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8.0 UKCSA Standard

This standard has been developed by the members of the United Kingdom Cast Stone Association and surpasses the requirements of the current British Standard BS 1217:2008.

8.1 Scope

This Standard covers the materials that can be used, the acceptable tolerances and minimum performance in terms of strength and durability for cast stone.

8.2 Definition

For the purposes of this Standard the following definitions apply:

Cast stone: Any material manufactured with aggregate and a cementitious binder that is intended to resemble the appearance of, and be used in a similar way to natural stone.  Cast stone is either homogenous throughout or consists of a facing materials and backing material.

For other definitions of concrete materials, reference should be made to BS 6100. 

8.3 Materials

8.3.1 Binders and Binder Constituents

Cast stone shall be made by using one of the folllowing binders complying with the appropriate standard:

BS EN 197-1: 2000       Specification for Portland cement
BS EN 197-4: 2004       Specification for low early strength blastfumace cements
BS 4027: 1996             Specification for sulphate-resisting Portland cement
The binder shall be used either by itself or, for cements complyingwith BS EN 197-1, in combination with one of the following; 
BS EN 15167-1: 2006   Ground granulated blast furnace slag for use in concrte, mortar and grout
BS EN 450:2005           Fly ash for concrete

8.3.2 Aggregates

Aggregates used, apart from grading requirements, shall conform to the appropriate standard as follows:
BS EN 12620: 2002     Aggregates for concrete
BS EN 13055: 2002     Lightweight aggregates for concrete, mortar and grout
BS EN 15167-1: 2006  Ground granulated blast furnace slag for use in concrete, mortar and grout
BS EN 450: 2005         Fly ash for concrete
BS 3892-2: 1996         Pulverised-fuel ash to be used as Type 1 addition

8.3.3 Additives

There are a variety of additives which may be used as an integral part of the cast stone mix.  The two main uses of additives are to improve the plasticity of the mix and to reduce permeability of the finished product.  Self compacting admixtures can be used in the wet cast process.

Plasticisers tend to be chemicals based on compounds of Formaldehyde or Lignosulphate and improve the workability of the ix and aid compaction.  Water proofers can either be a surface treatment or an integral part of the mix.

Surface treatment proofers tend to be based on acrylics, silicones, silanes or siloxanes that can either penetrate the surface to form a chemical bond within the substrate imparting hydrophobic/hydrophilic properties or form a water impervious surface.

Integral water proofers work by either filling the pore structure to block the further penetration of water i.e. hydrophilic or imparting a charge to the pore surface to repel water particles i.e. hydrophobic.

Metal stearates have been used as an integral water proofer for over 50 years.  These stearates are hydrophobic and are typically blended with other materials to obtain good dispersion within the cement matrix.

Calcium stearates are used primarily as damp proofers, where an electrostatic charge is imparted into the walls of the capillaries of thecast stone mix.  By the very way in which these strearates are produced, they also have the added advantage that they act as water proofers by sealing the voids within a macro texture of the materials.

8.3.4 Pigments

Metallic Oxide pigments used in the manufacturing process should conform to BS EN 12878: 2005 Specification for Pigments for the colouring of building materials based on cement and/or lime.

8.4 Requirements for Units

The declaration of the properties of the units called for in this Standard will assist the designer in correctly designing the construcition works.

All requirements for testing of products detailed within this section are further defined in Appendix 1 & 2.

For Internal Quality Control, other test methods may be used provided that:
  • A relationship can be shown to exist between the results from the standard test and those from the alternative test, and
  • The information on which the relationship is based is available for inspection.

8.4.1 Two Part Mixes

When cast stone is made from separate facing and backing mixes the facing shall have a minimum thickness of 20mm at any point.  A bond between the facing and backing mixes shall be made either by a mechanical key or by inter-diffusion.

8.4.2 Surface Finish

Surface finishing techniques may be employed in the manufacture of cast stone.  The surface finish shall, unless otherwise specified, exhibit a texture similar to that of natural stone.  The colour and texture of the exposed (when installed) face of cast stone should be agreed between the supplier and the purchaser.  The supplier and the purchaser.  The supplier should on requrest supply a sample of an agreed size for approval of the purchaser.  It is important that finishes are discussed with the manufacturer, particularly where very smooth surfaces are being considered, as the type of finish will significantly influence the overall appearance.

8.4.3 Liner Dimensions

The actual dimensions of individual regular units should conform to the declared work dimensions subject to the tolerances given below.  Individual manufacturers may specify tolerances that are tighter than those in the table following page.
Dimensions(mm)     Tolerance (mm)
up to 600                +/- 2
601 - 1000              +/- 3
1001 - 2500            +/- 4
2501 - 4000            +/- 5
over 4000               +/- 6

8.4.4 Flatness of Plane Surface

Where the surfaces intended to be exposed in the finished cast stone are declared by the manufacturer to be plane, they shall not deviate from a plane by more than the values given below.  The units shall be tested in accordance with Appendix 1.

