SIST EN 13815:2006

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Fibrous gypsum plaster casts - Definitions, requirements and test methodsProduits en staff - Définitions, prescriptions et méthodes d'essaiFormteile aus faserverstärktem Gips - Begriffe, Anforderungen und PrüfverfahrenTa slovenski standard je istoveten z:EN 13815:2006SIST EN 13815:2006en91.100.10ICS:SLOVENSKI
STANDARDSIST EN 13815:200601-november-2006

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13815August 2006ICS 91.100.10 English VersionFibrous gypsum plaster casts - Definitions, requirements andtest methodsProduits en staff - Définitions, prescriptions et méthodesd'essaiFormteile aus faserverstärktem Gips - Begriffe,Anforderungen und PrüfverfahrenThis European Standard was approved by CEN on 19 June 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13815:2006: E

Sampling procedure for testing.44 Annex B (normative)
Design values of thermal conductivity of gypsum plaster.46 Annex C (normative) Factory Production Control (FPC).47 Annex ZA (informative)
Clauses of this European Standard addressing essential requirements or other provisions of EU Directives.52 ZA.1 Scope and characteristics concerned.52 Product : fibrous gypsum plaster casts.53 Intended uses : see clause 1.53 ZA.2 Attestation and declaration of conformity of fibrous gypsum plaster casts.54 ZA.2.1 General.54 ZA.3 CE marking and labelling.58 Bibliogaphy.60

The fibrous gypsum plaster structures are made by assembling these casts together and fastening them by sealed fixing or screwing to the substrate. They are then sealed and pointed to form continuous surfaces without any visible joint. Fibrous gypsum plaster structures are suitable for finishing with direct surface decoration (e.g. paints). The diagram below shows the family of gypsum products.
Diagram – Family of gypsum products

This European Standard is applicable to: - conventional series produced products; - series produced products with varying properties ; - individual (and non-series) produced products, insofar required to be CE marked. See 4.1 and annex D concerning the classification of the fibrous gypsum plaster casts. This European Standard covers the following performance characteristics of the fibrous gypsum plaster casts : reaction to fire, thermal resistance, as well as resistance to impact by a hard steel ball and cohesion. The following performance characteristics are linked to systems assembled with fibrous gypsum plaster casts : fire resistance, impact resistance, direct airborne sound insulation, acoustic absorption to be measured according to the corresponding European test methods. If required, tests have to be done on assembled systems simulating the end use conditions. This European Standard defines the reference test methods for the technical specifications. This European Standard also covers additional technical characteristics of fibrous gypsum plaster casts that are of importance for use and acceptance of the products by the building industry and the reference tests for these characteristics. It provides for assessment of conformity of the products to this standard. This standard does not apply to:
i)
fibre reinforced gypsum sheet products (see pr EN 15283);
ii)
gypsum elements for suspended ceilings (see EN 14246);
iii) solid casts;
iv) run fibre reinforced products;
v)
plaster based stucco casts, carton pierre decors, resin decors;
vi)
moulds, models and mock-ups made of fibrous gypsum plaster;
vii) fibrous gypsum plaster casts that, by nature, are not intended to be fastened in position;
viii) fibrous gypsum plaster casts for sets (theatre, cinema, TV);
ix) fibrous gypsum plaster casts and decors intended to be installed directly on existing partitions, walls and ceilings, for purely decorative applications.

