Adhesive strength meets flexibility

Large-format tiles are currently popular in bathrooms. Affixing them properly to walls or floors requires not just good tiling skills, but also the right adhesive. The polymeric binders supplied by WACKER enable adhesive manufacturers and users to meet this challenge.

Bathrooms nowadays are much more than purely functional wet rooms. According to “Schöner Wohnen,” a German home decoration magazine, “feel-good bathrooms” and “personal spas” are right on trend. Especially for those who have the funds and feel drawn to a classy modern look. “The bathroom is second only to the kitchen in terms of greatest financial outlay,” says Dr. Tobias Halbach, director of Technology Management for Construction Polymers at WACKER. “We spend an average of 45 minutes every day in the bathroom, so it should be a well-appointed, welcoming space. Functionality, design and wellness aspects are becoming more important all the time.”

Whether new build or renovation, whether modern, traditional or Mediterranean style – the world is your oyster when it comes to a fit-out. The style is particularly affected by the choice of wall and floor coverings. “All around the world, it is the major manufacturers who determine what is the latest fashion in tiles,” says Halbach. “They set global trends – regional tastes are actually rare.” The WACKER expert also knows the most popular type of tile among consumers in the developed industrial nations: large-format tiles, measuring at least 60 x 60 centimeters. “These look particularly classy, make rooms seem larger and are also more pleasant to walk on because there are fewer joints between them.

The shape, size and constituent material of the tiles dictate the tiling method, the conditions which the substrate must meet and the choice of adhesive to use.

“Large formats are generally harder to handle,” says Armin Hoffmann, a senior technical manager at WACKER. “They are heavier and once they reach a certain weight need two people to carry them. That makes tiling a much more complicated process.” For a start, the walls or floor need assiduous preparation and must be level. “Any irregularity whatsoever in the substrate can put a tile under stress further down the line. And the larger the tile, the greater the risk that it will break,” explains Hoffmann. Large-format tiles are correspondingly more expensive to repair than smaller ones.

Expert handling is therefore just as essential as the right choice of tile adhesive. Binders play a key role in an adhesive, because they boost the bond between the tile and the substrate while also increasing the adhesive’s flexibility. The latter is especially important for very thin tiles just three millimeters thick. These may weigh less in large format, but they are also difficult to handle. “Thin tiles simply break more easily and need to be transported very carefully,” explains Halbach.

When a bathroom is aired for a long time in winter, the tile surface might drop to a temperature of around 0 °C, compared with the 45 °C that shower water can reach. Such are the temperature differences that the system comprising tile–adhesive–wall has to withstand. Consequently, the sandwich layer – the tile adhesive – must not only create a strong bond but also be flexible as that compensates for any stresses. If the adhesive layer were rigid, the tile would crack or fall off. The fact that both thick and thin large-format tiles are susceptible to breaking is also due to the lower number of joints, which are also capable of accommodating stress. Small tiles have a much greater percentage area of joints than their larger counterparts and so cracks are prevented.

No matter whether they are thick or thin, large tiles weigh more and so are more difficult to attach to walls. Here, again, the tiles have to meet particularly high requirements: “You need very good non-slump properties when you are laying large-format tiles. For they allow you to set the tiles exactly where you want them in the adhesive bed,” says Hoffmann. “We can now offer adhesive makers a new binder that features this property and also imparts the necessary degree of flexibility and bond strength. It rounds out our portfolio perfectly.”

VINNAPAS^® 8812 T is a dispersible polymer powder based on a terpolymer of vinyl acetate, vinyl chloride and ethylene that provides adhesives with high water resistance, high non-slump properties and very good workability. As a result, the tiles stick to the wall when the adhesive is still damp, and they can be readily adjusted. Many tile adhesives and troweling compounds require additives in order to achieve strong adhesion or high non-slump properties. These additives are not needed with VINNAPAS^® 8812 T.

