CERAMIC FLOOR AND WALL TILE: PERFORMANCE AND CONTROVERSIES CONTENTS CHAPTER 1 Quality and performance CHAPTER 2 Technical characteristics CHAPTER 3 Planning, design and installation of a tiled floor or wall CHAPTER 4 Defects leading to controversies Conclusions References CHAPTER 1 QUALITY AND PERFORMANCE -Introduction -Fabrication Technology and Product Types -Standards and Requisites -Choice Criteria CHAPTER 1 QUALITY AND PERFORMANCE INTRODUCTION There are two main reasons why floors and walls are usually covered with various materials. One hastodowithaestheticrequirements,toimprovetheappearanceandmakethefloororwall morepleasingtotheeye.Theotheristosatisfyfunctionalrequirements,toprotecttheflooror wallfrom aggressive action of the environment with a surface having suitable characteristics of impermeability, stability, durability and ease of cleaning.Variousmaterialsandtechniquescanbeusedtocoverfloorsandwalls.Wallscanbecovered with cement- or gypsum-based plaster, painted or papered, or covered with cloth or cork. Floors canbecoveredwithnaturalstonesuchasmarbleorgranite,withconglomeratecementbrick, wood, plastic (in the form of sheets or tile), carpet, etc.One of the more important, traditional materials widely used to cover floors and walls is ceramic tile.Ceramictileisaveryancientmaterial.Thefirstexamplesofitsusetocoveranddecorate surfaces date back to the Babylonian civilization, i.e., to the VI century B.C. Over the centuries, the fabrication technology and decorative potential of ceramic tile have been gradually amplified and perfected. For hundreds of years ceramic tile remained a luxury product, used for floors and walls in the homes of the wealthy. In this century, especially after World War II, the production of ceramic floor and wall tile underwent considerable industrial development with the advent of mass production techniques, especially in some countries such as Italy which had a long tradition intheuseofceramics.Theabilitytoproducetileonanindustrialscaleledtolowerprices making ceramic tile a product which could be afforded by the masses.In the initial phase of this period, ceramic tiles were used mainly to satisfy particular functional requirements for surfaces which were hygienic and easy to clean and thus were most often used for floors and walls in bathrooms and kitchens. The ceramic floor and wall tile industry, evolved rapidly,developingnewtypesofglazes,newfabricationtechnologiesandnewmaterials,to widenconsiderablytherangeandtypesofceramictileavailable.Asaresult,ceramictile graduallycametobeconsideredavalidmaterialforotherroomsinthehome,suchasliving rooms,entranceways,andbedroomsaswellasamaterialtobeusedinpublicandindustrial environments, both inside and out-of-doors. Thereasonsforthisconsiderablediffusion ofceramicfloorandwalltilecanbefound, on the one hand, in the wide range of colors, decorativepossibilitiesandshapeswhich allowthe designer and architect a variety of designsolutionsdistinctlysuperiortothose possible with any other material, and on the otherhand,inthesuperiortechnical characteristicsofceramictileascompared withtheothermaterialspreviouslycited.It iscommonknowledge,alsoconfirmedby technicaltestscarriedoutinvarious laboratories,that,ingeneral,ceramicshave ahigherresistancetochemicalattackthan marbleandgranite,arenotsubjecttocuts andscratcheslikewood,linoleumand carpet, and neither burn nor are damaged by directcontactwithfireorincandescent bodies,suchascigarettes.Inaddition, ceramictileareeasytoclean,arenoteasily puncturedandhaveahardnessand resistancetoabrasionwhich,ingeneral,are not found in other materials. FABRICATION TECHNOLOGY AND PRODUCT TYPES The high performance of ceramic tile is the result of extensively studied fabrication technology, alwaysinevolution,whosekeyfeatureistheveryhighfiringtemperaturewhichvaries, dependingontypeofproduct,from950tomorethan1200C.Therawmaterialsforthe productionofceramictilearewidelyavailablenaturalmaterials.Thisisoneofthereasonsfor the relatively limited cost of ceramic tile. The tile body is formed from a mixture of clay (to give plasticity),quartzsand(thenonplasticfractiontogivestructuralstrength)andcarbonatesor feldspars(toprovideafluxingaction).Theglazesareformedfromsand,kaoliniticclay, previouslypreparedglasses(frit),andoxide-basedpigmentstoprovidethecolor.Theraw