A Carpet Made of Grit and Gravel

Floor coverings made of stone granules and synthetic resins can be laid without joints, are resilient, and easy to process and clean. They are increasingly being installed not only in commercial premises, but also find their way into living areas. With SILRES^® BS 6920, WACKER offers a well-adhering and solvent-free binder for such floors.

The fact that carpets do not necessarily have to be made of textile, but can also be made of granite or quartz, first came to the attention of Susanna and Dr. Klaus Hock eleven years ago. In 2012, the couple, founders of the eponymous family business S u. K Hock from Regen in the Bavarian Forest, received an inquiry from a customer: He was looking for a suitable synthetic resin to repair what he called stone carpets. This term refers to the fact that like a carpet, the flooring covers the substrate without joints, as is the case with tiles, for example. Stone carpets usually consist of 95 to 96 percent by weight granite chips, quartz or marble pebbles, which are fixed by a binder – a synthetic resin.

When Susanna and Klaus Hock were confronted with the request for a suitable binder for stone carpets, they had already been specializing in synthetic resins for several years. Klaus Hock, who holds a doctorate in chemistry, and his wife Susanna ventured into self-employment in 2004 and, like so many start-ups, began small – in their private garden shed, which they converted into a laboratory. Since then, they have been researching, developing and consulting in the field of synthetic resins on behalf of a wide range of industrial companies.

Already in 2006 the garden house became too small and the first production hall was built in Regen. In 2010, the young company also opened an online store through which private customers, small businesses and reprocessors can order synthetic resin systems.

In response to the request for binders for stone carpets, S u. K Hock developed special resin formulations suitable for this application. “In the beginning, these binders were based exclusively on epoxy or polyurethane resins,” says Franz-Josef Hock, son of the two founders and now the company’s commercial director.

The resin specialists from Eastern Bavaria are flexible regarding the underlying chemistry of the binder: Based on their decades of experience, they also offer polyacrylic, silicone and polyester resins and have the relevant expertise. The decisive factor is what works best for each application, Hock emphasizes.

For stone carpets, S u. K Hock now explicitly promotes its resin systems based on SILRES^® BS 6920 from WACKER, a binder based on WACKER's patented α-silane technology. These hybrid systems combine the typical properties of silicones (for example, high elasticity) and polyurethanes (such as mechanical strength), but unlike the latter, they are free of potentially harmful isocyanates, tin catalysts and solvents.

“The advantages over conventional resins for use in stone carpets are considerable,” Franz-Josef Hock is convinced. First of all, there’s the very simple processing, because it is a one-component binder. The flooring installer only needs to mix the pebbles and liquid binder and apply it evenly to the primer. The primer consists of a thin layer of the pure binder applied to the clean substrate. It ensures good adhesion of the stone carpet.

One of the advantages of SILRES^® BS 6920-based binders is that they are more tolerant of substrate moisture than other systems. Because the layer that forms is breathable and permeable to water vapor, allowing the residual moisture of the substrate to escape. “That’s why we sometimes jokingly call SILRES^® BS 6920 ‘GORE-TEX^® for concrete’ - in reference to the textile industry,” says WACKER chemist Udo Anders.

Another advantage the new binder offers is rapid curing. The stone carpet is open to foot traffic just three to four hours after application. “For the craftsman who is laying the stone carpet outdoors, for example, this means he can leave the construction site calmly at 4 p.m., even if rain is forecast at 7 p.m.,” explains Franz-Josef Hock.

Hock’s resin systems based on SILRES^® BS 6920 are also completely free of organic solvents. They are also more conducive to ensuring occupational health and safety than resins based on epoxy or polyurethane resins. “Incorrect use of competitors’ systems can trigger respiratory sensitization and allergies,” notes Udo Anders. In fact, craftsmen who work with polyurethane-based synthetic resins will have to provide proof of safe use and handling training in the European Union from August 2023.

Just as there are both wall carpets and normal carpets, stone carpets made of silane-modified hybrid polymers based on SILRES^® BS 6920 can also be used as wall coatings. “In this case, the formulation of the resin must then be adapted to this application,” explains Udo Anders. Such wall formulations are adjusted by adding appropriate auxiliaries to prevent run-off from a wall when the material is applied to it.

WACKER calls its α-silane technology hybrid polymers because in these molecules, such as in SILRES^® BS 6920, an organic polymer is linked to an organofunctional silane, thereby enabling targeted control of the system’s properties. Hence the name hybrid binder: hybrids are things or living things of mixed origin that arise through mixing or crossing two different components or beings.

WACKER first presented SILRES^® BS 6920 to specialists in 2017 as a raw material for the hydrophobic impregnation of mineral substrates, such as concrete floors. SILRES^® BS 6920 adheres well to cementitious surfaces and cures rapidly when exposed to atmospheric humidity, forming a stable, resilient siloxane network. The surface becomes water repellent and stain resistant.

Because of the way stone carpets are structured, they don’t show up stains as readily as concrete or other floors. Nevertheless, the good stain resistance of SILRES^® BS 6920-based coatings also has a positive effect on stone carpets. “Hybrid resin stone carpets are easier to clean than those with polyurethane or epoxy resins,” says Franz-Josef Hock. The surface structure depends strongly on the size and texture of the stones used.

As a young family man, he appreciates the benefits of easy cleaning. Apart from their prominent place in his profession, stone carpets have also become part of his personal life: they are an established feature of Hock’s home – covering a small water playground for his two children, a walk-in shower, an entrance landing and a roof terrace – and they have to be kept clean.