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 635-3:1995, Plywood — Classification by surface appearance. — Part 3: Softwood. EN 1611-1:1999, Sawn timber —- Appearance grading of softwoods — Part 1: European spruces, firs, pines and Douglas firs. EN 10327, Continuously hot-dip coated strip and sheet of low carbon steels for cold forming — Technical delivery conditions. EN 10244-2, Steel wire and wire products —- Non-ferrous metallic coatings on steel wire — Part 2: Zinc or zinc alloy coatings. EN 12524, Building materials and products — Hygrothermal properties — Tabulated design values. EN 13501-1, Fire classification of construction products and building elements — Part 1: Classification using test data from reaction to fire tests. EN 13501-2, Fire classification of construction products and building elements — Part 2: Classification using data from fire resistance tests, excluding ventilation services. EN 20140-9, Acoustics — Measurement of sound insulation in buildings and of building elements — Part 9: Laboratory measurements of room-to-room airborne sound insulation of a suspended ceiling with a plenum above it. EN 13279-1, Gypsum binders and gypsum plasters — Part 1: Definitions and requirements EN 13658-1, Metal lath and beads — Definitions, requirements and test methods — Part 1:
Internal plastering. EN ISO 140-3, Acoustics — Measurement of sound insulation in buildings and of building elements — Part 3: Laboratory
measurements of airborne sound
insulation of building elements (ISO 140-3:1995). EN ISO 354, Acoustics — Measurement of sound absorption in a reverberation room (ISO 354:2003). EN ISO 717-1, Acoustics - Rating of sound insulation in buildings and of building elements — Part 1: Airborne sound insulation (ISO 717-1:1996). EN ISO 6946, Building components and building elements — Thermal resistance and thermal transmittance — Calculation method (ISO 6946:1996). EN ISO 10456, Building materials and products — Procedures for determining declared and design thermal values (ISO 10456:1999).
ISO 7892, Vertical building elements — Impact resistance tests — Impact bodies and general test procedures

3.1.2 fibrous gypsum plaster interior architectural cast cast of any shape and configuration, intended for interior architectural works such as volumetric ceilings, vaults, shaped wall linings, porticos.
3.1.3 fibrous gypsum plaster technical function cast cast of any shape and configuration that have technical functions such as shafts for smoke extraction, metal structure fireproof casings.
3.1.4 fibrous gypsum plaster unit (or fibrous plaster slab) flat rectangular fibrous gypsum plaster casts for works such as flat suspended ceilings
3.2 Technical terms and definitions
3.2.1 face surface of the cast intended to be exposed when installed
3.2.2 back surface of the cast intended to be concealed when installed
3.2.3 edge boundary of the cast
NOTE Edges can be square or bevelled (see Figures 1and 2) and can include reinforced rims and/or rebates for surface jointing (see Figure 3)
3.2.4 thickness distance between the face and the back of the cast
NOTE The thickness of the cast is generally constant but can show possible reinforced rim edges or complementary reinforcements.
3.2.5 minimum thickness minimum thickness dimension required for the whole of a cast
3.2.6 nominal thickness contractual thickness or thickness declared by the manufacturer and given in the designation of a cast

NOTE
There are two types of reinforcements defined by their functions:  elementary reinforcements;  complementary reinforcements. 3.2.8 elementary reinforcement initial reinforcement distributed throughout and fully integrated into the cast (e.g. hessian) 3.2.9 complementary reinforcement in some casts, additional reinforcements integrated into or on
the product (e.g. lightweight steel sections) 3.2.10 prime layer (or fibrous plaster firstings) face layer of plaster, without reinforcement 3.2.11 cavity small hollow in plaster, caused by possible air bubbles 3.2.12 handling framework separate component used to provide temporary rigidity and/or support to products during removal from its mould, handling and assembly, usually removed after use (see Figure 4) 3.2.13 wad (or fixing pad) scrim comprising natural fibres usually jute or sisal fully impregnated and coated with plaster and extended to form a grip or handle (see Figure 4) Glass fibres may be used (long fibres, weave or mat). 3.2.14 fibrous plaster rope long scrim comprising natural fibres usually jute or sisal, or strip of hessian, fully impregnated and coated with plaster and extended to form a grip Glass fibres may be used (long fibres, weave or mat). 3.2.15 developed area total measured and/or calculated area of the cast face 3.2.16 surface mass mass per square metre of developed area 3.2.17 GRG cast (glass fibre reinforced gypsum) specific product made from plaster – calcium sulfate hemihydrate alpha based or specially modified beta based - mixed with water and in which the reinforcement is glass fibre

(see Table 1); w index which indicates presence of complementary reinforcement by softwood lath, e.g. f 3w (see Table 2); ρ density in kilograms per cubic metre (kg/m3); λ23-50 thermal conductivity of the product when in equilibrium at 23 °C and 50 % relative humidity in Watts per metre per Kelvin (W/m.K); M mass in kilograms; Mc moisture content; Ad developed area in square millimetres (m2);
GRG see 3.2.17
PMGRG see 3.2.18.
ITT initial type test
FPC factory production control

