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TRANSCRIPT
RE
GISTERED
FIR
M
Cladding by BURLINGTON
CI/SfB
March 2002
(41) Se5
This brochure describes the use of Burlington stone as externalwall cladding and internal wall lining to achieve a natural finishwhich will last the lifetime of a building.
Stone by Burlington was formed by the progressive deposition offine silt during the Silurian age. The deposits weremetamorphosed by intense heat and pressure within the earth’scrust, creating a totally waterproof non-porous material with a finecompact texture and great strength.
For over three hundred years Burlington has quarried this naturalmetamorphic stone from the heart of the English Lake District.Architects and designers around the world have long takenadvantage of its natural beauty, durability and adaptability tocreate classic weather-resistant details and surface finishes.
Benefits of natural stone
The richness and character of natural stone impartweatherproofing, durability and prestige to any building. With itsgreat strength and natural beauty, Burlington natural stone offersunique advantages, it is:-
• of excellent appearance;
• hard, dense and very durable;
• impervious to water;
• resistant to frost, acid rain, salt attack and pollution, cycles of wetting and drying, and extremes of temperature;
• colour-fast – will not fade on exposure to UV light;
• chemically inert – compatible with all other building materials;
• resistant to (and will not support the growth of) mosses, lichens, algae or fungi;
• non-combustible;
• self-cleansing – very little maintenance required.
When correctly detailed and installed, Burlington stone claddingand linings have a service life in excess of one hundred years. The performance characteristics of the material have beendetermined by extensive testing and are given on separateProduct Data sheets available from Burlington.
Cover photo: Aronoff Center for the Arts
STONE BY BURLINGTON
2 Cladding by BURLINGTON
Burlington’s quarries produce five distinctivetypes of stone, all of which are suitable forcladding and lining applications:
• Elterwater: a pale green stone;
• Bursting Stone: an olive green stone;
• Broughton Moor: a mid green stone;
• Brandy Crag: a silver grey stone;
• Blue Grey: a blue grey stone.
With the exception ofBlue Grey, which is an eventone throughout, each stone ishighlighted by contrasting veinswhich emphasise its naturalorigins and add character toany facing application. When combined in a singlescheme the different typesblend harmoniously, providingcomplement and contrast.
The variety of surface treatments which can beapplied to each stone increases the range ofoptions for any design scheme; those finishesinclude:
waterjet: the surface of the stone is worked withhigh-pressure water jets to give a non-slipmatt finish;
honed: a smooth finish with a slight sheen,produced by using a polishing head;
sanded: sawn stone slabs are coarsely polished;this removes saw marks and leaves a semi-smooth, regular finish;
cleft: with this traditional treatment the stone isriven along its line of cleavage to reveal thenatural grain; this gives an undulatingsurface with great character;
gritblasted: a high-pressure airline projectscoarse-grained grit onto the top surface ofthe stone producing a finish similar to cleft,but available on slabs of greater size.
flamed: the top surface of the slab is burned offusing a high temperature torch, giving anirregular textured finish;
textured: the top surfaces of sawn slabs arepneumatically tooled to produce a pitted orgrooved surface.
Burlington are continually developing the range oftreatments available. Sample cards showingmaterials and finishes can be supplied: pleasecheck the availability of a finish on a particularstone before specifying. If you require aspecialised effect we will be happy to discusswith you how it can be achieved.
Burlington stone for cladding and lining isavailable in 20mm, 30mm and 40mmthicknesses, as described in Table 4 ofBS 8298 1994: “Design and installation of naturalstone cladding and lining” (MIA DesignManual IV*: 1", 1.25" and 1.5"). To meetindividual project requirements, stone can be cutand shaped to other thicknesses and profiles ifrequired.
STONE BY BURLINGTON
Cladding by BURLINGTON 3
* Whilst the principles for specifying and installing natural stonecladding are universal, codes and standards vary betweencountries. Where variations exist the specific requirements forthe USA are given in brackets.
