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MANUFACTURERS OF ARCHITECTURAL TERRA COTTA _ FAIENCE STANDARD

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MANUFACTURERS OF ARCHITECTURAL TERRA COTTA _ FAIENCE STANDARD Powered By Docstoc
					          MANUFACTURERS OF ARCHITECTURAL TERRA COTTA & FAIENCE
                             EMAIL: sales@HathernTerraCotta.com

           www.HathernTerraCotta.com Tel 00 44 1509 843302 Fax 00 44 1509 507566

STANDARD SPECIFICATION OF THE MANUFACTURE & USE OF ‘HATHERN’ GLAZED
              OR UNGLAZED ARCHITECTURAL TERRA COTTA

1.0   DEFINITIONS

1.1   Architectural Terracotta (alts:Terra-cotta, Terra cotta)- a ‘body’ of selected and
      prepared clays made plastic by the addition of water, hand pressed into moulds,
      dried, finished and fired in a kiln to make hard and durable. Blocks are generally
      of a size and shape which exceeds that of brick, e.g. 450mm long x 215 x 300
      high. used in load-bearing masonry construction. Blocks can be either ashlar,
      moulded, enriched or ornate. Different colours are typically earthy, e.g. Red, buff,
      tawny, grey, etc.

1.2   Architectural Faience - all as terra-cotta but with the addition of a surface
      coating of either a ‘glaze’ or ‘engobe’, typically a different colour and texture to
      the underbody.

1.3   Body - Clay, or blend of clays, prepared to the required consistency from which
      certain elements and impurities have been removed and to which selected
      constituents may have been added, i.e. mineral stains and metallic oxides.

1.4   Glaze - A coloured coating, either opaque or translucent, applied to clay blocks
      or slabs which when fired become a hard and durable finish. Glazes can be plain,
      mottled or textured and can range from high gloss to egg-shell finish.

1.5   Engobe - an opaque, coloured clay slip coat applied to the surface of a block or
      slab and fired to a hard and durable finish

1.6   Hand pressed block - a load bearing unit, either Terra-cotta or faience, formed
      by building clay walls approx. 35mm (11/4") thick. Hollow cells are formed in the
      back of the block by the addition of strengthening webs. They can be straight,
      curved or circular Blocks fall into the following categories.

      •       Ashlar - a block of rectangular shape with one or more finished faces. I.e.


Hathern Offices, Hathernware Industrial Estate, Rempstone Road, Normanton on Soar, Loughborough,
                                      Leicestershire, LE12 5EH

                             Part of Charnwood Forest Brick Limited

                                    Registered No 03690069 England
              ashlar quoin; two faces, ashlar double quoin; three faces.

       •      Moulded - a block with a uniform linear profile along one or more faces.
              E.g. string, cill, cornice, etc.

       •      Enriched - an otherwise ashlar or moulded block with the addition of a
              simple sculpted decoration pattern. E.g. egg & dart, acanthus leaf, etc.

       •      Ornate - a block bearing a complex piece of free hand sculpture e.g. coats
              of arms, statuary, urns and vases, etc.

1.7    Extruded block - linear units of either ashlar or moulded description machine
       formed by forcing clay around a shaped die. Continuous voids may also be
       formed in the process in the direction of extrusion.

1.8    Slab - A non load bearing unit, either terra-cotta or faience, in the range of 40 to
       75mm thick made by either pressing, extrusion or casting, used as a cladding to
       a structural wall. Mechanical, non ferrous, fixings are required to provide support
       and restraint. Typically units are up to 750 long (depending upon thickness) x
       300mm wide and are cut to length and height after firing.

1.9    Firing - Clay, in the blocks or slabs, are subjected to high temperature in a
       controlled environment kiln using gas or other fuels. Optimum firing temperatures
       depend on the clay and glazes used. Typically temperatures around 12000c are
       achieved to make the units hard and durable. With Architectural Faience it is
       sometimes necessary to twice fire the units as some glazes mature at lower
       temperatures than the body.

1.10   Efflorescence - is the gradual migration of soluble salts, which are sometimes
       present in clay bodies, mortars and fill, being drawn to the surface of the block by
       the climatic action of wetting and drying then crystallizing and forming white
       deposits.