Key 1 Thickness 2 Square edge 3 Prime layer 4 Face 5 Elementary reinforcement 6 Back Figure 1 - Cutaway drawing of a unit with square edges, reinforced with organic fibre (jute or sisal fibre)
Key 1 Thickness 2 Bevelled edge 3 Face
4 Elementary reinforcement 5 Back Figure 2 - Cutaway drawing of a unit with bevelled edges, reinforced with chopped glass fibre roving

Key 1 Reinforcement rim edge
6 Back 2 Rebate for surface jointing
7 Fibrous plaster rope 3 Prime layer
8 Complementary reinforcement 4 Face
9 Elementary reinforcement 5 Thickness Figure 3 - Cutaway drawing of a unit with rebated edges for surface jointing, reinforced with glass fibre tissue and complementary reinforcement by softwood laths 4 Classifications 4.1 Categories of production There are three categories of production of fibrous gypsum plaster products defined by their manufacturing process and commercial destination (see annex D): a) "cpp" Conventional series production Concerns products placed on the market, manufactured in large volumes of the same product made over time. b) "cppv" Series production of products with varying properties Concerns products placed on the market, manufactured in series production with different performances (e.g. different size, shape, strength). c) "ipp" Individual (and non-series) production (see scope),
Concerns products of individual design that are ordered for and installed in one and the same known work. Under these conditions, "ipp" are : - individually designed and manufactured, upon request and for specific purposes ; or - custom-made for a specific order to obtain one or several end use performances different from products manufactured in series.
4.2 Product ranges There are three ranges of fibrous gypsum plaster casts, defined by their principal functions, shapes and
configurations : a) casts for interior architecture (see 3.1.2) b) casts for technical function (see 3.1.3) c) units (see 3.1.4)

NOTE Fire resistance is the property of an assembled system, not of the product itself. Where the manufacturer wishes to declare the characteristic (e.g. when it is subject to regulatory requirements), the performances of a relevant system composed of fibrous gypsum plaster casts shall be determined and classified according to EN 13501-2. 5.2 Dangerous substances Materials used in products shall not release any dangerous substances in excess of the maximum permitted levels specified in a relevant European Standard for the material or permitted in the national regulations of the member state of destination. 5.3 Impact resistance
NOTE Impact resistance is a characteristic dependent on an assembled system and not of the product in isolation. Where the manufacturer wishes to declare the characteristic (e.g. when it is subject to regulatory requirements), the impact resistance of a system composed of fibrous gypsum plaster casts shall be determined according to ISO 7892. 5.4 Protection against noise
NOTE Airborne sound insulation is a characteristic dependent on an assembled system and not of the product in isolation. 5.4.1 Airborne sound insulation 5.4.1.1 Direct airborne sound insulation Where the manufacturer wishes to declare the characteristic (e.g. when it is subject to regulatory requirements), the direct airborne sound insulation performance of a suitable system composed of fibrous gypsum plaster casts shall be determined according to EN ISO 140-3, with the sound rating (R) being determined according to EN ISO 717-1. 5.4.1.2 Insulation of a suspended ceiling with a plenum above it Where the manufacturer wishes to declare the characteristic (e.g. when it is subject to regulatory requirements), the airborne sound insulation performance of a suitable system composed of fibrous gypsum plaster casts shall be determined according to EN 20140-9, with the sound rating (Dn,c) being determined according to EN ISO 717-1. 5.4.2 Acoustic absorption NOTE Acoustic absorption is a characteristic dependent on an assembled system and not of the product in isolation.

5.6.2 Water The mixing water shall be clean and free from contamination Normal tap water may be used.
5.6.3 Reinforcements The reinforcement shall generally comprise one or more (e.g. elementary reinforcement of hessian with complementary reinforcement made of lightweight steel sections) of the types defined in 5.6.3.1, 5.6.3.2. 5.6.3.3. The reinforcements are classified according to their characteristics and their use, as described in Table 2. 5.6.3.1 Organic reinforcements 5.6.3.1.1 Jute and sisal fibres Organic fibres consisting of jute (for example, Corchorus olitorius or Corchorus apsularis) and sisal (for example, Agave sisalana perrine) shall be in the form of new natural fibres, comprising long strands which are sound, combed or carded and free from impurities and foreign bodies. 5.6.3.1.2 Hessian (or woven jute fibre) Jute cloth (Corchorus olitorius or Corchorus apsularis) or mix of hemp and jute cloth, shall be regular, plain, uniform and with no visible defects. The nominal weight of common woven jute fibre is equal to 92 g/m², 96 g/m² or 125 g/m². The structure of the weave shall permit bonding of two layers of the moulding plaster; the usual openings in the weave are between 4 mm and 10 mm.

