portlandstone technicalmanual

portland stone - naturally INTRODUCTION & STONE EXTERNAL CLADDING INTERNAL STONEWORK LANDSCAPE/EXTERNAL ANNEXES PORTLAND STONE QUARRIES MINES & FACTORY SELECTING STONE RECOMMENDED USES

History The Island’s stones are known to have been worked for nearly 1,000 years, Quarrying on Portland originally on local projects: Rufus Castle 11th century, Exeter Cathedral 14th ■ pre 1710 century and Portland Castle 1540s. From the early 1600s it started to become ■ 1710 to 1901 London’s dominant stone, with Inigo Jones using it on Banqueting Hall, the ■ 1901 to today stone having previously been used with success on elements of Westminster Abbey and the old gothic St Paul’s Cathedral.

Vast quantities of the stone went into London after the Great Fire of 1666 and up until this point the stone had come from the Landslips on the east coast of the Island. As demand continued into the eighteenth century, quarries opened up along the northern coast and during the nineteenth and twentieth centuries in the centre of the Island.

Despite these historically large volumes of stone leaving the Island for the construction of buildings in London and other major cities across Britain and the World, large reserves remain on the Island. From the map you can see that nearly 50% of the Island’s stone has been extracted. At the current rate of extraction there are many hundreds of years of stone to be won, albeit sometimes from more challenging locations.

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i. Quarries & mines Albion Stone is currently extracting dimension stone at two sites; Bowers and Jordans. We also have planning permission for a new mine at Stonehills, but this reserve will probably not come into production until 2010/11.

Bowers - The Quarry at Bowers has been operational since the late 1700s. It is leased from The Crown Estate but is now reaching the end of its life. In 1998 Albion Stone secured planning permission for a mining trial at the southern end of Bowers Quarry. Work began in 2002 and large reserves of Whitbed and Basebed remain in this location. Fantini machine in Bowers Mine High wall extraction at Bowers

Bowers is a deep quarry and, as a result of an 8 metre stand-off of untouched Jordans - Jordans is part of the Inmosthay Quarry in the centre of the Island, ground alongside the boundary and the gentle slope of up to 15 metres of which also includes Fancy Beach. The Quarry has been worked since the late overburden above the Portland Stone beds, a significant quantity of dimension 1800s. Albion Stone leases the southern section from The Crown Estate and stone was to be potentially wasted alongside the boundary. With the help of purchased the northern part of the site in 2006. The majority of the southern mining experts, Wardell Armstrong, a planning application was prepared and reserves lie under the grounds of the local cricket club. To avoid disturbing the passed by the Mineral Planning Authority to extract this stone using a series site at surface level, the company has applied and received permission to of small mines through a process known as ‘high wall mining’. Work began in extract the stone using mining rather than quarrying techniques. the Quarry in the Spring of 2006 and it is anticipated that up to 6,000 cubic metres of additional stone will be secured using environmentally sensitive The reserves to the north will be quarried using the diamond bladed cutting extraction methods. machines, hydra bags and the wire saws to shape the blocks. This process avoids the use of potentially damaging, dusty and noisy blasting as the primary extraction method, thereby protecting the surrounding environment, which has been designated as a ‘Site of Special Scientific Interest’ (SSSI).

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Independent & Admiralty - Both these quarries are owned by The Crown Estate and have been leased to Albion Stone since 1982. These quarries have been worked since the mid 1800s with the final dimension stones coming out of Independent in 2006, although some stocks of block still remain.

Stonehills - Albion Stone secured planning permission for a vast new reserve on the western side of the Island. The stone in this part of the Island has not previously been extracted due to the depth of the overburden. To quarry this site would involve a substantial rubble removal operation with all the associated dust, noise and visual impact nuisances. Jet Belt cutting through the face Wire saw of the stone Albion Stone will mine the stone from Stonehills site, thereby avoiding virtually all disturbance and nuisance to the surrounding residential properties. Mining also dramatically reduces the carbon footprint for the production of the stone.

