Agglomerate or resin agglomerated tiles have become an increasingly popular floor finish in recent years. The reason is simple; they offer a cost-effective alternative to natural stone.
Agglomerate is a term used to describe a manmade stone or tile product that usually consists of stone pieces and/or aggregates held together in a synthetic binder, such as a polyester resin or epoxy resin. In some cases, the type of binder may have a profound effect on the behavior and performance of the agglomerate product. Polyester resins have a high coefficient of thermal expansion(Y) and may present problems concerning significant differential movement when installed in exterior installations such as building facades.
There are thousands of different agglomerate products on the market, and each of these tile types has its own physical characteristics, dependent on the type of stone chips or aggregates (e.g. color and inherent physical properties of the stone), type of binder, dimensional stability of the aggregate, and percentage of each material used. The most widely used agglomerate tiles typically consist of stone pieces mixed into a 4% to 8% polyester resin binder.
As the production technology and capabilities of agglomerate tile increases, so do the size, thickness and composition. Agglomerate tile can be found in many sizes, with larger formats such as 90 x 90 cm. However, even larger agglomerate slabs are now being produced in sizes of 90 x 180 cm or greater.
It is important to note that the facial dimensions and thickness of agglomerate tile have a direct bearing on the dimensional stability. Some agglomerate tile manufacturers issue a table or chart listing which products are suitable for use with normal setting materials, and which require rapid setting materials or 100% solids epoxy setting materials.
It is important to check with the agglomerate tile manufacturer to verify suitability and acceptability of each agglomerate tile for its intended purpose. For instance, certain agglomerate tiles may not be suitable on an exterior application due to moisture sensitivity, instability of some resin and stone pieces to extreme temperature changes, non-ultraviolet light (UV) resistance or due to freeze/thaw restrictions. It is also a good idea to check with the manufacturer for recommendations on setting materials.
The manufacturer may also have requirements on the moisture vapor emission rate (MVER) of the mortar bed or concrete prior to installation of their tile, and may even prohibit the installation of their product using traditional sand and cement methods. It is always a good idea and highly recommended to conduct a test area in the actual conditions, and with the specified installation materials, to determine acceptability of all materials and conditions.
Agglomerate tiles are manufactured in a broad array of colors and can be engineered to offer technical benefits, notably improved mechanical and physical properties, such as scratch resistance and flexural strength. This manufacturing process combines a mixture of crushed marble or stone chips and powdered stone, together with colors, and polyester resin as the binder. The dry materials are combined and the resin and hardener are added to make a mass that is placed in an enclosed chamber and put under negative pressure, using a vacuum pump, to remove air bubbles.
After the polyester resin reacts, it binds the entire mass into a solid block that is then cured and sliced into tiles and slabs. These tiles and slabs are further processed by polishing the front and grinding the back to a uniform thickness. Slabs can also be cast by this process, and will be processed by grinding and polishing to produce niched slabs with the appearance of marble or other stone, but at a more economical cost than natural stone cut from block.
Normally, the back of all the agglomerated stone is passed through a grinder to gauge the material to a uniform thickness and to remove all irregular protrusions. The thickness is normally gauged accurately within +/- 1mm. This conglomerate stone material is used, worked and installed just as natural stone tiles or ceramic tiles. Slabs cut in the larger sizes are used for floors and walls similar to natural granite or marble slabs. They are marketed under a bewildering range of generic names, including conglomerates, resin agglomerated tiles, engineered stone (particularly in the U.S.), reconstituted stone and re-composed stone.
There are two main types of polymer-resin binders used in the manufacturing of agglomerate tiles: epoxide or polyester. Typically, the ratio of resin binder to agglomerate varies from 4% to 8%, which means they also contain 92% to 96% agglomerate. It is a general rule that the higher the percentage of resin present, the lower the abrasion resistance. The proportion of resin also affects the tile’s coefficient of thermal expansion(Y).
This is important to note due to the increase of underfloor heating (UFH), which is becoming a popular heating choice within the UK. When considering a rigid tile niche over UFH, it is important to understand how the heat change affects the different materials employed within the tiling installation.
Agglomerate tiles generally have a higher coefficient of thermal expansion(Y). In simple terms, the tile has a high modulus of rupture, or measure of strength before rupture, and is being “restrained” by the tile adhesive. However, due to heating and cooling cycles, a relatively small amount of heat expansion and contraction can exert a high level of stress on the tile adhesive. And the larger the tile, the greater the magnitude of the dimensional changes on resin agglomerated stone caused by the thermal expansion or temperature increases.
It is also important to note that resin agglomerated stone tiles have varying degrees of moisture sensitivity. This means that these tiles can also be susceptible to differential moisture expansion. In severe cases, this can lead to “curling” of the tiles.