The cross-sections normally used are: 25 mm x 3 mm, 25 mm x 6 mm, 24 mm x 9 mm, 27 mm x 7 mm.
5.6.3.2 Mineral reinforcements 5.6.3.2.1 Chopped glass fibres Common glass fibres used are following types:  non-twisted chopped glass fibre silionne EC, coated with a water soluble sizing agent; the lengths may be between 13 mm and 50 mm ;  non-twisted multi-fibre glass roving (called Stratifil EC) ; these may be chopped when installed. 5.6.3.2.2 Glass fibre tissue Glass fibre tissue shall comprise glass fibre silionne, coated with a water-soluble sizing agent. The structure of the tissue shall permit bonding of two layers of the moulding gypsum plaster.
5.6.3.2.3 Glass fibre mat Glass fibre mat shall comprise glass fibres silionne or verrane in multiple layers of random distribution and adhered with a binder. Their structure shall permit bonding of the two layers of moulding gypsum plaster. 5.6.3.3 Metal reinforcements 5.6.3.3.1 Metal mesh and cloth These consist of mild steel wire, assembled to form a mesh and protected against corrosion. This protection is ensured by hot-dip galvanizing as specified in EN 10244-2. Cotton scrim wrapped around galvanised mild steel wire may also be used. A different method shall be used as long as it offers at least an equivalent degree of protection.
5.6.3.3.2 Metal lath Expanded lath, ribbed lath and welded mesh lath shall conform to EN 13658-1.
Welded mesh lath shall be used without cardboard backing. 5.6.3.3.3 Lightweight steel sections Lightweight steel sections of various profiles and sizes may be used to provide complementary reinforcement. Steel sections shall be manufactured from mild steel strip having a protective coating in compliance with EN 10327. The protective coating shall comply with one of the following classes indicated in Table 1.

Table 1 — Protective coating classes All classes Z
EN 10327 Class ZA130 EN 10327 Class ZA095 EN 10327 Class AZ 150 EN 10327 Class AZ 100 EN 10327 NOTE Z means zinc, ZA zinc/aluminium, AZ aluminium/zinc,. Number is the total weight of coating in g/m 2.
A different method may be used as long as it offers at least an equivalent degree of protection.

Casts with only elementary reinforcement Casts with elementary and complementary reinforcement
Softwood lath (w) Lightweight steel sections (m) Configuration Origin Designation Reference clauses
5.6.3.1.3 5.6.3.3.3
Organic Jute and sisal fibre 5.6.3.1.1
f1 f1w f1m Random Mineral Chopped glass fibres 5.6.3.2.1
f2 f2w f2m
Organic Hessian 5.6.3.1.2
f3 f3w f3m
Glass fibre tissue 5.6.3.2.2
Sheet Mineral Glass fibre mat 5.6.3.2.3 f4 f4w f4m
Metal mesh and cloth 5.6.3.3.1
Metal Metal lath 5.6.3.3.2 f5
f5m NOTE 1 Common classes of reinforcement are shown in bold type. NOTE 2 Other possible reinforcement classes may be expressed by analogy (e.g. : elementary reinforcement by glass fibre mat and complementary reinforcement by softwood lath and lightweight steel sections = f4 wm).