Hydra bags inserted to move cut block Moving blocks from quarry face

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ii. Factory The Albion Stone Factory at Portland is one of the largest and most technically 2. Secondary Sawing advanced in the UK. It produces a wide range of Portland Stone products from The Secondary Sawing process produces the stones cut to the required slabs, cladding panels, pavers and tiles to the most intricate hand carved stones. dimensions from the slabs. The saws and blade are smaller than the primary saw and therefore more accurate, typically +–1.5mm. The Factory processes are: The wastage rate from this operation varies according to the size of the cut 1. Primary Sawing stone and the size of the slab. Typically between 20% and 30% of the stone is The Primary Sawing is the first cutting process to the block. The block is cut lost, but it will be higher for larger stones. into a series of slabs. The ashlar and tile lines are automated secondary saws designed to produce The Primary Saw is the largest saw in the factory. The Van Voorden has a large quantities of accurate stones. 3m blade, which is only is 13mm thick. This operation involves a significant amount of wastage from the actual physical cut itself. Typically up to 25% of the block is lost and this wastage, together with the expense of the specialist sawing and lifting equipment, explains the uplift in the cost from the block to the slab.

Van Voorden Block cut into slabs Secondary sawing

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3. Masonry The masonry (shaping of the stone) can be completed using either a planer, a saw or profiling saw, or a mason using hand tools.

Any masonry, because it is an additional process on the stone, will normally result in a significant additional cost.

4. Finishing All stones will go through the finishing process, which includes putting a rubbed finish (grit size 50) on all seen surfaces, a dimension check and palleting. Profiling the stones Masons shop

Mason with hand tools Pallet of finished stone

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Selecting stone

Roach - Portland Roach stone is a cavernous, Whitbed - The Portland Whitbed is a fine grained Basebed - Portland Basebed, also known as shelly, oolitic limestone which, because of the high limestone containing shell fragments distributed Bestbed, is the finest quality Portland Stone with shell content, has a colour closer to grey/creamy randomly and in bands throughout its mass. a close pore structure and little shell. The stone is white rather than the creamy white of the It is the traditional general building stone, being slightly less durable than Whitbed or Roach, and other Portland Limestones. It is a very hard and both extremely durable and able to be used for therefore may not be appropriate if a long life extremely durable material and is therefore ideally intricate masonry. is required as a general paving stone, or in areas suited to exposed sites. The pronounced shell of very high exposure. Although originally used structure has also encouraged its use as decorative primarily as a monumental stone and carving flooring or cladding panels. stone, it has more recently been specified on high quality, prestigious office developments and used extensively for flooring.

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Recommended uses

Portland Portland Portland (A) All porous Limestones draw in moisture from surrounding media. Roach Whitbed Basebed Therefore, contact with soils without protection could cause slight staining, Load Bearing Construction particularly during the first two years and if the soils are heavily contaminated Masonry ••• with mineral salts. Portland Stone should never be used as a formwork for in Bridges at waterline ••x situ concrete as alkali salts from the concrete may lead to discolouration. Retaining walls • A • A • A Non Load Bearing (B) Due to the open nature of this stone, the designer needs to be certain Cladding ••• that this stone is suitable in the proposed location. Columns ••• Lintels ••• (C) Roach is a hard stone and is, therefore, not easily carved or worked by a Plinths • A • A • D mason. More time and therefore more cost should be allowed for working this Copings ••• stone in comparison to other Portland Limestones. Thresholds, steps & stairs • B ••D External paving • B • x (D) Portland Basebeds, although physically stronger, are less durable than the Internal flooring • B •• other Portland Stones. The higher Saturation Coefficient and Salt Crystallisation Fireplaces • C •• results indicate that if these stones are continually saturated and frozen, then Carving & moulding (incl headstones) • C •• damage to the surface could occur. Although this damage would probably Sculpture • C •• only occur in the first 1 to 2mm of the stone, the resulting pitting effect is likely to be unsightly. We therefore recommend that further advice is sought NOTE: It is recommended that in most locations, Portland Stone should be before using Basebed in these exposed areas, ie external treads not protected used on its natural bed. Although the stone is slightly stronger when used on by a dpc etc. its natural bed, this advice is given for aesthetical reasons. The only exception to this rule is paving, where we recommend using the stone edge bedded. (X) Not recommended Again, this is for aesthetical reasons as the larger oyster shells can appear as rather unsightly large round shells when cut horizontally.

