bs 4756
DESCRIPTION
BS 4756TRANSCRIPT
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BRITISH STANDARD BS 4756:1998
ICS 87.040
NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW
Specification for
Ready-mixed aluminiumpriming paints forwoodwork
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This British Standard, havingbeen prepared under thedirection of the Sector Board forMaterials and Chemicals, waspublished under the authority ofthe Standards Board and comesinto effect on15 July 1998
BSI 1998
First published August 1971Second edition July 1998
The following BSI referencesrelate to the work on thisstandard:Committee reference STI/28Draft for comment 97/122321 DC
ISBN 0 580 29565 6
BS 4756:1998
Amendments issued since publication
Amd. No. Date Text affected
Committees responsible for thisBritish Standard
The preparation of this British Standard was entrusted to Technical CommitteeSTI/28, Paint systems for non-metallic substrates, upon which the following bodieswere represented:
British Cement Association
British Coatings Federation Ltd.
British Decorators' Association
Department for Education
Department of the Environment, Transport and the Regions (represented by the
Building Research Establishment)
Department of the Environment, Transport and the Regions (Construction
Sponsorship Directorate)
European Resin Manufacturers' Association
Furniture Industry Research Association
Oil and Colour Chemists' Association
Society of Chemical Industry
Timber Research and Development Association
Union of Construction, Allied Trades and Technicians
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BS 4756:1998
BSI 1998 i
Contents
Page
Committees responsible Inside front cover
Foreword ii
Specification
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Composition 1
5 Sample 1
6 Reference sample 2
7 Consistency 2
8 Drying time 2
9 Flexibility and adhesion 2
10 Application properties and finish 2
11 Keeping properties 2
12 Marking 2
Annex A (normative) Method of test for drying time over both untreated andpreservative-treated wood 3
Table 1 Ð Composition 1
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ii BSI 1998
BS 4756:1998
Foreword
This British Standard has been prepared by Technical Committee STI/28. It supersedesBS 4756:1971, which is withdrawn. It incorporates certain specific requirements ofDefence Specification DEF 1418.
Paints conforming to this British Standard are designed for application by brush toexterior or interior wood.
It is generally recommended that where paints conforming to this British Standard areapplied to exterior wood, they are overcoated as soon as is practical. It has been foundthat if they are allowed to weather, the adhesion of subsequent coats of paints can beadversely affected.
The paints as specified are ready for use and additional thinners should not be added.
Depending on whether leafing or non-leafing aluminium pigment is used, the paintsmay produce a bright or dull aluminium finish.
A British Standard does not purport to include all the necessary provisions of acontract. Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunityfrom legal obligations.
Summary of pages
This document comprises a front cover, an inside front cover, pages i and ii, pages 1to 3 and a back cover.
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BSI 1998 1
BS 4756:1998
Specification
1 ScopeThis British Standard specifies two types ofready-mixed aluminium priming paint for brushapplication to woodwork, as follows.
a) Type 1. Not recommended for woods treatedwith metallic naphthenate preservatives, nor wheremaximum resistance is required.
b) Type 2. Recommended where the type 1material is not suitable, and particularly suitablefor the painting of naturally resinous woods ortimber which may exude resin-like matter arisingfrom treatment with copper naphthenate or similarwood preserving solutions.
Neither type is suitable for use over timberpreserved with tar-oil products.
2 Normative referencesThe following normative documents containprovisions which, through reference in this text,constitute provisions of this British Standard. Fordated references, subsequent amendments to, orrevisions of, any of these publications do not apply.For undated references, the latest edition of thepublication referred to applies.
BS 388:1972, Specification for aluminium pigments.
BS 391:1987, Specification for tung oil in paints andvarnishes.
BS 2015:1992, Glossary of paint and related terms.
BS 4725:1987, Specification for linseed stand oil forpaints and varnishes.
BS 5707:1997, Specification for preparations of woodpreservatives in organic solvents.
BS 6900:1987, Specification for raw, refined andboiled linseed oils for paints and varnishes.
BS 7664:1993, Specification for undercoat andfinishing paints.
BS EN 971-1:1996, Paints and varnishes Ð Termsand definitions for coating materials Ð Part 1:General terms.