Key
1 Wads 2 Handling framework Figure 4 - Handling framework
Key 1 Nominal thickness 2 Prime layer 3 Thinner thicknesses 4 Back 5 Face 6 Reinforced plaster Figure 5 - Thinner thicknesses at the bottom recessed points of relief of a cast

 streaks;  mould bubbles (small balls of plaster);  cavities;  lack of plaster on details;  spalls and chips on sharp edges.
Tolerances : Any three of the following small defects are allowed per m² of the developed area:  individual streaks less than 500 mm long;  mould bubbles;  cavities or lack of plaster, when they can be circumscribed within a 3 mm edge square;  spalls and chips on sharp edges.
Inspection of the face shall be carried out in accordance with 6.3. 5.7.2 Back The back of the fibrous gypsum plaster casts may be smooth or rough depending on the installation system. NOTE Where there is a handling framework, it is generally fixed to the back by wads or fibrous gypsum plaster ropes.
5.7.3 Edges The edges of the fibrous gypsum plaster casts shall be free from spalls, chips and other imperfections.
They are permissible when the edges are intended to be sealed and pointed. Inspection of the edges shall be carried out in accordance with 6.3

A cut on a fibrous gypsum plaster cast shall have a continuous texture with no separation between the layers of plaster. Inspection of a cut shall be carried out upon thickness checking 6.4 and 6.12 NOTE Casts for technical functions intended to be concealed in the completed works (eg. Shaft in suspended ceiling), are not concerned by 5.7.1 (except fissures) and 5.7.3. 5.8 Thickness of the prime layer (fibrous plaster firstings) Normally, the thickness of the prime layer of the fibrous gypsum plaster casts shall not be less than the recommended dimensions stated in Table 3, defined by their reinforcement classes. NOTE Casts reinforced with reinforcements class f2, f2w, f2m, do not include prime layer. The thickness of the prime layer shall be measured in accordance with 6.4. Lower thickness is allowed at recessed points of relief (see figure 5). Table 3 — Recommended minimum thickness of the prime layer of fibrous gypsum plaster cast Product Reinforcement classes Minimum thickness of the prime layer of the cast
mm
Traditional fibrous gypsum plaster f1, f1w, f1m f3, f3w, f3m f4, f4w, f4m
f5, f5m 5 GRG and PMGRG
f4, f4w, f4m 1 5.9 Handling framework
The fibrous gypsum plaster casts can be reinforced by a framework of wood or metal (see 3.2.12 and figure 4). To avoid corrosion during the drying period and setting, the steel sections in contact with fibrous gypsum plaster casts shall be protected by hot galvanising or by paint (single layer). 5.10 Resistance to impact by a hard steel ball and cohesion When tested in accordance with 6.5, the steel ball shall not pass through the cast. 5.11 Moisture content The moisture content specifications apply only to wrapped fibrous gypsum plaster casts of the "cpp" category. When tested in accordance with 6.6, the moisture content Mc measured at the time of departure from the workshop shall not exceed the following values for products intended to be wrapped:  a) with airtight wrapping (e.g. polyethylene) :Mc ≤ 4 % ;

Table 4 — Minimum thicknesses of the interior architectural and technical function casts Dimensions and tolerances in millimetres Product Reinforcement classes Minimum thickness Tolerance at recessed points of relief (see Figure 5 and 6.9.4)
Interior architectural casts out of reach Other architectural casts and technical function casts
Low deviation
High deviation
Traditional
f1w, f1m f3w, f3m f4w, f4m
- 1 fibrous gypsum plaster f1 f2w, f2m f3 f4
-2
Depending on the shapes and use of the casts, overthicknesses are permitted
f2 10 10
f5, f5m 15 15
GRG and PMGRG f2w, f2m f4w, f4m 3 5
- 1
f2, f4 5 5
5.15 Units - Additional requirements
In addition to the specifications described in 5.1 to 5.13, fibrous gypsum plaster units shall meet the following requirements:
5.15.1 Dimensions of units and tolerances The unit dimensions shall be defined by the length, the width and the thickness. 5.15.1.1 Length and width The length shall be measured in accordance with 6.10 and the width shall be measured in accordance with 6.11. NOTE The current nominal lengths are between 1000 mm and 2000 mm inclusive
The current nominal widths are between 800 mm and 1000 mm inclusive The tolerances on the nominal dimensions – length and width – declared by the manufacturer are as follows: a) for traditional fibrous gypsum plaster units: ± 5 mm ; b) for GRG or PMGRG units:

