Litos - Dimension Stone Standards

Asher Shadmon

Standardisation of commodities besides providing a technical code is one of the cornerstones on which world trade is based and has received increased attention since the creation of the EU. Not that the subject is new. As a matter of fact ASTM (American Society for Testing and Measurement) was established in 1898 and the National Institute of Standards and Technology (NIST a branch of the USA Department of Commerce) has observed last year the 100th anniversary of their agency.

Workmanlike results were turned into rules of quality. This eventually led from compliance with technical product specification to checking and certifying the production process - altogether giant steps as a stone industry known for its traditionalism. So when CEN (Centre Europeene de Normalisation) was born in the early 1960's European standardisation activity started to unify or harmonise national norms into "European".

Whereas the standardisation of manufactured goods and for that matter agricultural products can be controlled to a certain extent, stone materials are nature's creation and standards have to be adapted to the materials available. This is the more difficult because of the globalisation of the world trade in stone with supplies of large variability range. In addition standards are subject to planning regulations which vary from country to country, with an almost infinite variety of local governments and authorities.

Degrees of resistance to weathering, weakening of stone by ageing and the multitude of environmental factors are not always apparent in the stone standards. These do not always pay attention to the stone varieties available. Notorious in this respect is the standards that refer to stone without specifying in detail the petrographic properties of stone. The justification argued is that standardisation is directed towards the end use of the product. Whereas in manufactured materials safety standards can be included in the planning, this is more difficult when applied to natural stone.

Confusion starts with the legal position of standards, the connection between those assuring public safety (and health) and standards which contain technical requirements i.e. solutions for engineering problems. Preventing of using alternate solutions hobbles technical development.

Originally standards provided guidelines for manufacturers and were not intended to be compulsory or legally binding. Only in cases where the standards are specified in legal documents mutually agreed by the supplier and user, these have a legally enforceable status. The recently promulgated European Standards coded EN (European Norm) are designed to protect consumers while taking into consideration the suppliers' possibilities. Without this approach, based on the mutual recognition of standards global trade would be chaotic, taking into account the variation of practices.

The European regulations are based on strict procedures not only to develop the standards but also to approve the standards. Working groups follow the procedures before they are passed through various stages leading to adoption and acceptance by the EU member countries follows the procedures.

Although the EU Standard activities made a start in 1985, the work on the stone standards started to develop in the early 90's when a veritable network of working groups was established and their findings co-ordinated at plenary sessions of several groups working on stone matters. Specialized working groups are part of Technical Committees and other related groupings may be invited to these plenary sessions. Dimension Stone is dealt mainly by CEN 246.

The sister groupings include CEN TC 125 WG1 TG6 dealing with manufactured masonry units, not essentially natural stone, CEN TC 128 SC with slate and stone products for discontinuous roofing and cladding, CEN TC 154 SC4 with aggregates and armour stone, and CEN TC 178 WG2 which deals with slabs, setts, and kerbs for external paving.

There are 3 types of standards dealt with by CEN 246 Natural Stones: Terminology and General, Test Methods and Product Standards, their progress status is attached. The Test Methods rather than Product Standards are the common denominators of the groups.

Whatever the present stage of acceptance, the deadline for the CE marking of building products in stone is March 2004. The CE mark comes together with a certificate of conformity covering the declaration of conformity by the manufacturer. Such a declaration presumes a series of tests carried out to as certain petrographical, physical and application characteristics in addition to denomination and the use of standard technology.

An array of engineers, architects, scientists and representatives of the industry, the majority being connected with the standards testing institutions, work on the standards in the working groups. The influence of existing national standards and practices is felt during the discussions and resultant standards are based on compromises. The most intricate compromises, which surface during the decisions on the Product Standards (Group 3), are in a sense summarising the results of the other 2 groups. These include the specifications for rough blocks (EN 1467) rough slabs (EN1468), slabs for cladding, (prEN 1469), dimension stone work (prEN 12059). Another Product Standard, kitchen and vanity tops, is under consideration by TC 246 and will be given a prEN denotation in due course.

Compromises are not only on country basis but often these are reached between the various technical disciplines and practical experiences. This is particular true in the terminology groupings of stone varieties.

The experiences of natural stone users are fed to the standardisation committees for analysis and inclusion, to improve the system. This enables continuity and perfection of application of the stone at its final destination and is important when deciding which tests to use, taking into consideration environmental factors.

