Finishes

Alan Everett, Yvonne Dean

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781317890058
• Edition: 4
• Topic: Architektur
• Subtopic: Architektur Allgemein

The fourth edition of this well established text brings the subject up-to-date with environmental legislation and provides a thorough understanding of the surface technologies of all materials used for finishes. It also aims to minimise the use of finishes which have shorter lives and hence need renewing more frequently. As the variety of materials used for finishes is so large, they have been grouped into their engineering categories of ceramics, polymers, metals and composites to aid understanding of their structure, behaviour and ability to resist degradation. Finishes is an essential textbook for Materials units on building, architecture, surveying and related degree and postgraduate courses, and for students of BTEC HNC/D building and surveying.

1
Introduction

Although this volume is concerned with ‘Finishes’ as a subject, a title such as ‘The Visible Appearance of the Building Fabric % or even ‘The External Skin and its Behavioural Properties and Characteristics’ might be more appropriate. The use of finishes is often regarded as a separate and final application to the fabric of the building, sometimes even the last part of the building to be specified. This may mean finishes are subject to compromise in their quality by late cost-control exercises. However, finishes represent the true boundary of a building, the face for immediate contact and, more critically, should be seen as the first line of defence for protection of the fundamental fabric of the building. Some finishing elements are a good deal more substantial than others and are often part of the solid external skin, and distinct from further applied coverings or coatings. Consequently finishes are one area of the building industry that is continually involved in replacing materials in a way that could be seen as sacrificial.

Figure 1.1 Peuterey Ridge and Aiguille Noir, Mont Blanc, September 1981. The scale of exposure that our buildings have to cope with is easily forgotten, and our climatic extremes are often peaks in an undulating chart of annual variations. If we catered for the worst possible conditions, our buildings would be better equipped for survival. (Photograph: Steve Keates.)

It is still appropriate and convenient to think of thick and thin finishes or, to be more exact, macro and micro finishes. Micro finishes refer to paints, films, and other surface finishes whose substance and thickness is difficult or impossible to determine or measure accurately with the naked eye. The basic unit used is 10^-6 m and is referred to as a ‘micron’. Macro finishes are large-scale materials that can be seen with the naked eye. A reasonable estimate can be given of their chief characteristics and dimensions, which will be in millimetres and metres. Macro finishes still have a detailed microstructure that determines their properties and behaviour.

Both categories of finish are used externally and internally and there are different environments for both categories. In fact, the range of temperatures and conditions in which we expect materials not only to survive, but also to remain stable, is extraordinary. Even in the British Isles, human beings cannot survive for long at the extremes of these basic parameters if totally exposed.

We also rely to a great extent on our own observational experience to judge conditions and to make an appropriate choice of materials, but our individual views as designers, architects, contractors and practitioners are limited.

The internal movements of molten magma in the upper mantle, together with the shifting of tectonic plates, contribute to distort the thin outer skin of the Earth’s continental and oceanic crust into mountains, volcanoes and other features. The Earth, under the continual action of rain and wind-borne dust, would become smooth and polished like a well worn pebble on a beach, were it not for this internal disruption that continually changes the profile of its surface.

The fabric of our buildings is also exposed continually to a cyclical action of wind, rain, cold and heat which in the long term erodes naturally all physical features on Earth. Chemistry too can erode an outer surface by encouraging the deterioration of materials.

Deterioration, however, is an inaccurate description of this process: materials alter to become chemically stable in our atmosphere. This is usually a state described in thermodynamics as one of ‘low free energy’. Complex man-made products usually have sophisticated structures, and their very existence depends on a too-easily altered energy balance.