The tolerance for the thickness declared by the producer shall be + 2 mm /- 1 mm.
NOTE The current nominal thicknesses are 5 mm, 10 mm, 12 mm, 15 mm, 20 mm for traditional fibrous gypsum plaster and 3 mm and 9 mm for GRG and PMGRG. Table 5 — Minimum thickness of units Product Reinforcement classes Minimum thickness
mm
f1w, f1m, f3w, f3m, f4w, f4m 5 Traditional fibrous gypsum plaster f1, f2, f2w, f2m, f3, f4 10
f5, f5m 15 GRG and PMGRG
f2w, f2m, f4w, f4m 3
f2, f4 5 5.15.2 Squareness of units and tolerances The angles of the units shall be square.
When measured in accordance with 6.13, deviations shall not be greater than:
a) 2 mm for traditional fibrous gypsum plaster; b) 0,6 mm for GRG and PMGRG. 5.15.3 Flatness of the face of units and tolerances The face of the unit shall be flat. 5.15.3.1 General flatness When the test is carried out in the manufacturing plant, the general flatness of the face shall be measured on the mould base in accordance with 6.14.1. NOTE The flexibility of the material and the possible presence of complementary reinforcement makes the testing of this requirement on the unit difficult. Any deviation from general flatness shall not be greater than 1 mm in 1000 mm 5.15.3.2 Local flatness When measured on the face in accordance with 6.14.2, any deviation from flatness for local areas shall not be greater than 0,6 mm in 300 mm.

When tested as described in 6.15, the surface mass of traditional fibrous gypsum plaster units shall be at least of the following values :
a) 1 kg/m2 per mm of thickness for units incorporating f1 or f3 reinforcement; b) 0,9 kg/m2 per mm of thickness for units incorporating f2 or f4 reinforcement. NOTE This requirement is not applicable to units with reinforcements of classes f5 and f5m, nor to those containing aggregates. For GRG and PMGRG units, the surface mass shall be at least 1,4 kg/m² per mm of thickness when tested as described in 6.15. When determined in accordance with 6.15, the tolerance on the mass declared by the producer shall be :
+ 10 % /- 5 %
6 Test methods 6.1 Sampling The following procedure shall be adopted: A minimum of three samples of each type are required to carry out the physical, chemical and mechanical tests (6.3 to 6.15).
Annex A provides a sampling procedure. 6.2 Conditioning of samples Samples shall be conditioned as follows : Weigh the selected samples (mass M1) and then dry them to constant mass (mass M2). They are then subjected to the different tests specified in this standard. NOTE 1 Constant mass is attained when two successive weighings differ by less than 0,2 % in 24 h. Drying to constant mass is carried out using one of the two following methods:
a) method A: storage in a ventilated room at 23 °C ± 2 °C and 50 % ± 5 % relative humidity ; b) method B: storage in a drying cabinet at 40 °C ± 2 °C prior to cooling to room temperature. NOTE 2 Constant mass is only necessary for tests 6.3.4 2.b), 6.5, 6.6, 6.7, 6.8, 6.14.2 and 6.15 6.3 Checking of the moulding definition of the face 6.3.1 Principle Visual inspection of the cast and measurement of defects shall be carried out as follows. 6.3.2 Apparatus
Metal rule or metal tape graduated in millimetres. Gauge made from a thin metal or plastic plate containing a 3 mm x 3 mm square hole.

6.3.4.2 Method of calculation of developed area The developed area of the face of interior architectural and technical function casts, is calculated using one of the two following methods: a) for casts with a simple configuration: measurement, calculation and adding up of elementary areas; NOTE Example: expansion of a cornice with a dressmaker's tape measure.
b) for casts with a complex configuration: calculation of conventional areas, given by the formula : ()5432MMMMAd+−= where Ad
is the developed area, in m²; M2
is the mass of the cast dried to constant mass, in kg; M3
is the mass of any metal reinforcements (class: f5), in kg; M4
is the mass of any handling frameworks, in kg; M5
is the theoretical surface mass of the cast calculated as a function of its nominal thickness and one of the three minimum surface masses given in 5.15.4.
For these casts with a complex configuration, a simplified calculation of the developed area is permitted.
6.3.5 Expression of results To notice visible defects to the naked eye, divide the number of defects by the developed area.
...