ÒStone is of the earth but, when it is worked, it receives the sky and becomes architecture.Ó
(Christian Norberg-Schulz)
The use of thin stone panels to *clad and *linebuildings has a long history extending from theRoman period. Over the centuries architects haveemployed stone in this fashion to achievebuildings of grace and grandeur: stone hasechoed the form of the building, emphasisedstructural elements such as columns and arches,and decorated interiors and exteriors.
*cladding refers to an external veneercovering a structure: it may include bothvertical and horizontal surfaces andcarries no load other than its own weight;
*lining refers to an internal wall coveringwhich carries no load other than its ownweight.
Advances in building technology over the lastcentury have removed many of the structuralconstraints upon the use of building materials,giving designers greater freedom in the treatmentof surfaces. Although cladding and lining areoften regarded as two dimensional, stoneremains a material with three dimensions, andthis most basic of properties can be used to goodeffect.
Historically, the functional format of stone incompression revealed itself in the finishedconstruction. In much the same way, theprinciples of masonry construction can be usedas a starting point for developing attractive facingschemes. By referring to the functionalrequirements of masonry in the shaping of thestones, the coherence of the surface treatmentcan be increased and a sense of massdeveloped.
Facing set in bonded coursing recalls the originalfunction of stone, allowing structural elements tobe defined by the treatment of the facing. Othermaterials may be introduced to counterpoint thestone and the design can be further enhanced by
variations in the finish of the panels.Plain butt joints will emphasise thecontinuity of the stone, whilst rebatedor chamfered edges will give greaterarticulation to the facing.
REALIZING THE POTENTIAL OF CLADDING
4 Cladding by BURLINGTON
Project: Miller Performing Arts Center, Alfred University
Architect: Kallmann, McKinnell & Wood
Splashback in honed Brandy Crag
Project: Central Library, Los Angeles
Architect: Hardy Holzman Pfeiffer Associates
Cladding to escalator in honed Elterwater
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The use of quoins at corners, the development ofcolumns or pilasters and the use of voussoir-likestones at openings are all references totraditional forms of loadbearing construction.
The formal and functional attributes of doors andwindows can be accentuated with jambs andreveals, allowing components to be set back fromthe wall line, thus producing shadowing andarticulating the elements. Introducing cills andstring courses adds interest to openings and hasthe functional benefit of throwing rainwater awayfrom the wall surface.
By contrast, stone cladding using moderntechnology may be used as a wrap-around skinwhich makes little reference to the underlyingstructure.
In rain screen cladding the joints betweencladding units are left open and the cavity behindthe cladding is ventilated to drain away andevaporate any moisture which penetrates thejoints. Joints can be narrow and regular, they donot have to accommodate sealants.
Stone by Burlington is more than able to meetthe exacting requirements of the modernconstruction industry, yet retains all the beauty ofa natural material – a characteristic enhanced bysensitive detailing. The stone gives a practical,hard-wearing surface, which will maintain itsappearance over centuries with virtually nomaintenance, other than periodic cleaning.
The intrinsic beauty and quality of Burlingtonstone is clearly visible to building users andpassers-by, enhancing the prestige andsignificance of any building.
REALIZING THE POTENTIAL OF CLADDING
Cladding by BURLINGTON 5
Project: McKenna and Cuneo,Washington DC
Architect: STUDIOS
Cladding to staircase in honed Broughton Moor
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All buildings undergo dimensional changesresulting from:
• settlement
• loading
• thermal effects
Because the physical characteristics andenvironmental exposure of the cladding differfrom those of the substrate, dimensional changesproduced in the one may not be matched bythose in the other. This gives rise to differentialmovement between the cladding and thesubstrate which, if unrelieved, will produce stress,leading to distortion and/or damage.
The risk of damage can be eliminated byintroducing flexible joints between cladding units.These break up differential movement into smallamounts, the joints being wide enough to preventunits coming into contact as a result of differentialmovement. Guidance on how to assess the needfor flexible joints to accommodate expansion andcontraction of the structure is contained inBS 8298: 1994 “Design and installation of naturalstone cladding and lining” and BRE Digest 223,whilst BRE Digests 227, 228 and 229 give detailson how to calculate the extent of structuralmovement.