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Albion Stone plc Factory ©Albion Stone plc Robert Denholm House, Bletchingley Road, Easton Street, Portland, Dorset DT5 1BW Portland Stone Technical Manual, March 2008 Nutfield, Surrey RH1 4HW England Tel: 01305 860369 Fax: 01305 860379 All rights reserved Tel: 01737 771772 Fax: 01737 771776 email: [email protected] email: [email protected] www.albionstone.com Jordans Quarry Easton Street, Portland, Dorset

Bowers Quarry Easton Street, Portland, Dorset

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Contents

INTRODUCTION & STONE EXTERNAL CLADDING

Introduction 7 Feasibility/planning 17 vi. Stone thickness 27 The Company 8 British/European Standards 17 vii. Cavities 27 Portland Stone 9 i. Introduction 17 Cavity fire stops 27 Geology 9 ii. Selecting the stone 18 Insulation 27 History 10 Inspection of the buildings 18 Weep holes 27 The Quarries, Mines & Factory 11 Inspection of the quarry/mine 18 Cavity trays 27 i. Quarries & Mines 11 Inspection of the quarry range panels 19 viii. Fixing contractor 28 Bowers 11 iii. Technical data sheets 21 ix. Programme 28 Jordans 11 Stone testing 21 Stone on Precast 29 Independent & Admiralty 12 Sampling Plan 21 i. Fixings 29 Stonehills 12 Impact damage 21 ii. Movement 30 ii. Factory 13 Traditional hand fixed 22 Sealants 30 Primary Sawing 13 i. Introduction 22 Joint width 30 Secondary Sawing 13 ii. Fixings 23 Cement lime mortars 30 Masonry 14 iii. Movement joints 24 iii. Stone detailing 31 Finishing 14 Compression joints 24 Unit sizes 31 Selecting stone 15 Expansion joints 24 Stone detailing 31 Roach 15 Sealants 24 iv. Stone on Precast contractor 32 Whitbed 15 iv. Mortars 25 v. Programme 32 Basebed 15 Joint width 25 Recommended uses 16 Cement lime mortars 25 v. Stone detailing 26 Unit sizes 26 Stone detailing 26 Weathering 26

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Contents continued

EXTERNAL CLADDING continued INTERNAL STONEWORK

Rainscreen cladding 33 ii. Regular maintenance 41 British/European Standards 43 i. Ventilated rainscreen cladding 33 Joints 41 Introduction 43 ii. Fixings 34 Movement joints 41 Selecting the stone 44 iii. Movement 35 Water erosion 41 i. Samples 44 Joints 35 Organic 41 ii. Inspection of past projects 44 Cavities 35 Surface staining 41 iii. Inspection of the quarry/mine 44 Cavity fire stops 35 Physical damage 41 iv. Technical data sheets 45 Insulation 35 iii. Cleaning 42 v. Inspection of the quarry range panels 45 iv. Stone detailing 36 Frequency of cleaning 42 Flooring 46 Unit sizes 36 Cleaning method 42 i. Introduction 46 Stone detailing 36 Graffiti 42 ii. Flooring substrate 47 v. Stone thickness 36 Plant growth 42 Levelling screeds 47 vi. Weathering 37 Nameplates and other fitments 42 Under-floor heating 48 vii. Fixing contractor 37 Movement joints 48 viii. Programme 38 iii. Stone sizes 49 Cladding maintenance 39 Laying the stone 49 i. Construction maintenance 39 Joints 50 Delivery/packaging 39 Grouting 50 Storage/handling 39 iv. Tiling on different structures 51 Site 39 Stone flooring on an existing timber structure 51 Cleaning 40 Stone flooring onto pedestals 51 Painting 40 v. Treads & risers 52 Staining 40 vi. Wet areas 52

