Manufacturing Tolerances for Ceramic Tiles

Ceramic Tiles are generally manufactured to conform to the European Agreed Standard, of which the English language version is BS-6431 or the newer ISO/DIS 10545. Both specifications use the water absorption characteristic to define product type, as water absorption is a commonly related item for all tiles, whether wall, floor,  pressed, extruded, glazed or unglazed.

Contrary to popular belief, Ceramic Tiles are not perfect and are allowed to vary slightly in dimension and appearance (within the standard) and still be classified as first quality product.

It is important to note that these tolerances have been set taking into account the characteristics inherent in natural products such as the clay, that is kiln fired in the case of ceramic tiles.

TILE CLASSIFICATIONS

BS6431 Tile Classification
METHOD OF MANUFACTURE WATER ABSORPTION
0 ≤ 3% 3 ≤ 6% 6 ≤ 10% 10 > 20%
EXTRUSION A1 A11A A11B A111
DUST PRESSING B1 B11A B11B B111

 

ISO/DIS 10545 Tile Classification
METHOD OF MANUFACTURE WATER ABSORPTION
0 ≤ 0.5% 0.5 ≤ 3% 3 ≤ 6% 6 ≤ 10% 10 > 20%
EXTRUSION A1A A1B A11A A11B A111
DUST PRESSING B1A B1B B11A B11B B111

As an example, in the broad sense, tile types fit the following groups:

Extruded Unglazed Tiles    = Groups A1, A11A, A11B or A1A, A1B, A11A, A11B

Glazed Mosaic                     = Groups B1 or BIA, B1B

Glazed Floor Tiles               = All Groups but rarely Group B1A or B111

Glazed Wall Tiles                = B111


Manufacturing standards are divided into two categories: Surface Quality Characteristics and Physical Properties

Surface Quality Characteristics

  • Length & Width: Dust pressed tiles larger than 95 x 95mm are allowed a deviation of + or – 0.5%.  Therefore 300 x 300mm tiles can range from 298.5mm to 301.5mm, (a combined variance of 3mm overall between two tiles) and still be within the accepted standard.
  • Thickness
  • Straightness of sides: All of these characteristics have allowable tolerances
  • Rectangularity        
  • Surface Flatness
  • Surface Quality: It is permissible for up to 5% of a lot to have visible surface defects and the lot still be classified as first quality.

Physical Properties

It is important to understand the Physical Properties of Ceramic Tiles to properly recommend their use.

The most commonly required characteristics are:

  • Abrasion Resistance (P.E.I. Rating)

How a glazed ceramic tile surface will perform when subject to continuous wear is most important when considering selection of any floor tiles.  The standard for Abrasion Resistance measures the degrees to which a floor tile’s surface will withstand friction such as is the case with the continual wear of foot traffic.

Abrasion Resistance is determined by abrasion tests developed by the Porcelain Enamel Institute of America which has become known as the P.E.I. test.  This test involves the rotation of steel ball bearings on the surface of a tile for a given number of rotations.  Wear is assessed by viewing through a special chamber.  The test method currently classifies tiles at the number of revolutions at which the abrasion can be readily distinguished.

P.E.I. Rating No of Rotations Classification Suitability
1 150 No Traffic Group 1 tiles are suitable for wall applications only.
2 600 Light Traffic Group 2 tiles can be used on residential interior floors, but should not be used in areas such as kitchens, entry ways and stairs that are subject to tracked in or spilled abrasives.
3 750 Moderate Traffic

 

Group 3 tiles can be used for any residential or light commercial application. The only place that they are not recommended is in heavy traffic commercial areas, like banks and restaurants.
4 2100 Moderate-Heavy Traffic Group 4 tiles can be used for any residential and most commercial applications. These tiles are durable enough to be used in such heavy traffic areas as shopping malls.
5 >12000 Heavy Traffic Group 5 tiles are the most durable and can be used for all residential, commercial, and even industrial applications where extreme durability is a must.
  • Scratch Hardness (MOH’s Scale)

How a Ceramic Floor Tiles glaze or surface performs when subject to scratching when items are dragged across its surface is also most important when considering selecting floor tiles, particularly high gloss floor tiles.

Scratch Resistance is determined by scratch tests and measured under the MOH’s Scale whereby tiles are ranked from 0 to 10 in order of hardness. For example:

0 = Talc

1 to 9 Are assigned various natural minerals corresponding to their relative hardness (8 = Topaz)

10 = Diamond (hardest material know to man)

Although most ceramic floor tiles fall within a narrow range on the MOH’S Scale, it is useful to know which tiles have the higher rating.

  • Slip Resistance

A separate standard (AS/NZS 4586) exists for the classification of the slip resistance for Ceramic Tiles.  This is primarily used for the use of Ceramic floor tiles in public applications such as shopping centres, office foyers etc.

  • Water Absorption (Impact Resistance)

The degree to which a Ceramic floor tile is resistant to chipping, staining and acid resistance is determined by the degree to which it absorbs water.  High water absorption corresponds to a porous structure whilst compact, vitrified structures have low water absorption.

Generally the lower the water absorption factor the more resistant the tile is to chipping, staining and chemical attack.

Water Absorption Categories:

Water Absorption Factor Tile Type
Less than 0.5% Extremely low water absorption Impervious Tile
0.5% to 1.0% Very low water absorption Fully Vitrified Tile
1.0% to 3.0% Low water absorption Semi Vitrified Tile
3.0% to 7.0% Medium water absorption Normal Ceramic Body

Note: Because of their hardness highly vitrified tiles are usually:

  • More difficult to cut (due to their greater tensile strength) and often require diamond cutters.
  • Require specialised adhesives correct installation.