materialsforthetilebodyarecarefullymixedandground,inordertoobtainaperfectly homogeneousmaterialforshaping.Dependingonthetypeoftiletobeproduced,theprepared mixmaybeintheformofapowderwitha4-7%moisturecontentoraplasticclaywitha15-20% water content. In the first case, the tile are shaped by pressing, with various types of presses and pressures up to 300 kg/cm or higher. In the second case, the clay is extruded through a die of the desired shape. After forming, the tiles must be first dried to remove most of the water and thenfired(inthecaseofunglazedtile)incontinuouslyoperatingkilnsatthetemperatures previously indicated. Physical and chemical transformations take place during firing which give ceramictiletheircharacteristicsocompactness,mechanicalresistanceandphysical-chemical inertness sufficient for the destined use. Depending on firing cycle and raw materials used, tile of varyingcompactnessandporositycanbeobtained.Aswillbediscussedlater,theporosity, whichischaracterizedonthebasisoftheamountofwaterthatthetilecanabsorb,isavery importantparameterwhichalsohasaninfluenceonothertechnicalcharacteristics.Itisworth noting here that the transformations which lead to very compact tile bodies, thus tile with a low waterabsorption,arerelatedtotheformationofanabundantmeltedphaseinthemassofthe bodyathightemperatures,which,duringcooling,solidifiestoformaglassystructure.This processisaccompaniedbyshrinkage,i.e.,afterfiring,thedimensionsofthetilearelessthan beforefiring.Suchshrinkagemeansthereistheriskofacertainamountofdimensional disuniformity and irregularities and the extent of shrinkage will be greater, the lower the value of water absorption that is sought. Inthecaseofglazedtile,twodifferenttechnological sequences are possible after the tiles have been dried: one based on double firing and the other on single firing. In the first case, the dried tilesarefiredandthentheglazeanddecorationsareappliedtotheso-calledbisqueware;the cycleisconcludedbyasecondfiringwhosefunctionistostabilize(fire)theglaze.Onthe contrary, in the case of single firing, the glaze is applied directly to the dried green ware and the glazeandbodyarefiredtogetherinjustonefiringwherethesinteringofthebodyand stabilization of the glaze take place at the same time. At this point in the production cycle, the tiles are sorted, to eliminate defective tiles and separate thehigherqualitytilesfrom those of lower quality as well as to divide them into homogeneous groups according to work size and shade. Thisbriefsummaryofthetechnologicalcyclefortheproductionofceramicfloorandwalltile leads to the following two considerations: Fig.1.1 Technological cycles for the production of the different types of ceramic floor and wall tile 1.Ceramictiles,justasallceramicmaterials,aresubjectedtofiringathightemperatures whichrendersthemstableandinertwithrespecttomostoftheaggressivephysical-chemical action of the environment. The othersideofthecoin,for ceramic tile asforallceramicmaterials,istheir fragility.Ceramictiledonotundergo plasticdeformation,butratherbreak once the limit of elastic deformation has beenreached.Theyalsoaretovery resistanttomechanicalimpact,i.e.,they havepoorresilience.Itshouldbe emphasized, however, that this behavior, whichceramictileshareswithmany othermaterialsandproducts(porcelain chinatableware,drinkingglasses, windowglass,etc.)isnottobe consideredadefect,butrathera characteristicwhichmustbetakeninto considerationforthecorrectuseofthe product. 2.Itispossibletoproduceceramictile withdifferenttechnologicalcycles(e.g., singlefiringordoublefiring),starting fromdifferentrawmaterials(e.g.,white firingorredfiringclays),withdifferent technological solutions for each individual phase of production (e.g., shaping by pressing orbyextrusion)withdifferentoperatingparametersofthemachineryandequipment. Eachoption,eachparameter,correspondstoadifferentproduct(Fig.1.1),with correspondinglydifferentcharacteristicsandlevelsofperformance.Thedifferencesare considerable and can lead to serious problems if one chooses a ceramic tile for a definite application without taking the specific characteristics of the tile into consideration.Thefactthatthedesigner,builder,consumercanchoosefromaverywiderangeof products(forexample,seetheclassificationofceramictileproducesinItalyshownin Table 1.1, based on commercial-product