According to the technical document, “Tiling with Resin Agglomerated Tiles,” released by The Tile Association (TTA), “Cementitious floor screeds to receive resin agglomerated tiles should be completely cured and tested to ensure that they have a moisture content of not more than 2% by weight or 75% relative humidity using the appropriate test equipment and that an appropriate adhesive is chosen.” This means that the use of a cementitious-based tile adhesive or screed will introduce moisture directly beneath the resin agglomerated stone tile which may be taken up slowly by the tile. Some loss of moisture will occur when the tile joints are unfilled, although this process will be slower.
Agglomerate tiles come in a variety of formats, but the larger the format, the more likely moisture will become trapped at the tile/adhesive interface. In the case of some resin agglomerated tiles, this will increase the risk of curling.
It is common practice for the manufacturer of large-format tiles to fix a reinforcing mesh to the underside. Consideration must be made to the type of adhesive used to fix the mesh, ensuring it will not have an adverse effect on the adhesive bond. British Standards Institution (BSI) BS 5385-3 recommends that the mesh on the back of the tile should not obscure more than 25% of the total surface area. If it does, at least 75% of the mesh must be removed or the tiles be mechanically fixed. BS 5385-3 also recommends that resin-based agglomerated stone tiles should not be used externally. Therefore, the correct selection of tile adhesive is essential when fixing agglomerated tiles; advice must be sought from the tile manufacturer or supplier.
Adhesive selection guidelines
Agglomerate tiles are neither classed as ceramic nor natural stone. British Standards Code of Practice, BS 5385, states “To avoid moisture from the adhesive bed distorting resin-based agglomerated stone, reaction resin adhesives, or quick drying low alkalinity cement-based adhesives should be used.”
When installing a ceramic tile or natural stone tile using a tile adhesive, the accuracy of a subfloor should be such that when placing a 2-meter straightedge on the floor, there is no gap greater than 3 mm. If this is not the case, this may be rectified using a suitable smoothing or leveling compound prior to the tile installation.
In the case of fixing large-format tiles, in particular resin agglomerated stone tiles, the surface regularity should be SR1 or better for both the wall and floor substrates.
The tile adhesive should be applied using a suitable notched trowel to the wall or floor and additional back buttering of the tile with the tile adhesive to ensure a full solid bed and adequate adhesive coverage.
When placing resin agglomerate tiles on walls and floors, solid bed fixing is essential to ensure full contact between the tile adhesive and the tiles and to eliminate voids beneath the tiles.
Conglomerate tiles are not recommended for use in frequently wet areas such as wet rooms, walk-in showers and swimming pools. For domestic showers and wet rooms, specifiers should seek advice from the tile supplier or manufacturer with respect to their suitability in these applications. It is also important to establish what, if any, additional precautions may be necessary to take both during and following completion of the tiling installation. Fundamentally, the wall and floor background substrates should be protected from moisture ingress or leaks by using a suitable waterproofing tanking system such as Laticrete Hydro Ban.
Additional protection from potential water ingress may be afforded by using a suitable impervious reaction resin grout (e.g. Laticrete Spectralock Pro Premium Grout), although the use of impervious grouts and adhesives is no substitute for a tanked installation.
The need for inclusion of movement control joints within any tiled installation is explained in the BS 5385. Any movement, such as drying shrinkage, thermal expansion/contraction and moisture movement, will generate stresses within the tiling system which can lead to de-bonding or cracking of the grouting and/or tiles.
Where the resin agglomerate tile is deemed to be suitable for floors subjected to direct heat or heat from an environmental source, the “Tiling with Resin Agglomerated Tiles” document from TTA recommends the frequency of movement joints be increased. For example, BS 5385-3 advises that for floors subjected to significant thermal changes, the floor area should be divided into bays of size not greater than 40 square meters with an edge length not greater than 8 meters. However, TTA technical document, “Tiling with Resin Agglomerated Tiles,” recommends the floor area should be divided into bays not exceeding 25 square meters to allow for the anticipated increase in thermal expansion of the resin agglomerated tiles with UFH. Under normal dry internal conditions, the advice is that bay sizes should be reduced to not exceed 36 square meters.
It is always advisable to use white adhesives for installing white or light-colored agglomerate tile. In all cases, proper substrate preparation and attention to detail is paramount to a long-lasting and problem-free installation. Attention to details will minimize lippage, reduce moisture-related concerns and eliminate problems caused by poor choice of setting materials. It is recommended to verify the suitability and acceptability of the installation system by conducting a test area, and to provide peace of mind for the architect, general contractor, tile contractor and building owner.