Agglomerate or synthetic stone materials are produced in a controlled factory environment to ensure consistent size, shape and density. As a manufactured product rather than quarried, the surface appearance of agglomerate stone tiles tend to be consistent in appearance being devoid of flaws, veining and colour fluctuations. In addition, the strength imparted by the resin binder often allows for thinner sections to be produced than their natural stone counterpart, thus offering potential weight savings.

Typically, marble or quartz based raw materials are carefully selected and graded to form the basis of the agglomerate stone. The final appearance of the material can be enhanced through the addition of other ingredients, such as mother of pearl, thus giving an extra dimension to the finished product. The components are then compressed under vacuum and vibration, with the stone matrix being bound together using a reaction resin.

Tiles produced from agglomerate stone material start life as a large block, which after curing are cut using industrial saws into unpolished slabs. The slabs can then be further reduced in size and given a variety of surface finishes e.g. honed, polished or anti-slip depending on their intended function.

Care should be taken when installing resin-bonded agglomerates, as there are a number of factors to take into consideration. Extremes of temperature, including sudden changes in temperature, as well as high levels of residual or static moisture should be avoided. Adequate expansion joints should also be incorporated and the correct grade of adhesive must be selected.

Resin bonded agglomerate stone tiles will generally behave differently to ceramic or porcelain tiles when exposed to temperature variations and moisture / water. This may lead to ‘curling’ of the tile. Consequently, it is important to understand the technical characteristics of the agglomerate stone material before it is fixed. The manufacturer should be consulted to ensure that the tile selected is correct for the service conditions expected after installation.

In comparison to ceramic tiling, many manufacturers recommend more frequent movement joints within an agglomerate stone tiled floor, so bear in mind any maximum bay sizes imposed. These bay sizes are often smaller than with ceramic or porcelain tiles and this factor needs to be taken into consideration when planning the tile layout.

Due to the higher coefficient of thermal expansion of an agglomerate stone tile, they may only be suitable for use in internal areas that will not be subjected to extreme variations of hot or cold temperatures, especially where there is the likelihood of a temperature gradient. For example, when tiling behind a large south-facing fully glazed façade the tiles closest to the glass will naturally become warmer than those situated in shadow.

Expansion of agglomerate stone may also occur in the presence of moisture. Therefore, ensure their compatibility with an environment where water contact is likely, such as in a bathroom or shower. In addition, the substrate to which the agglomerate stone tiles are to be fixed must be dry. For example, the moisture content of an existing cement-based screed or concrete must be less than 2% when measured using a carbide hygrometer or 75% RH when using a hair hygrometer. As a general rule, agglomerate stone tiles containing Rosso Levante or Verde Tirreno should not be used in damp areas as they are likely to expand and curl.

Due to the characteristics of agglomerate stone materials, it is prudent to fix them using a rapid setting adhesive. The use of the correct type of rapid setting system will effectively utilize the majority of any mix water in the adhesive curing mechanism, thus preventing moisture contact with the rear of the stone. The use of an additive with the rapid setting cement-based adhesive (two part cement-based) further reduces the water content and increases the bond strength; another important attribute for an adhesive system used with agglomerate stone tiles.

When installing highly moisture-sensitive agglomerate stone tiles, such as Rosso Levante or Verde Tirreno, an adhesive with zero water content should be used, such as an epoxy or polyurethane resin based product.

By Colin Stanyard, Ceramic Product Manager, Mapei UK Ltd