BS EN 21512:1994, Methods of test for paints ÐSampling.
BS EN ISO 1513:1995, Paints and varnishes ÐExamination and preparation of samples fortesting.
BS EN ISO 1514:1997, Paints and varnishes ÐStandard panels for testing.
BS EN ISO 1519:1995, Paints and varnishes Ð Bendtest (cylindrical mandrel).
ISO 554:1976, Standard atmospheres forconditioning and/or testing Ð Specifications.
3 Terms and definitionsFor the purposes of this British Standard, the termsand definitions given in BS 2015 and BS EN 971-1apply.
4 Composition
4.1 General
The general composition of the paints shall be asgiven in Table 1.
Table 1 Ð Composition
Constituent Percentage by mass
Type 1 Type 2
Non-leafing orleafing aluminiumpaste conformingto BS 388
13, minimum(as metal)
18.5, minimum(as metal)
Binder (see 4.2) 33, minimum 33, minimum
Thinners, driers Remainder Remainder
4.2 Binder
4.2.1 Type 1
For type 1 paints, the binder shall consist of either ofthe following.
a) An alkyd resin containing not less than 55 % bymass of drying oil fatty acids. The addition of notmore than 15 % by mass of an oleoresinous varnishof oil-to-resin ratio not less than 2:1 is permitted.
b) A varnish containing unmodified alkyl phenolresin with a mixture of refined linseed oil and tungoil, conforming to BS 6900 and BS 391respectively, giving an oil-to-resin ratio of not lessthan 3:1. The ratio of tung oil to linseed oil shallnot be less than 1:2.
4.2.2 Type 2
For type 2 paints, the binder shall consist of avarnish containing unmodified alkyl phenol resinwith a mixture of light linseed stand oil and tung oil,conforming to BS 4725 and BS 391 respectively,giving an oil-to-resin ratio of not less than 4:1. Theratio of tung oil to linseed stand oil shall not be lessthan 9:1.
5 SampleFor assessing conformity to the requirements ofclauses 7 to 11, representative samples of thematerial, of not less than 250 ml, shall be taken andpacked in the manner described in BS EN 21512.
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2 BSI 1998
BS 4756:1998
1) Marking BS 4756:1998 on or in relation to a product represents a manufacturer's declaration of conformity, i.e. a claim by or on behalfof the manufacturer that the product meets the requirements of the standard. The accuracy of the claim is solely the claimant'sresponsibility. Such a declaration is not to be confused with third-party certification of conformity, which may also be desirable.
6 Reference sampleBy test and agreement, a sample shall be accepted asmeeting all the requirements of clauses 4 and 7 to 11,and shall be the reference sample. The sample shallnot be less than 250 ml and shall be packed in themanner described in BS EN ISO 1513.
7 ConsistencyThe material shall be in such a condition that stirringeasily produces a smooth, uniform mixture, suitablefor application by brushing.
8 Drying timeWhen tested in the manner described in annex A, thematerial shall become dry for recoating in not morethan 24 h and the appearance of the undercoatedpanel shall be similar to that of a panel preparedfrom the reference sample, when tested in a similarway.
9 Flexibility and adhesionWhen applied to a 0.3 mm thick panel of burnishedsoft aluminium, prepared as described inBS EN ISO 1514 to give a dried mass of 20 g/m2
to 30 g/m2 and tested as described inBS EN ISO 1519, using the type 1 apparatus witha 6 mm mandrel, the material shall not showcracking or loss of adhesion.
10 Application properties and finishWhen allowed to dry for 24 h at a temperature of(20 ± 2) 8C and a relative humidity of (65 ± 5) % inaccordance with ISO 554, a test panel prepared asdescribed in annex A shall have a smooth aluminiumfinish, free from sagging and wrinkling. Theappearance of the test panel shall be similar to thatof a test panel prepared using the reference sample.
11 Keeping propertiesThe material, when stored at normal roomtemperature in its original sealed containers, shallretain the properties detailed in clauses 7 to 10 for aperiod of not less than 12 months from the date ofdispatch to the purchaser. The material shall showno evidence of gassing when stored over the sameperiod.
