around Ludlow and in Corvedale the stones are siltstones, fine-grained rocks formed from silt. The Atlas lists Whitcliffe Stone, a grey to light brown laminated siltstone quarried on the Teme opposite Ludlow, in older Ludlow buildings and Dinham chapel; the Ludlow siltstones used in Clun, where about 85% of the houses built before 1900 are stone-built; and the paler brown Corvedale siltstones in villages such as Diddlebury, Munslow, Shipton, Brockton and Bourton.^[1] Siltstone breaks into flat or blocky pieces and is usually laid as rubble, rough stone in irregular courses.

The Atlas also records Aymestry Limestone, an impure limestone, as used in garden walls at Corfton, and suggests the View Edge quarries above Stokesay were probably used mainly for lime-burning.^[1] Limestone was also burnt for lime, the basis of traditional mortar and plaster.

Hill stones: the south-west and the Long Mynd

The hills have their own tough stones. Buxton Rock, a greenish-grey Longmyndian tuff, was quarried at All Stretton and used there and in cottages in Church Street, Church Stretton; it breaks into rough tetrahedra with black-stained joints.^[1] Purple Longmyndian conglomerate and random rubble appears in St Laurence's Church, including the Norman nave and north door. Stiperstones Quartzite is pure white and very hard, used for The Bog School (c.1870), some mine buildings and scattered cottages. Mytton Flags, a dark grey laminated stone that weathers to ferruginous brown, was used in settlements on the western flank of the Stiperstones.^[1]

On the Clee Hills, Dhustone, a dark blue-black dolerite, was quarried on Brown Clee and Titterstone Clee and used in Ditton Priors and Cleobury North.^[1] Near the Welsh border, the Atlas records Alberbury Breccia (Cardeston Stone), a salmon-pink stone made of Carboniferous Limestone fragments in a red sandstone matrix, used in the medieval castle at Alberbury, the 13th-century tower of St Michael's and most local vernacular buildings until about 1900.^[1]

Roofing stone: Harnage slates

Not all stone went into walls. Harnage Stone Slates are a fissile (easily split) roofing stone from Lodge Hill and Bull Wood above Acton Burnell. The Atlas lists their use at Stokesay Castle, the Abbot's House at Wenlock and in medieval Shrewsbury, and most recently in repair of the church roof at Pitchford.^[1] Stone slates are far heavier than clay tiles, so a roof covered in them needs a strong frame.

The Ironbridge Gorge has its own story: the Atlas lists Big Flint Rock, a Coal Measures sandstone, in Buildwas Abbey, possibly Wenlock Priory, and the Bedlam Furnaces.^[1]

Dated uses in Shropshire stone

The Atlas gives a small number of dates that anchor the stories above. Together they show how stone use changed: medieval churches and abbeys used the red and cream sandstones; the late 18th century saw engineers such as Thomas Telford working in local stone at Shrewsbury Castle and Bridgnorth Bridge; and the railway age made Grinshill Stone a standard for civic and station buildings.

How to work out which stone you are looking at

You cannot reliably identify a stone from a photograph, and colour is only a guide because weathering, lichen and soot change it. Use the sequence below as a way of narrowing down, then confirm against a published source such as the Atlas or a local geologist.

• Look at where you are. Local stone is the best clue, and the map and the table of stones will tell you which are likely nearby.
• Look at a clean, fresh face if you can: a broken corner, a gatepost or the inside of a ruined wall.
• Note the grain. Sandstones feel gritty, siltstones are fine and slippery to the eye, limestones may show fossils such as shells and corals.
• Note how the stone breaks: thin flags, rough blocks or smooth blocks.
• Look for the surface symptoms of decay: flaking, honeycombing, powdering or green algae.

Myths about Shropshire stone

• “All old Shropshire buildings are timber.” Not so. Most abbeys, castles, churches and many houses are stone, and many timber buildings sit on stone footings.
• “Red sandstone is the same everywhere.” The Atlas separates red stones from several geological periods, and their durability differs.
• “Grinshill Stone is only used in Shrewsbury.” It was widely used across the county and beyond.
• “Stone never needs maintenance.” It does: mortar, drainage and cleaning methods matter, and the wrong repair can cause decay.

Caring for a stone house, inside and out

Old stone walls are built to breathe. They absorb water in wet weather and let it dry out again, provided the mortar and any plaster are softer and more permeable than the stone. Hard cement mortar and pointing do the opposite, forcing water to leave through the stone and speeding decay. Use lime mortar for repointing, and take specialist advice before cleaning. Historic England says unsuitable repointing is among the most frequent causes of damage to historic buildings, and that sound historic mortar should be left undisturbed.^[4] Sandblasting and strong acids can destroy the hard outer skin of a stone. Ashurst explains that an abrasive stream cannot on its own tell soiling from the stone beneath, so damage depends on the operator’s skill, and she recommends on-site trials before any contract. (The point about the hard outer skin and about acids is general background, uncited.)^[6]

Inside, a lime plaster finish suits a stone house and so do plaster details. A plaster ceiling rose or a plaster wall light on a lime-plastered wall belongs to the same family of materials, and a pale surround can lift a dark rubble-stone room. Our guides to lime and gypsum plaster and restoring a period home in Shropshire explain the differences. Follow each product's own instructions (see our paintable plaster guide for finishing), use a qualified electrician for wiring, and check with your conservation officer before fixing anything to a listed building.

Keep reading

• Shropshire architectural heritage
• Brother Cadfael's Shrewsbury: the abbey and medieval town
• Period towns in the Welsh Marches
• Lime v gypsum plaster
• Black-and-white Shropshire: how to read a timber frame
• Stokesay Castle and the fortified manor houses of the Welsh Marches
• Georgian Shrewsbury: streets, townhouses and details
• Thomas Telford in Shropshire
• St Chad’s and St Mary’s: the churches of Shrewsbury
• Shrewsbury Flaxmill Maltings: the first iron-framed building
• Thomas Farnolls Pritchard: the architect behind the Iron Bridge
• Victorian Shrewsbury: the railway station and landmarks

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Frequently asked questions

What is the main building stone of Shropshire?

There is no single one. Grinshill Stone, a cream sandstone from north of Shrewsbury, is the best known, but red Keele Beds sandstone, Wenlock limestone, Ludlow siltstone and hill stones such as Buxton Rock are all widely used.

What is Grinshill Stone?

A white to cream, fine to medium-grained, quartz-cemented Triassic sandstone of the Helsby Sandstone Formation, quarried at Grinshill and Clive near Shrewsbury. It is nearly free of iron, so it stays pale and carves cleanly.

What stone is Shrewsbury Abbey built from?

The Building Stone Atlas of Shropshire lists Shrewsbury Abbey among buildings using Keele Beds red sandstone and Shelvock Quarry stone.

What is Wenlock limestone?

A pale grey, rough, fossiliferous limestone of Silurian age quarried along Wenlock Edge. It was used in Holy Trinity Church, Much Wenlock, and in Wilderhope Manor.

Why are some Shropshire buildings red and others cream?

Different stones came from different geological formations. Red stones such as the Keele Beds and Bridgnorth Sandstone contain iron minerals, while Grinshill Stone is virtually iron-free.

Where can I find out which stone a Shropshire building is made of?

The Building Stone Atlas of Shropshire, compiled for the Shropshire Geological Society and sponsored by English Heritage, lists the main stones by geology, quarry and building. National Heritage List entries often name the material.

Can I clean or repoint an old stone wall myself?

Use lime mortar rather than cement for repointing and get specialist advice before cleaning. Harsh cleaning can damage the stone surface, and listed buildings need consent for many works.