Maximum permitted variation from plane = 0.3% of the maximum dimension of the item or 2 mm whichever is the greater.

8.4.5 Slenderness Ratio

Slenderness ratio is equated by using the diameter of either an inscribed or superscribed circle on the section of the product, determined by the supported plane, and the length of the product:
The slenderness ratio SR is given by the equation: SR =  L/d where L is the product length in mm and d is the diameter of the circle.

The slenderness ratio should be less than or equal to 15 for wet cast units or less than or equal to 12 for semi-dry units.

Alternative ratios may be used subject to agreement between manufacturer and purchaser and slenderness ratio is not relevant in the case of thin walled Fibre Reinforced Cast Stone (FRCS) units with their enhanced tensile and bending strength. 

8.4.6 Reinforcement

For structural elements consideration must be given to the design strength and the reinforcement detailing.  Reference should also be made to BS EN 1992 BS EN 1996.  Alternatively, advice should be sought from the individual manufacturer.

Untreated low carbon high yield steels shall have a minimum cover of 40 mm when measured from any installed exposed face and 30 mm from any protected face.

Glavanised steels shall have a minimum cover of 30 mm when measured from any installed exposed face and 20 mm from any protected face.

Stainless steels shall have a minimum cover of 10 mm or twice the bar diameter whichever is the greater, when measured from any exposed face.

For other reinforcement materials the specification is as given in BS 1217: 2008.  A variety of other reinforcement materials such as basalt fibre or fibre reinforced polymer product are available and their use will be drawn to the clients attention prior to manufacture of the units.

Cut end of galvanised steels must be coated before use.

Where units are made from two-part mixes, reinforcement shall neither be placed within 10 mm of the interface nor across the interface of the facing and backing mix, unless the cementitious binder used in both mixes is identical.

Reinforcement may be required either for structural or handling purposes only.  Other metal components may be required for fixing or restraint purposes.  These may or may not be considered as part of the reinforcement.

8.4.7 Compressive Strength

The average crushing strength of three cubes tested to BS EN 12390-3 shall not be less than 35 MPa @ 28 days old.  No individual cube is to have a strength of less than 28 MPa.

The figure of 35 MP a represents a 40% increase in compressive strength over that indicated in the British Standard and is as a result of research carried out by The University of Dundee.  Note: 1MPa is equal to 1N/mm2.

8.4.8 Capillary Absorption Test (CAT)

When sampled and tested in accordance with Appendix 2 with an immersion time of 10 minutes, the mean coefficient of water absorption due to capillary action of the three samples shall not exceed 1.0 mg/mm2 with no individual value exceeding 1.3 mg/mm2.

It should be noted that the recent research project undertaken in conjuction with the The University of Dundee has identified that the overall durability of a product is more likely to be indicated by the compressive strength than the CAT figure.  The CAT figure is more useful in determining whether a water proofing/damp proofing additive has been included.

8.4.9 Sulphate Resistance

Where sulphate resistance is required (normally in unprotected ground or ground containing natural sulphates) the suitability of the units shall be based on the cement type and content.

8.4.10 Thermal Conductivity

When requested by the customer, the manufacturer/supplier shall declare the thermal resistance of the units.  The value shall be established either by testing or from recognised tables.

8.4.11 Fire Properties

Units manufactured in accordance with this Standard are non-flammable, non-combustible, do not give off toxic gases and can provide a barrier to the spread of smoke and flame.  Standard values should be referred to for the fire resistance of walls made from units complying with this Standard. 

8.4.12 Sound Insulation

The sound insulation provided by cast stone built with units to this Standard is predominantly influenced by mass per unit area.  The density of the units will be declared by the manufacturer on request to enable mass calculations to be carried out. 

Other factors such as the shape of the units and the air-tightness of the wall also have an influence.  In general, the sound insulation of a cavity wall is affected by the width of the cavity, the type and sapcing of the wall ties.

8.5 Sampling

8.5.1 Cube Crushing Test

Compliance testing shall be demonstrated by the testing of three cubes of either 100 mm or 150 mm size made from the facing mix and also from the backing mix where applicable.  The three cubes shall be made from a single batch of mix and shall be compacted in the same way as the finished cast stone.  Compliance testing shall be carried out on a minimum of a weekly basis. 

8.5.2 Capillary Absorption Test

Select three samples of cast stone (when tested these must be at least 17 days old).  The sawing of specimens shall not be permitted.  Capillary absorption testing shall be carried out on a minimum of a quarterly basis. 

8.5.3 Marking

The following particulrs shall be clearly marked on the delivery notes, drawings or supplier's certificate supplied with a consignment of cast stone products:
  • The name trade mark or other means of identification of the manufacturer.
  • Product reference and/or description.

To comply with BS 1217: 2008 the manufacturer must also clearly state the weathering class i.e. either CAT and/or ISAT and the number and date of the British Standard (i.e. BS 1217: 2008).

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