In principle, differential vertical movementrequires flexible joints at each floor level andabove openings, whilst the management ofhorizontal movement requires at least one flexiblejoint for every 6m (20') length of cladding:additional joints should be sited 1.5 - 3.0m fromeach corner.
The recommended width for flexible jointsaccommodating vertical movement is 10mm(0.375"), whilst flexible joints accommodatinghorizontal movement should be 15mm (0.5")wide. Where necessary the exact dimensions ofthe flexible joints can be calculated by referenceto the anticipated movement, which in turndepends upon the physical characteristics of thesubstrate and the cladding: stone by Burlingtonhas a thermal coefficient of expansion of 10.4 ´ 10-6m/˚C (a 3.0m length undergoing a50˚C temperature rise would become 1.5mmlonger). Burlington’s technical services can assistwith calculations for individual projects.
Any movement joint provision made in thesubstrate must also be carried through thecladding and lining. Cladding units which spanflexible joints must be fastened on only one sideof the joint, and supported, without beingfastened, on the other side.
STRUCTURAL MOVEMENT
6 Cladding by BURLINGTON
Large differential movement
Movement accommodated incombined movementjoints
Cladding supportedat ground level
Cladding supportedat floor level
Floor level
Floor level
Stonecladdingwith nomovementjoints
Stonecladding withmovementjoints belowfloor level
Fastened restraint
Fastened loadbearingbracket
Mo
vem
ent
join
t in
su
bst
rate
Fastened restraint
Supported restraint
Supported loadbearing bracketchannel allows for lateral movement
Treatment of joints
Joints between cladding units can be treated inthree ways:
• All joints left open, as in a rain screen system.The effect of wind and rain penetration uponthe cladding and the substrate must be fullyassessed and the ventilation and drainage ofthe cavity properly detailed.
• All joints sealed as soft joints with flexiblesealant.
• Joints which do not accommodate movementsealed as hard joints and localised movementjoints sealed as soft joints.
Hard joints may be pointed in mortar. For jointsunder 4mm (3/16") wide a 4:1 cement:sand mortaris suitable: above that width the mortar mixshould be weaker to reduce risk of shrinkagecracks as the mortar dries. Lime gauged mortarmay also be used: the longer curing time of limegauged mortar will accommodate some initialmovement and once set it will be stronger thancement mortar.
Sealants
The prime requirement of any flexible sealingmaterial is that it retain its integrity across theentire range of changes of width of the joint.Identifying an appropriate sealing materialinvolves matching the dynamic characteristics ofthe sealant (represented by its MovementAccommodation Factor) to the predictedmaximum and minimum widths of the jointsresulting from differential movements.
Sealants differ in their properties of elasticity(ability to recover size and shape afterdeformation) and plasticity (ability to bestretched continuously and permanently).Those with predominantly elastic properties aresuitable for use with cladding materials with littlethermal inertia which respond rapidly to changesin ambient temperature. More massivecomponents, which react over days or weeks,require sealants with a combination of elastic andplastic properties.
It is essential to provide a sealant backing stripfor sealed joints: the backing strip assists in thecorrect application of the sealant by controllingsealant depth, prevents over-spill at the rear ofthe joint and provides a space into which thesealant can deform when compressed. Furtherguidance on the specification and installation ofsealants is given in BS 6213: 1982 “Guide toselection of constructional sealants”(sealants for projects in the USA should complywith ASTM C920).
The choice of an appropriate sealant and itscorrect application are vital if sealant failure is tobe avoided. A common cause of failure ismigration of fluid from the sealant to the cladding,producing dark banding at joints or streaking onthe face of the cladding. Whilst fluid migrationinitially affects the appearance of the cladding, itmaterially affects the performance of the sealant.
Burlington can advise on specific requirementsfor joint sealants.
Internal joints
Although there is no need to make themweathertight, joints in internal lining can betreated in the same way as those in externalcladding. Where joints are narrow (1-2mm) andthe anticipated movement is minimal, then theycan be pointed with neat cement, tile grout orplaster of Paris.