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Contents continued

INTERNAL STONEWORK continued LANDSCAPE/EXTERNAL

vii. Construction maintenance 52 iv. Lightweight tiles 57 British/European Standards 61 Delivery/packaging 52 v. Construction maintenance 57 Introduction 61 Storage/handling 52 Delivery/packaging 57 Selecting stone 62 viii. Sealants and impregnators 53 Storage/handling 57 i. Samples 62 ix. Regular maintenance 54 vi. Maintenance 57 ii. Inspection of past projects 62 Cleaning and stain removal 54 Decorative internal stonework 58 iii. Inspection of the quarry/mine 62 Internal wall linings 55 i. Structure 58 iv. Technical data sheets 63 i. Introduction 55 ii. Design 59 Walling 64 ii. Internal stone cladding 56 iii. Installation 59 i. Introduction 64 Structure 56 iv. Construction maintenance 60 ii. Types of walling 64 Fixings 56 Storage & handling 60 Ashlar walling 64 Stone thickness 56 v. Regular maintenance 60 Split faced walling 64 Joints 56 Hand dressed walling 64 iii. Wall tiles 56 iii. Construction 65 Structure 56 iv. Site practice 65 Movement joints 56 v. Maintenance 66 Fixing 56 Cleaning 66 Joints 56 Paving 67 i. Introduction 67 ii. Paving substrate 67 Base 67 Bedding 67

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Contents continued

LANDSCAPE/EXTERNAL continued ANNEXES

iii. Installation 68 1. Determining panel dimensions using iv. Technical properties 68 BS 8298 Part 2: 2008 72 v. Site Practice 68 2. Energy conservation 76 vi. Maintenance 69 3. Sampling plan 79 vii. De-icing sales and chemicals 69 4. Technical data sheets and CE certificates 81 Ornate 70 5. Health and safety/site handling 82 i. Introduction 70 6. British and European Standards 84 ii. Stone selection 70 7. Contacts list/reference section 88 iii. Headstone fixing 71 Other natural stone publications 91 iv. Sculpture installation 71 v. Maintenance 71

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Introduction This 3rd edition of the Albion Stone Technical Manual has been updated to include the latest practices and standards to assist in the correct and skilful use of Portland Stone in its numerous applications.

To aid the selection process, full technical information on each of the beds of Portland Stone supplied by Albion Stone is supported by BRE test data and the aesthetic and physical properties of the stones are detailed.

The practical aspects of masonry installation are outlined to ensure that the choice of stone fulfils its maximum potential and gives several lifetimes of elegant usage.

The information within this manual is accurate at the time of publication, but due to frequent updates in British and European Standards, Building Regulations and Codes of Practice, it should be regarded in conjunction with those currently in force, and is not legally binding on the company. It should be used as a source of information only and does not seek to advise on professional techniques; it is recommended throughout that specialist advice Mining at Portland is sought where required and competent, experienced stone fixers are used for all applications.

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The Company Albion Stone plc is a privately owned company, whose association with the quarrying and specialist masonry production of the finest quality Portland Stone spans nearly three-quarters of a century.

As well as its own recently purchased quarry at Jordans, the company has leases covering all The Crown Estate Portland quarries with vast reserves, giving security to expand and continually invest in new capital equipment.

Our Portland factory is one of the largest and most productive masonry works in the UK. Continual and controlled expansion enables us to produce a full range of Portland Stone products from blocks and slabs to the most intricate masonry works.

Albion Stone’s commitment to excellence in all aspects of quarrying and masonry production includes a continuous, phased system of excavation, stone removal and ground restoration, empathetic with the environment. Albion Stone produces an increasing percentage of stone from mines in order to lessen the impact on the environment. Factory

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Geology Portland Stone originated in the Jurassic period over 145 million years ago, when dissolved carbon dioxide in the shallow tropical seas reacted with Top/Sub Soil the calcium and bicarbonate ions to form thick layers of calcium carbonate Rubble and Clay Beds (calcite). Scattered among these grains (ooliths) were fragments of shells from 3-4m oysters, scallops and clams that lived on these shifting lime sands. Portland Blue 0.5-1m Bottom Rubble 1-2m A sudden drop in sea level caused a rapid, deep burial of these Portlandian Cap 3-4m

beds by deposits from saline lagoons, resulting in the pore spaces between Lower Purbeckian Beds the individual ooliths never becoming completely occluded by natural calcite Portland Roach 2-3m cement. This geological event gives Portland its unusual properties of immense Portland Whitbed 2-3m strength under compression, excellent weathering characteristics, coupled Curf 1m with extreme ease of cutting and working. Portland Basebed 2-3m Portlandian Freestone Series

Cross section through Isle of Portland Tout Quarry (worked out) Bowers MineFuture mining Weston operations at Bowers Quarry Stonehills

Fortuneswell Po rtlan Low d Sto er P ne Beds urbeck Beds Portlan Portland d San Portland Harbour ds Bill Uppe r Kimmeridge Cl Sea level ay Sea level

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