2.0    PHYSICAL PROPERTIES OF CLAY BODIES

2.1    Compressive Strength - Of the material is generally greater than 40 N/mm2
       when tested in accordance with BS 3921:1985. Typically a strength in the range
       of 50-70N/mm2 can be anticipated.

       Note: the ultimate failure strength of a block should not be confused with the
       compressive strength of the body from which it has been made. For example an
       ashlar block made from a fired clay body of 75N/mm2, 450mm long x 100mm
       deep x 300mm high, with walls and webs of approx.30mm thick and unfilled
       hollow voids when tested to destruction failed at 25N/mm2 approx. We disregard
       the effect of any concrete filling in the voids as, due to shrinkage, it can not be
       guaranteed to perform structurally.
2.0   Frost resistance - Classified in the 'F' category of BS 3921:1985

2.1   Liability to efflorescence - Due to the high temperatures and long firing cycles
      generally employed in the production of Architectural terra-cotta and Faience
      their liability to efflorescence can generally be assumed to be ‘low’ to ‘nil’ when
      tested in accordance with BS 3921:1985. However certain clays together with low
      firing temperatures necessary to achieve required colours may cause the units to
      exhibit a tendency towards efflorescence. It should also be borne in mind that the
      presence of soluble salts in the cements, aggregates and sands used in the
      installation can contaminate Terracotta and Faience causing efflorescence.

2.2   Thermal Conductivity.. 0.5-0.9 Wm/0c dry (k value) 1-1.5 Wm/0c @ 5% moisture

2.3   Fire resistance - Incombustible

2.4   Acid resistance - Not adversely affected by atmospheric pollutants.
      Susceptible to damage in contact with Hydrofluoric acid.

2.5   Bulk Density - Generally in the range of 1900-2750 kg/m3

2.6   Water absorption - Generally in the range of 3 to 15% by volume when tested in
      accordance with B.S. 3921:1985

3.0   PHYSICAL PROPERTIES OF GLAZES AND ENGOBES

3.1   Craze resistance - To comply with the requirements of B.S. 6431: Part 17

3.2   Surface hardness..... Between 4-7 on Moh's scale of hardness

      Note: The ability of a glaze or engobe to resist crazing is very much dependent
      upon the constituents in its make up. Where a specific colour is required, e.g.
      restoration work or meeting design requirements it is not always possible to meet
      the requirements B.S. 6431 : Part 17. Even if a glaze is deemed to be ‘craze
      resistant’

4.0   MANUFACTURING TOLERANCES

4.1   Overall size - +/- 2% in linear dimensions

4.2   Twist - 5mm per 300mm measured across the diagonal

4.3   Out of Square - 5mm per 300mm length

4.4   Colour... to be in keeping with the body or glaze sample submitted. As with all
      clay based products shade variations are to be expected. The range of which is
      dependent upon the materials used and firing temperatures required.

4.5   Surface Quality... units are to be free of imperfections which are known to have
      an adverse effect on the durability of the finished product. Visual imperfections,
      such as pin holes, crawls, minor copper spots, etc., are permissible provided they
      do not detract significantly from the overall appearance of the work when
      inspected at normal viewing distances.

5.0   PACKING AND DELIVERY

5.1   Domestic - units are to be packed with either polystyrene or woodwool on non-
      returnable timber pallets and shrink wrapped. Delivery will be made by flat bed
      lorry, size to suit load and site conditions, with crane off-loading if requested.
      Carriage, packing and handling is charged extra unless otherwise stated.

5.2   Export - units are packed in timber crates with polystyrene or woodwool packing.
      Any import restriction on use of packing materials imposed will be taken account
      of. Shipping or air freight can be arranged as required which will be charged as
      an extra unless otherwise advised. Insurance's, taxes and local duties can be
      allowed for to suit customer requirements.

6.0   SITE WORK

6.1   Acceptance on site - Units are to be checked upon delivery comparing the
      reference numbers imprinted in a bed face against the delivery notes supplied
      and any discrepancies reported. If pallets are to be set aside, unopened, for later
      use a suitable and secure storage area is to be provided to prevent any 3rd party
      damage. Upon unwrapping pallets any units thought not to be in compliance with
      manufacturing tolerances are to be advised to us in writing and set aside for
      collection or inspection. Units damaged in transit will be replaced free of charge,
      in accordance with our conditions of sale, provided that the blocks have not been
      filled with concrete or installed on the building.