type) is certainly positive, but not without risks. As will be discussed later, there are various defects in ceramic tile floors and walls which can be attributed not to the choice of bad tile, but rather to a bad choice of tile. Theproblem,therefore,istomakeacorrectchoiceoftile,andthustohaveathorough knowledgeofthematerialceramictile.Inparticular,oneshouldknowthetechnical characteristics,whichshouldconstitutethebasisforacorrectchoicebutwhichshouldnotbe considered to the exclusion of aesthetic and decorative criteria. TYPEWATER ABSORPTION (%) SHAPING METHOD MAIN USE GLAZED MAJOLICA COTTOFORTE SINGLE FIREDWHITEWARE SINGLE FIRED REDWARE EARTHENWARE (WHITE BODY) KLINKER 15-25 4-15 0-6 0-12 6-25 0-7 PRESSING PRESSING PRESSING PRESSING PRESSING EXTRUSION Wall tile (internal) Floor tile (internal) Floor tile (internal & external) Floor tile (internal & external) Wall tile (internal) Wall tile (external) Floor tile (internal & external) UNGLAZED COTTO RED STONEWARE PORCELAIN STONEWARE KLINKER 3-15 0-4 0-0.5 0-7 EXTRUSION PRESSING PRESSING EXTRUSION Wall tile (internal) Floor tile (internal & external) Wall tile (external) Floor tile (internal & external) Wall tile (external) Floor tile (internal & external) Table 1.1 Classification of Italian ceramic floor and wall tile according to product type. STANDARDS AND REQUISITES Theworkingconditionsofthetile,i.e.,thestresstowhichthetilewillbesubjectedinthe environment for which it is destined, must first be evaluated by the person choosing the tile, who iscalledupontomakeacarefulandknowledgeablechoiceoftile,fromthewiderangeof products available on the market, capable of reliably resisting the various stresses to which it will be subjected.Knowledgeofthetechnicalcharacteristicsofceramictile,therefore,isoffundamental importanceforanyoneresponsiblefordesigningatiledfloororwall.Oftenthetechnical characteristicsareindicatedinthecatalogues,orinanycasearesuppliedbytheproducer.The determination of these characteristics and the evaluation of the respective performance levels, is carried out and certification made by official laboratories, on the basis of existing standards. The certificate of quality according to recognized standards is the passport for ceramic tile. In order tofullyunderstandthesignificanceandcorrectlyusethisimportanttechnicaldocumentation,it is necessary to have an understanding of the basic structure of the standards.The standard for ceramic floor and wall tile presently accepted in Australia and in other countries of the Commonwealth, is Standard BS 6431. It consists of 23 Parts, corresponding to the 23 EN Standards(EuropendeNormalisation),whosemembersareasfollows:Austria,Belgium, Denmark,Finland,France,GreatBritain,Greece,Ireland,Italy,Netherlands,Norway, Portugal, Spain, Sweden, Switzerland, and West Germany.The structure of Standard BS 6431 is illustrated in Table 1.2, and it includes: -2 general standards -8 product standards -13 standards specifying testing methods. Examples of different types of floor and wall tile.1) Cotto; 2)Earthenware (white body); 3)Klinker 4)Porcelain stoneware; 5)Majolica;6)Red stoneware;7)Single-fired redware;8)Single-fired whiteware; 9)Cottoforte. The general standards form Part 1 (EN 87) which gives definitions, the classification of ceramic tile,alist of the characteristics that the standards take into consideration, marking requirements forpackaging,etc., and Part 23 (EN 163), which establishes the criteria for batching, sampling, inspection and acceptance/rejection of the tile. BS 6431 GENERAL Part 1Definitions, Classification Part 2Sampling PRODUCT REQUISITES Part 2Group A! Part 3Group A IIa Part 4Group A II b Part 5Group A III Part 6Group B I Part 7Group BII a Part 8Group B II b Part 9Group B III TESTING METHODS Part 10Dimensions and Surface Quality Part 11Water Absorption Part 12Modulus of Rupture Part 13Scratch Hardness according to Mohs Part 14Resistance to Abrasion, Unglazed Tiles Part 15Linear Thermal Expansion Part 16Resistance to Thermal Shock Part 17Crazing Resistance Part 18Chemical Resistance, Unglazed Tiles Part 19Chemical Resistance, Glazed Tiles Part 20Resistance to Abrasion, Glazed Tiles Part 21Moisture Expansion Part 22Frost Resistance Table 1.2- BS 6431Standard for ceramic floor and wall tile. WATER ABSORPTION, WA (%)SHAPING METHODI WA