In this century many finishes have been affected by higher levels of pollution and there has been great concern with the effect of acid rain. Emissions of acid into the atmosphere seemed to peak in 1970 and there has now been a reduction of almost 30% in the acidity of some lakes. De-sulphurisation of waste gases from power stations has reduced emissions of sulphur dioxide and the British Govt did agree with the EC to cuts totalling some 60% by 1993. The fall out of nitric acid is now more significant as a contributor to acid rain than sulphur dioxide. The most evident indicator of this type of pollution is ‘sick tree syndrome’ where the needles of conifers change colour and die. However, this type of tree sickness may also be attributable to the effects of magnesium deficiency from the long hot dry summers of the early 80s. Lack of rain effected the release of this mineral from the forest floor into the earth and it stunted root growth. The accumulation of acids, sulphate and nitrates in the soil since the industrial revolution has certainly also affected root growth.¹

As building professionals, we use a technology that is generally inappropriate to deal with the very real and large-scale events that are commonplace in our environment and we construct without consideration for the effects of weather, climatic change, sunshine or temperature. Physics, earth sciences and chemistry have become so remote and so specialized that the experience gained in these fields is usually not easily transferable and therefore not often used in the low technology field of building. We also use high technology solutions to help us out of awkward situations where our building technology is inadequate. In fact we are really seeking solutions that are sophisticated in terms of their complexity, and yet are an abuse of some fundamental principles in science. This can hasten decay in buildings and also use up primary resources, not only in terms of the raw materials extracted and refined for construction and repair, but also in terms of energy used in their processing and treatment to keep them in a stable state.

Environmental legislation

In the last decade our general concern with the effects of manufacturing industries and consequential environmental impact has been followed by global, European and national agreements.² The first United Nations Conferences on the Environment and Development resulted in the Rio Declaration to assist environmental action and future development. Agenda 21 set out a plan of action for the 21st century which emphasizes the need for energy-efficient technologies, renewable energy sources and the reduction of pollution levels.³ Policy is fast being supplemented by action that satisfies public concern. Legislation is becoming increasingly difficult to keep up with and many new directives are now being issued through the EC. Individuals want to show they are complying with new directives even though enforcement is minimal. Dissemination of new material through the technical press is slow and the best sources for environmental information are a network of European Documentation Centres in Britain. These include the main Science and Technical reference library of the British Library in Holbom, selected Universities and major Chambers of Commerce. There is the Manual of Environmental Policy: the EC and Britain which is updated twice a year. This includes all the latest EC environmental directives with commentaries on their development and effect.

1.1 The importance of specification

The correct specification of finishes is vital to the durability and appropriate use of a given material.

Most finishes applied to the surface of buildings fall into two major categories: polymers and ceramics. If the nature of these materials is understood then their correct application and use will be easier to specify. Consequently this book groups finishes into categories with similar characteristics as normally defined in materials science. It is unreasonable to suppose that designers can memorize the properties of different products individually. A general understanding of polymeric materials and how they behave will assist in the specification and use of finishes such as paint, flooring compounds, roofing compounds and adhesives. Similarly, an understanding of the properties of ceramic materials and how they fail helps in determining their use in the design of fixings and in carefully supervising during installation.

In the past textbooks on this subject tended to be reference books. They dealt with the history, practice and usage of materials and their finishes. These books, usually a three or four volume set, encompassed the state of the art in building. They were also prescriptive, i.e. they were able to detail the exact materials in use at the time with their limited and proven application.

In the latter part of the twentieth century we have seen a great increase in the materials and products available. Descriptions of all these products can be obtained from publications produced and updated annually by the Architectural Press, Barbour Microfile, RIBA Publications Ltd and, more recently, the Building Technical File. These are core sources and should always be used as the starting point for investigation. The Building Centre can be used for queries on products and the Building Research Establishment for advice and diagnosis on building failures. The Design Centre offers advice on innovation in materials technology at its new Materials Centre. To ensure that there are no omissions in a specification, the National Building Specification now requires a standard list of documentation.

A textbook today can provide a broad background of the scientific principles. Armed with an understanding of materials and the mechanics of their deterioration, a diagnostic attitude to the use of materials can be developed by the student. This should lead to a greater sensitivity in the specification of finishes and their uses.