6.2   Check outs - used to maintain the shape of the unit during firing are to be
      carefully removed by the fixing contractor prior to filling and installation.

6.3   Void filling (non structural) - The hollow cellular voids of the blocks are
      traditionally filled with concrete. Unless the concrete fill is expected to provide
      structural strength it is our recommendation that the following specification be
      used.

      8:1 sand/cement with clean broken brick aggregate trowel filled into voids and
      not otherwise compacted.

      A light weight fill based on the use of 'Light-Ag' is satisfactory under normal
      conditions provided that the possibility of being the potential cause of
       efflorescence has been fully discounted.

6.4    Void filling (structural) - Where a need for the concrete fill to provide structural
       strength has been identified by the structural engineer caution during filling
       should be exercised. Any potential problems due to stresses caused by thermal
       expansion of the fill during setting should be fully accommodated

6.5    Permanent Shuttering - It is not our recommendation that blocks are used as
       permanent shuttering in cast in situ structural concrete elements.

6.6    Setting out - due to the potential of inherent size and variation of units it is
       important to establish the best setting out of features before commencing
       installation. Joint sizes should be expected to vary to some extent to assist in
       accommodating manufacturing tolerances. Where necessary units can be
       trimmed on site by the fixing contractor to achieve a satisfactory fit.

6.7    LAYING - traditionally terracotta blocks were set with a mortar joint nominally
       4mm wide, this being subject to +/- variations due building and manufacturing
       tolerances.

6.8    Mortars - the selection of the type of mortar to be used is dependent on various
       factors. For example:-

       •      matching existing mortars (Restoration projects)
       •      colour of mortar required (To match existing or design requirements)
       •      construction (e.g. cladding or load bearing)
       •      structural considerations, solid masonry, steel frame construction, etc.

       Whilst traditionally a strong mortar would have been specified 3:1 sand/cement
       current practices favour a weaker mix more capable of accommodating building
       movement. The specification of the type of mortar to be used is therefore a
       matter for the architect and structural engineer to decide.

6.9    Preparation -
       • Units should be checked for fit and any adjustments, i.e. cutting, made.
       • Units are to be filled 24 hours prior to installation allowing for the fill to cure.
       • Units should be wetted, not soaked, at the time of laying.

6.10   Fixings - Generally in stainless steel provide bearing and restraint. Any structural
       design requirements are the responsibility of the supplier or the structural
       engineer. Any existing ferrous metals are to be treated to prevent possible
       damage to the terra-cotta due to corrosion.

6.11   Cleaning down
       Units are to be washed down during installation. Any mortars stains, etc. are to
       be washed off as work progresses. Chemical cleaning compounds are to be
      avoided unless professional advice on their use has been sought. Compounds
      containing hydrofluoric acid are known to damage terra-cotta and must not be
      used.

7.0   MAINTENANCE

7.1   Visual inspection - Should be carried out on a regular basis and any failure of
      joints rectified. Associated works such as flashings, lead dressing, asphalt roofing
      should be checked for signs of deterioration. Any weep holes incorporated in the
      units should be rodded clean to prevent water retention in the fabric of the
      building.

7.2   Cleaning - Specialist advice should always be sought before undertaking any
      cleaning work. The avoidance of damage to the terra-cotta should be the primary
      consideration. If possible compounds containing Hydrofluoric Acids should be
      avoided.


8.0   SUMMARY

8.1   Compliance with relevant British Standards, specified tolerances, etc. - It is
      sometimes more important to achieve a good aesthetic match, for example
      restoration work, than specific physical properties and tolerances. In the event
      that adjustment to the body or glaze is required to achieve stated properties or
      tolerances, this may require some compromise in other regards, i.e. colour and
      glaze finish.

8.2   Testing - Where specific requirements are stated we would undertake to carry
      out tests to confirm compliance either at our own testing facility or by other
      independent means. Any requirement for testing should be advised to us prior to
      submitting our quotation so that costs can be included and our manufacturing
      programme formulated accordingly.

				
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