SEALING AND POINTING
Cladding by BURLINGTON 7
sealant
overlap joint
stonecladding
stonecladding
sealant
non-bondingbacking strip
flush joint
stonecladding
Fixing components are the interface between thesubstrate and the facing. They may be formedof various materials such as stainlesssteel, phosphor bronze, or copperand have two main functions:
• loadbearing: totake the deadweight of thecladding or liningunits:
• restraining: tohold the claddingor lining units inposition and resistcyclic loads suchas wind pressureand suction.
Fixings may be subject to direct, bending, shearand torsional stresses, all of which must beaddressed at the design stage.
Recommended stone dimensions
FIXINGS
8 Cladding by BURLINGTON
H
W
(d)
(t)
(d) T
20m
m
(t)
20m
m
(t)
(t)
(d)
(d)
StoneThickness
T
Min.Thickness
(t)
Min.Depth
(d)
40mm (1.5") 15mm 25mm
External cladding
Less than 3.7m above ground or floor level andcontinuously supported
20mm (1") 7mm N/A
More than 3.7m above ground or floor level
Soffits 40mm (2") 15mm N/A
Internal lining
Less than 7m above ground andcontinuously supported
20mm (1") 7mm N/A
Between 3.7 and 7m aboveground or floor level, notcontinuously supported
30mm(1.25")
12mm 20mm
More than 7m above ground or floor level
30mm(1.25")
12mm 20mm
Soffits 40mm (2") 15mm N/A
Sources: BS 8298: 1994 and (figures in brackets) MIA Design Guide IV.Local building codes and standards may specify other dimensions.
Loadbearing
Loadbearing fixings must beprovided at each floor level andover all openings in the structureor cladding. The load carried willdepend on the thickness andarea of the panels and thedensity of the stone. Cyclical orpermanent water absorption canalso affect the load, butBurlington stone’s low absorptionrate of 0.18% largely eliminatesthis consideration.
Loadbearing is commonlyachieved using recessed anglebrackets set at the bottom of theslab, or corbel plates projectinginto mortices pre-cut into theback of the stone. The requireddepth of recesses and morticesis given in the table opposite.
Combination fixings
Design constraints may requirefixings to be loadbearing whilstalso providing restraint. This canbe achieved by cranking theangle brackets or corbel plates,or by adding restraining dowelsto angle brackets. Combinationfixings should be fastened asclose as possible to the bottomof the stone.
Undercut panel anchors may beemployed where the cladding orlining is to be fixed to a steelsupport framework.
FIXINGS
Cladding by BURLINGTON 9
alternative anglebracket with dowels to
provide restraintsimple boltedangle bracket
alternative corbel plate cranked toprovide restraint, fixed to channel
bolted corbelplate cranked toprovide restraint
angle bracketloadbearing supports
corbel plateloadbearing supports
alternative angle bracket withrestraint, fixed to channel
structural steelwork
panel anchor bolt
undercut panelanchor
Restraint
Restraint fixings maintain facing stonesin position by resisting the action offorces such as wind loading. Thedesign of restraint fixings musteliminate or minimise permanentstresses upon the stones, fixings andsubstrate.
Each facing stone usually requires tworestraint fixings at the top and two atthe bottom, although for small stonesone restraint fixing top and bottom maybe sufficient. To maximise structuralefficiency, restraint fixings should besited at 1/5 points from each paneledge, or at least 75mm from thecorner. The perimeter distancebetween fixings should not exceed1200mm.
The commonest forms of restraintfixings are ties or cramps with dowelswhich project a minimum of 20mm intodrilled holes in the slabs.
The required thickness of stone behindthe dowel holes is given in the table onpage 8. Wire ties, usually of stainlesssteel, may be used to restrain thethinner stones of fascias and linings.
10 Cladding by BURLINGTON
FIXINGS
angle restraint bracket
alternative restraint bracket
grout in tie
alternative corner details
wire restraint
wire corner tie
channel fixed restraint bracket
top edge restraints
top edge and corner restraints
Structural fixing systems
For large scale projects the use of structuralfixing systems may be appropriate. These serveto integrate the cladding into the whole of thefacade including the glazing andinsulation panels.
Structural fixing systems may consist of:
• Grid systems with the panels mounted oncontinuous steel bearings via rebates cut intothe top and bottom edges of the stone.