1.2 A strategy for specification

At some point every designer, architect or contractor deals with the specification of materials. Architects and designers have very specific responsibilities under the terms of their contractual arrangements with clients. These are further reinforced in standard building contracts. This responsibility cannot be delegated without agreement and designers must remain in control of the situation. It is the contractors’ or subcontractors’ responsibility to carry out the works as specified. Clauses of contracts in current use should be very carefully checked.

Far too often a document is written using information compiled for a different project. This information is repeated without checking it at source. Or information such as numbers for British Standards is copied without confirming its relevant or validity, or even whether a BS number is still available and not superseded. Instead of attempting to find a master document to imitate, it is far more useful to develop a clear strategy about specifying materials and to apply a simple set of parameters to each material or component in order to build up a reservoir of information. Existing specifications can then be used as checklists but care should always be taken. No specification will be sufficiently exhaustive to deal with every aspect of a particular building. The quotation of a British Standard may on the other hand be too broad for a specific requirement. Even the National Building Specification may still need clarification of particular items. If the following three steps are taken for every component in a building, a reasonable specification can be compiled:

1. The nature and composition of a material or component should be specified by reference to available and current British or other recognized standards and/or Agrément Certificates, and in conjunction with manufacturers’ literature if applicable.
2. The method of fixing or placing these materials in position should be specified and the use of codes of practice and their relevant parts clearly outlined.
3. The method of protection or finish to the materials should be stated and specified together with their fixings. This may reveal that fixings should not have an applied finish but the nature of their fixings needs more careful specification.

The specifier must be organized: as the design or decision is made, information is kept perhaps in a loose-leaf binder or on a disc on a computer. The information should be concise and simply stated. There is no need to be legalistic, just be precise and clear about everything to be used. If this is done systematically you will have a good specification document and the source of information for Bills of Quantities. Errors and consequent failures in building are often associated with poor specification. Often the process of specifying materials is the last activity in the design process. In order to expedite documentation at the end of a project, fast decision-making may ultimately commit the designer and the contractor to unsound detailing and predictable repercussions. A good specification is inseparable from the intentions of the original designer backed up by technologically sound information.

1.3 How to use this book

This book is designed to be more than a reference volume. When considering a particular finishing material, it should first of all be identified as either a polymeric, ceramic, metallic or composite material. The general introduction in the relevant section provides the basic principles about the behaviour of the material. Reference can then be made to applications of individual materials. There are overlaps between these areas.

When using this book as a basic text all the introductory sections should be read first to give a broad base for understanding the subject. The glossary sections are expansive explanations of terms used in the relevant sections and should be treated as an informative dictionary.

For those with particular needs on the precise specification of materials, direction is given to source material such as British Standards and other specification documents.

Standards are often quoted by number without being scrutinized first by the specifier. If they were, practitioners would possibly find that the very clear directives and advice given in these documents conflicts with their own clauses and choice of specification.

Often the names and numbers of particular standards are quoted in their entirety by practioners when only a small section is relevant.

Up to date British Standards and Codes of Practice should be available for constant reference. It is confusing to quote to contractors entire standards when it is unnecessary and it is more likely that the guidance given will be ignored. The misuse of reference material also implies a lack of knowledge of the terms of the standard on the part of the specifier.

Moreover the reference to a British Standard does not absolve the specifier from legal responsibilities. A phrase often quoted in British Standards is:

‘Compliance with a British Standard does not of itself confer immunity from legal obligations.’

Photographs

All the photographs have been selected to illustrate particular points. Some photos have a ‘dot’ which measures 8 mm in diameter and conveys an idea of scale.

Notes

1 New Scientist 15th September 1990.

2 The E...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Acknowledgements
• 1 Introduction
• 2 Polymeric materials
• 3 Applications of polymeric materials
• 4 Ceramic materials
• 5 Applications of ceramic materials
• 6 Metals
• 7 Composites
• 8 Conclusion
• Index