CEN/TC 246 is working on more than 30 standards. Of all these a few relevant standards are used for each application depending on use, type of stone and environmental factors. E.g. abrasion tests are superfluous for cladding and aging by salt mist tests for enclosed interior use

A complete terminological jargon has evolved around the standardisation efforts. Technical Standards serve to define products and how to check them c.f. "good technique rules" as defined by civil law). The standards as defined by CEN have a voluntary content binding the parties involved and can be quoted as a "de facto", if not legal precedence in court. The regulating or "standardised content" is in the spirit of European Directive 89/106 on "Building Products" and has manifold meanings. It is a declaration of standard's compliance with the directive, and refers to the control criteria during the tests, the information required for the EC mark.

Initials used include EN for European Norm; prEN for not yet approved EN and WI, work item, followed by a number, denotes the initial drafting stage. The prefix hEN, occasionally used, stands for a harmonised EN Standard. TC=Technical Committee.

The tests for the working groups are generally available in English, French and German. After final approval national standardisation authorities may translate the standards in their own language.

Up to the end of 2001 twelve Test Methods were approved and published. There are now nine under approval scheduled to be ratified up to September 2003 and three under study. Six Product Standards are under approval with expected availability before end 2002. Two Work Items (WI) are presently considered for further study by CEN TC 246.

Besides stating the purpose, scope, standard references, definition prerequisites, marking and packing described within the main text of the published standards, there may be a number of appendices. These describe the initial tests on the stone materials, usually performed at an independent laboratory and the tests done during processing by the producer himself, to be made available to supervising parties in addition to sampling procedures, identification, markings etc.

The major innovation in the CEN standards in contrast to the traditional BS, DIN, ASTEF, and other national standards is that they are geared to evaluation of conformity and factory production control. It is now required that the supplier or manufacturer of dimension stone products shall be responsible for the assessment and attestation that the products offered are in conformity with the requirements of European standards. The compliance with the requirements of the published standards and stated values, initial type testing and permanent production control, with registration of result have to be made available.

No doubt the cost of control will affect profitability in the competitive stone trade with credibility often at a premium, especially for the smaller producers. Nevertheless compliance with all its obligations will prove to be a blessing in disguise by increasing the much needed consumer confidence.

EUROPEAN CEN DIMENSION STONE STANDARDS

TERMINOLOGY AND GENERAL STANDARDS

EN 12440, Oct 2000 Denomination criteria Published WI 246029

EN 12670, Dec 2001 Terminology Published WI 246004

TEST METHODS

EN 1925, Mar 1999 Determination of water absorption coefficient by capillarity Published WI 246006

EN 1926, Mar 1999 Determination of compressive strength Published WI 246007

EN 1936, Mar 1999 Determination of real density and apparent density and of total and open porosity Published WI 246005

EN 12370, Mar 1999 Determination of resistance to salt crystallisation Published WI 246034

EN 12371, Oct 2001 Determination of frost resistance Published WI 246034

EN 12372, Mar 1999 Determination of flexural strength under concentrated load Published WI 246008

EN 12407, May 2000 Petrographic examination Published WI246013

EN 13161, Oct 2001 Determination of flexural strength under constant movement Published WI246037

EN 13364, Nov 2001 Determination of breaking load at dowel hole Published WI 246010

EN 13755, Dec 2001 Determination of water absorption at atmospheric pressure Published WI 246036

13373 Determination of geometric characteristics Under approval WI 246031

13919 Determination of resistance to ageing by SO2 action in presence of humidity Under approval WI 246033

14066 Determination of thermal shock resistance Under approval WI 246016

14146 Determination of dynamic elastic modulus by measuring the fundamental resonance frequency Under approval WI246035

14147 Determination of resistance to ageing by salt mist Under approval WI 246032

14157 Determination of the abrasive resistance Under approval WI 246014

14158 Determination of rupture energy Under approval WI 246019

14205 Determination of knoop hardness Under approval WI 246015

14231 Determination of the slip resistance by means of the pendulum tester (friction) Under approval WI 246017

Determination of thermal dilation coefficient Under study WI 246011

Determination of sound speed propagation Under study WI 246012

Determination of static elastic modulus Under study WI 246016

Determination of radiation WI to be approved by TC 246

PRODUCT STANDARDS

1467 Rough blocks, specifications Under approval WI 246020

1468 Rough slabs, specifications Under approval WI 246021

1469 Slabs for cladding, specifications Under approval WI 246024

12057 Modular tiles, specifications Under approval WI 246022

12058 Slabs for floors and stairs, specifications Under approval WI 246028

12059 Dimensions stone work, specifications Under approval WI 246025

Kitchen and vanity tops WI to be approved By TC 246

Explanation of the columns:
The first column denotes the coding with publication date where relevant, the middle column the title of the Standard and the third and last column the availability status together with their previous code while still being work items and marked with the prefix WI.

EN=European Norm. The prefix prEN denotes the drafts in their final stages whereas Wi denotes Work Item and indicates drafts in preparation or in the early stages of the approval process.

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Last Updated: July 2008