Mechanical strength of ceramic tiles: an index not to be underestimated

What is strength

For ceramic porcelain stoneware floor tiles, bending strength is the perfect indicator of mechanical strength.
It is associated to the force by which a tile responds when subjected to stress which can break it.
It is a load limit value applied to three points which the ceramic or porcelain stoneware tile can bear without breaking.

When are ceramic tiles subject to bending

Porcelain stoneware tiles are subject to bending when they are not continuously bonded to the substrate: because the bonding layer is not uniformly distributed, for example, or because the substrate is weak or inconsistent. In these cases, the tile has to cope with an undue load-bearing function and can even break.

How is bending strength quantified

Bending strength is quantified by two entities:

1. the force required to break the tile in half, which depends both on the material the tile is made with and its shape and size.

2. flexural strength, which depends exclusively on the tile micro structure, i.e. its ceramic mass.

How is strength measured

The international method for measuring strength is given in standard UNI EN ISO 10545.4 and applies to all ceramic and porcelain stoneware tiles.
Using this method, every tile in the test batch is placed on two rollers, while increasing force is applied by a third roller along the whole middle line of the working surface until the tile breaks.

As the breaking value also depends on the shape of the tile, the standard requires that it is not directly the force, F which is calculated, but rather the breaking strength, S:

S = FL/b

i.e. breaking strength = force, distance between rollers/tile width

When do we measure the strength of a ceramic floor?

Strength is usually measured at the end of the production cycle, before product selection and packaging. This measure is required also when tiling is broken or cracked, and is used to check the quality of the product and its technical characteristics relating to external stresses.

Strength is highly important for both design and process controls.