As manufacture involves neither plasticizer nor solvent nor film-forming additive, the dispersible polymer powder is also suitable for formulating low-emission tile adhesives for the thin-bed technique. This requires less tile adhesive – and fewer raw materials – and the tilers can work more economically while conserving resources. Wall and floor tiles can be laid up to four times faster by the thin-bed technique than by the thick-bed approach. At an application rate of around 3% dispersible polymer powder, it is also possible to cut down on as much as 90% of the raw materials sand and cement.

A further challenge facing tilers is the adhesive’s open time. This is the length of time during which the adhesive can be worked before it starts setting. Stated in minutes, the open time indicates how much time can elapse between setting a tile in the adhesive bed and attaining a tensile adhesive strength of ≥ 0.5 MPa. The EN 12004 standard on tile adhesives specifies a minimum open time of 30 minutes. Anything longer than that is welcomed by tilers for they can then cover a larger area with adhesive and set the various tiles in place without the compound already starting to harden.

“VINNAPAS^® 8812 T in combination with other additives, such as methyl cellulose, extends the open time substantially and so makes the job of tiling much easier,” says Hoffmann. This is just as important for large tiles as for small ones. Comparative tests in WACKER’s applications laboratory show that the open time can be extended by up to 50%, the exact figure depending on the recipe involved.

No matter which trends emerge within the tile sector in the future, adhesive manufacturers’ recipes will continue to focus on the binders on account of their many talents. Even now, it is apparent that the demands on tile adhesives will continue to rise: for example, we are now seeing the emergence of extra-large formats, i.e. tiles with an edge length of 1.20 meters and more, on the market. “The sector is also addressing sustainability,” says Halbach. “As a raw-materials producer, we are among those working on optimizing our production processes in this regard and on avoiding emissions and boosting production efficiency, for example.”

In order that dry-mix mortar manufacturers can continue to provide tilers with optimum recipes for the full range of tiles available, WACKER offers the services of its specialists, who have the necessary expertise and a wide range of dispersible polymer powders that are being improved all the time. After all, it is not just the tile which depends on the adhesive, but also the functionality, aesthetics and longevity of the bathroom – and thus consumer satisfaction.

Master tiler Markus Ramrath talks about the challenges of laying large-format tiles.

Markus Ramrath: Large formats have edge lengths of 60 to 120 centimeters. Whoever opts for them must reckon on long installation times. This starts with the preparation time, because the substrates need to be very level when large tiles are used. Otherwise, stresses will more easily build up later that can lead to cracks and breaks in the tile. For aesthetic reasons, the joints between the tiles are usually narrow and allow little margin for error or adjustment afterwards. The tiler therefore has to work extremely accurately. The drying times are also longer because the water released from the adhesive during setting has a harder job finding its way out. There are only a few joints, after all, and they are usually narrow. It is important to employ specialty tile adhesives with crystalline water-binding capacity and an increased proportion of polymer to facilitate better curing. Otherwise, there is a greater risk of stresses and breaks were, e.g., objects to fall onto the tiles. Also, tilers need more time to prepare the tiles properly for the room, i.e. to cut them to size and to create holes for fittings and connections.

To simplify your choice, we have summarized our VINNAPAS^® grades into six product classes

L
VINNAPAS^® L class – optimized leveling characteristics
Ensures smooth surfaces with outstanding leveling properties, such as for self-leveling flooring compounds

T
VINNAPAS^® T class – highly thixotropic
Ensures excellent thixotropic properties, as required in thixotropic tile adhesives and smoothing and/or leveling compounds

E
VINNAPAS^® E class – improved properties
Enhances the properties in many applications, resulting in greater ease of processing, adhesion and water resistance

N
VINNAPAS^® N class – neutral effect on rheology
Ensures a high level of formulation flexibility and a diverse range of applications

H
VINNAPAS^® H class – hydrophobic excellence
Ensures notable hydrophobic properties in all kinds of plasters, grout mortars and external thermal insulation composite systems (ETICS/EIFS)

F
VINNAPAS^® F class – superior flow properties
Ensures outstanding flow properties without the addition of synthetic superplasticizers or casein; suitable for self-leveling flooring compounds that require immediate liquefaction and a specific rheology