• Stone cladding units installed in structurallyglazed curtain walls in similar manner to glass.
• Stone cladding units installed in glazingchannels of glazed curtain wall members, insimilar manner to metal spandrel panels.
Specialist advice should be obtained to determinewhether a proprietary system will be suitable foruse with your project.
FIXINGS
Cladding by BURLINGTON 11
grid systemtop support
strut
top anchor
intermediateanchor
claddingjoint
intermediatesupport
bottom support
bearing tape
bottom anchor
bearing tape
attaching clip
cladding
typical layout of grid system
top support
top support
bottom support
bottom support
grid struts
structuralframe
structural glazing gaskets
metal framesurroundingstone claddingand rigidinsulation
glazing gasket
dowel
intermediatesupports
Soffits
Fixings for soffits must bear the load ofthe stone and maintain alignment. Disc bolts located in mortices in thestones both support them and allowadjustment. Other fixing methodsinclude the use of dowelled brackets,or face fixing with bolts passingthrough the stones.
The attachment of fixings
The methods chosen for attachingfixings to the substrate will dependupon the nature of the substrate andthe fixings specified. In all cases thefixings must allow for three wayadjustment to enable the stones to bealigned and levelled correctly.
Individual fixings may be attached toconcrete or blockwork substrates withexpansion bolts or resin anchors, whilstties may be grouted with mortar. Metalchannels which are either cast into orbolted to the substrate may also beused; they are particularly suitable forrestraint fixings, as the fixings canmove to accommodate dimensionalchanges in the stone.
A steel substrate may require asecondary framework to providesufficient attachment points; the risk ofbi-metallic corrosion must be avoidedthrough careful choice of materials andthe use of isolating bushes andwashers.
12 Cladding by BURLINGTON
FIXINGS
soffit fixings
Project: Aronoff Center for the Arts, Cincinnati, USA
Architect: Cesar Pelli andAssociates, New Haven inassociation with GBBN
Cladding to staircase in honed Elterwater
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alternative soffit fixing
The range of design and fixing options is toowide to allow us to offer a draft specification, butthe project specification should cover thefollowing headings:
• Location and extent of cladding or lining.
• Loading conditions.
• Nature of substrate, including supportingstructure, cavity and insulation details.
• Supplier: BURLINGTON
• Stone: *Elterwater;*Brandy Crag; *Broughton Moor;*Bursting Stone;*Blue Grey.
• Finish: *waterjet *honed *sanded *cleft *gritblasted *flamed *textured.
• Dimensions of facing stones.
• Joints: dimensions, material.
• Flexible joints: locations, dimensions, buildingmaterials, treatment/primer/preparation,sealing material.
• Fixings: type and materials.
*delete as appropriate
Burlington’s technical advice service can assist inthe development of working drawings and adviseon fixing plans; manufacturers of proprietaryfixing systems can advise on any specificrequirements.
Grooving and chasing of the stones must bedone at the quarry, the stones reaching site fullyprepared and ready for erection.
Handling and Storage
As Burlington stone is a dense, heavy material,vehicular access should be provided to a storagearea close to the point of installation.Care must be taken on site to prevent damage tothe material; when not crated it should bestacked on edge on timber bearers and protectedwith building paper or plastic sheeting.
Health and Safety
Burlington stone is an inert material andinherently safe if handled with due caution; safe lifting techniques should always be used.Wear protective clothing to avoid cuts from sharpedges. Wear eye protection when machining,drilling or cutting. Dust produced by drymachining contains silica which can be a long-term health hazard if inhaled in significantquantities for extended periods: use a suitabledust mask.
Installation
The type and number of fixings must be inaccordance with manufacturer’s instructions andrelevant standards and building codes. Ensure site work complies with the fixingschemes, otherwise the strength of fixings will becompromised.Clean all dirt, dust and grease from jointingsurfaces. Follow the manufacturer’s instructionswhen applying sealants.Clean down work on completion, using cleanwater and a bristle brush.
