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