12 MarkingEach container shall be clearly marked with thefollowing information:
a) the manufacturer's name, trade mark andproduct designation;
b) the method of application;
c) the recommended spreading rate, expressed insquare metres per litre;
d) the number and date of this British Standard,i.e. BS 4756:19981);
e) the batch number and/or date of manufacture.
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BS 4756:1998
BSI 1998 3
Annex A (normative)
Method of test for drying time over bothuntreated and preservative-treated wood
A.1 Preparation of test panels
A.1.1 Wood
The panels shall be made from straight-grainedEuropean redwood or home-grown Scots pine ofnormal growth rate (3 to 8 annual growth ringsper 10 mm), free from knots, shakes, resinous streaks,visible blue fungal infection and abnormal porosity dueto bacterial attack during storage. The inclination ofthe growth rings shall be 08 to 458.NOTE Abnormal porosity can be detected qualitatively by therapid absorption of a drop of propan-2-ol applied to a smoothsurface. The drop is not absorbed in less than 30 s by wood ofnormal porosity.
The wood shall be conditioned at a temperature of(20 ± 2) 8C and a relative humidity of (65 ± 5) % inaccordance with ISO 554, until the moisture content ofthe wood has reached equilibrium. Any wood showingsurface splitting at this stage shall be rejected.
A.1.2 Panels
The panels shall be cut from sawn boards planed allround to approximately 375 mm3 100 mm3 20 mm,then machined to a smooth uniform finish. In order toachieve a clean finish to the end grain and to eliminateany tearing of fibres arising during cross-cutting, thefollowing procedure shall be used.
a) Flat-cut and thickness the wood toapproximately 2 mm above the final thickness.
b) Cross-cut the wood using a well sharpened anddressed tungsten carbide tipped circular saw.
c) Carry out final surfacing of the test face on anoverhand planer.
d) Do not carry out further preparation,e.g. smoothing with abrasive paper or cloth.
A.1.3 Selection
Select the panels carefully to give a sapwood testsurface on the convex side of the growth rings, withany heartwood confined to a band not exceeding 5 mmwhen measured from the rear face.
If the presence of heartwood in selected timber cannotbe detected by a difference in colour in the wood(heartwood is darker), it shall be checked by the brushapplication of a test solution to both the end grain andthe faces of a small piece cut from the same length ofwood.
Prepare a test solution by dissolving Fast Red B salt indeionized water at a concentration of 5 g/l. Use thefreshly prepared solution immediately. Heartwood isindicated by the development of a deep red colour,which usually shows within approximately 10 min.
WARNING. Fast Red B salt has no reported mutagenicor teratogenic effects; however, it should be treated asa suspected carcinogen. Reference should be made tothe relevant health and safety data sheets.
A.2 Procedure
A.2.1 General
One test panel is required for priming paint conformingto the compositional requirements (see clause 4) oftype 1, and two test panels for type 2, one of whichshall be treated with preservative in accordancewith A.2.2 before application of the priming paint.
A.2.2 Painting
Apply the priming paint to each panel to give a driedfilm mass of 20 g/m2 to 30 g/m2. Expose the panels todry in a vertical position, at a temperature of(20 ± 2) 8C and a relative humidity of (65 ± 5) %, inaccordance with ISO 554, for 24 h; then apply a coat ofwhite undercoat, conforming to BS 7664, by brush, tothe dried film. Examine each panel for signs ofdisturbance of the dried film. The priming film is dryfor recoating if the coat of undercoat can be appliedsatisfactorily . Re-examine the undercoated panels afterthey have been allowed to dry vertically for 24 h at atemperature of (20 ± 2) 8C and a relative humidityof (65 ± 5) %.
A.2.3 Preservative treatment (for type 2 only)
For priming paint conforming to the compositionalrequirements of type 2, treat the second test panel witha copper naphthenate preservative solution conformingto type F8 of BS 5707:1997, Table 1, prior to applicationof the primer. Immerse the panel for 3 min in thepreservative solution, and then allow it to dry with freeaccess of air for 24 h, at a temperature of (20 ± 2) 8Cand a relative humidity of (65 ± 5) % in accordancewith ISO 554.
If the test panel, whilst immersed in the preservativesolution, shows excessive escape of air, discard it asbeing too porous.
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