MAINTENANCE
Burlington stone is durable and when correctlyfixed requires very little maintenance. Periodicallycheck the effectiveness of compression andmovement joints; renew sealants and pointingwhen they reach the end of their useful life.
Clean with water and mild detergent, finish offwith a chamois leather. For more informationrefer to BS 6270: Pt1: 1982 “Code of practice forcleaning and surface repair of buildings”(MIA Design Manual IV: specification for slate:Part VI).
Cladding by BURLINGTON 13
SPECIFICATION SITEWORK
14 Cladding by BURLINGTON
Prices and conditions of sale
Stone by Burlington is sold subject to ourstandard conditions of sale, a copy of which isavailable on request. We will gladly provide youwith current details of availability and lead timesand will be happy to provide firm quotations forindividual projects on the basis of drawingsand/or Bills of Quantities.
Supply, delivery
Burlington stone is normally crated and palleted:delivery in the UK is by our own road haulagevehicles, overseas deliveries will be by the mostefficient available method.
References
Burlington stone has been used in numerouscladding schemes world-wide, including:-
• Corporate Headquarters, 55 Bishopsgate, London, UK;
• Marugame Museum, Japan;
• Canary Wharf, London, UK;
• Marriot Hotel, Glasgow, UK.
Note
Recommendations as to methods, use ofmaterials and construction details are based onthe experience and knowledge of Burlington SlateLimited and on British Standards: they are givenin good faith as a general guide to designers,contractors and manufacturers.
Quality
Quality comes naturally with a material 400million years in the making and in converting thatmaterial to modern building componentsBurlington operate an ISO 9002 QualityAssurance System.
Whatever the nature of your project, Burlingtonhave the experience, the facilities and theexpertise to provide the guidance, technicaladvice and delivery schedules essential to itssuccess.
Technical support
We are always happy to provide technical adviceon the specification of Burlington stone for newbuild or refurbishment projects. We offer in-depthproject consultation and a wide range of supportservices including:
• a technical advice line: +44 (0) 1229 889 665;USA: (972) 985 9182
• estimating;
• computer-generated detailing;
• copies of relevant test results;
• product samples;
• help and advice on meeting national building regulations.
In addition, a range of technical support materialis available on request; it includes:
• Product Data sheets for the stone from eachof our five quarries.
• Sample cards for all stone tones and finishes.
• Application brochures for:
• Flooring stone;
• Interiors;
• Cills;
• Roofing;
• Burlington Natural Slate Ventilators;
• Landscaping;
• Coping stone.
Our range of stone products is continually beingextended. If you do not find your exactrequirement in this brochure please call ourtechnical advice line. We can probably supply acustomised solution for you.
The applications shown in this brochure shouldnot be treated as limits for the use of stone forcladding: at Burlington we are pleased to assist indeveloping innovative applications for our stone.
Cladding by BURLINGTON 15
PROJECT PORTFOLIO
brochure designed by:JPA Technical Literature, Newcastle upon Tyne
(0191) 281 8393
Project: McKenna and Cuneo, Washington DC
Architect: STUDIOS, Washington DC
Cladding to staircase in honed Broughton Moor
➔
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Project: Barthonia Forum, K�ln, Germany
Architect: Luczak & Jurgensen
Cladding in honed and flamed Elterwater
Project: Canary Wharf, London
Architect: Cesar Pelli
Cladding honed in Elterwater
➔
Burlington Slate LimitedHead Office
Cavendish House, Kirkby-in-Furness, Cumbria, LA17 7UN, EnglandTelephone: 01229 889 661 • Fax: 01229 889 466
e-mail: [email protected]
London Office15 Queen Anne’s Gate, London SW1H 9BU, England
Telephone: 020 7976 7676 • Fax: 020 7976 0033
Web Siteswww.burlingtonstone.co.ukwww.burlingtonslate.co.uk
Soda Hall, University of California, Berkeley CAArchitect: Anshen and Allen in association with Barnes and Cavagnero
Cladding in flamed Broughton Moor
Burlington Natstone Inc.
2701-C West 15th Street, #505, PLANO, TX 75075, USATelephone: (972) 985 9182 • Fax: (972) 612 0847
e-mail: [email protected]