New Technology in Flooring: Strong Stain Resistance for Cement-Based Floors

A new silane-based binder provides highly effective protection against permanent stains on cement-based floors. SILRES ® BS 6920 offers significantly superior stain protection compared to conventional products. Product performance has been validated through initial reference applications and real-world examples. An increasing number of architects, contractors and real estate investors have begun using concrete or cement-based floors in visible areas. When ground and polished, such floors successfully meet rigorous aesthetic expectations. These specially designed floors are now found in many fashion boutiques, exhibition and showroom spaces, shopping centers, bistros, galleries, museums and even residential properties. Cast terrazzo floors bound with cement are also regaining attention. The common disadvantage of concrete, cement screeds and cement-based cast terrazzo floors is that their surfaces are porous and permit liquid penetration. As a result, they soil very quickly, and removal of absorbed liquids and stains is extremely difficult. Their porous structure also reduces the mechanical strength of the floor. If the expectation is that cement-based floors maintain their value and appearance over the years, these floors must be protected against lime and wear before they are put into use. The protection methods available for floors vary depending on the expected wear level and aesthetic requirements. The technique commonly used to protect specially designed cement floors is impregnation.

Protection Through Impregnation

Various technologies are used in impregnation agents for cement-based floors. Silicate-based water-based products and solvent-containing silane-based products are among the most frequently encountered options. However, as determined by companies in the construction materials industry and confirmed by Wacker laboratory tests, many common stain sources challenge both of these technologies. Thanks to Wacker's new SILRES ® BS 6920 product, manufacturers now have access to a specialized product whose highly effective additives can be incorporated into impregnation products or thin coatings for use on cement-based floors. These additives significantly reduce susceptibility to staining while strengthening surfaces.

Alpha-Silane Technology for Rapid Cross-Linking

The new binder belongs to a class of materials called α-silane polyethers. In these hybrid polymers, silane units are located at the ends of polyether chains; these units also contain alkoxy groups (Figure 1) and cure through silane cross-linking. Their structure permits very rapid cross-linking of these polymers even in the presence of minimal catalyst quantities. [1,2,3] As soon as atmospheric moisture acts on the polymers, catalyzed α-silane polyether formulations deposit from outside inward and rapidly form a siloxane network.

Figure 1: Structure of an α-dimethoxysilane-terminated polyether: Each of the two silane ends is bonded to the polyether backbone through a methylene group (red) and a urethane unit. In this type of linkage, the silicon atom is in the α position relative to the urethane nitrogen atom. (Graphic: Wacker)

In practice, the cross-linking rate of the new binder is adequate if the formulation contains an aminosilane catalyst. N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (GENIOSIL® GF 9) has proven to be the optimal choice, an aminofunctional silane. The compound also functions as an adhesion promoter. The new α-silane polyether has been optimized for use in impregnation agents for cement-based floors. The chemical structure of the silane modules and the length of the polyether chains are adjustable parameters. For example, the silane modules have been modified to form a particularly tightly structured network composed of quartz-like structural units upon curing. As a result of this optimization work, a new, low-viscosity binder has been obtained that penetrates deeply into the pores of the cement-based surface, fills these pores, and cross-links to create a hard material. The cured product is non-flammable. The chemical structure of the binder makes the treated cement-based surface both hydrophobic (water-repellent) and oleophobic (oil-repellent), thereby significantly reducing the surface's susceptibility to staining. The quartz-like structure of the cross-linked binder mechanically strengthens the surface, enabling the treated floor to withstand heavy pedestrian traffic and even allow the use of forklifts, cars and trucks on it.

Versatile Processing Options

The viscosity of the new α-silane-terminated polyether – 75 mPa.s – is equivalent to the viscosity of olive oil. The volatile organic compound (VOC) concentration is below 0.5%. The low VOC content is due to cross-linkable alkoxy groups that release a short-chain alcohol in free form during curing. The new product contains no solvents or plasticizers, is odorless, is not classified as a hazardous substance, and has a flash point above 100°C. In other words, SILRES® BS 6920 can be used safely. Even the simplest mixers can be used to process this new binder into one-component formulations for application to cement-based floors. It is recommended to add UV stabilizers to obtain suitable UV stability for existing thin coating and/or impregnation applications. The next step is to mix in the final component, the catalytically active aminosilane. In general, the product becomes moisture-sensitive after catalyst addition. These one-component, ready-to-use products can be stored in sealed containers for up to one year. SILRES® BS 6920 can be formulated in different ways: The product can be processed without solvents; alternatively, the viscosity of the mixture can be reduced by adding an appropriate reactive diluent that does not compromise the solvent-free and odorless characteristics of the ready-to-use final product. Isooctyltriethoxysilane is an example of a suitable reactive diluent. During formula preparation, ground quartz, pigments and other solids can be added to generally alter the mechanical and optical properties of the cured final product. When no solid material is added, the formulated products are transparent and produce a high-gloss surface on cement floors. Table 1 shows a solvent-free reference formulation that produces a transparent impregnation or thin transparent coating depending on the coating weight. For such formulations, the open time is approximately 20 minutes and the tack-free time is 30 minutes. The addition of a reactive diluent can extend the processing time to up to two hours.

Table 1: Solvent-free reference formulation for transparent concrete impregnation

Easy to Apply

Final products prepared with the new binder can be applied to clean, polished floors using a mop, short-pile roller or airless spray gun. Curing is largely complete after twenty-four hours, and from that point the floor can be walked on or other operations can be performed. Best results are generally achieved with two-coat application, particularly for highly absorbent surfaces. When the product is applied to such a surface, the first coat largely fills the pores and strengthens the floor. Since most of the material is absorbed by the surface, the treated surface has a non-uniform, blotchy appearance. Following application of the second coat, a uniform surface with a fine, high-gloss film suitable for polishing is obtained. From an application standpoint, it is worth noting that SILRES® BS 6920 is a product designed for impregnation. According to DIN EN 1504-2 standard, the thickness of the film formed on the surface after impregnation can reach 100 μm. Studies have shown that depending on the absorbency of the floor, the total coating weight (sum of both coats) should not exceed 100 to 150 g/m². The low coating weight demonstrates the economic benefits of applying this new and important technology. Because products prepared from the new binder contain an aminosilane, they adhere very well to cement surfaces even without prior priming. This has been confirmed by pull-off adhesion strength tests performed with a reference formulation applied in two coats over concrete slabs. The average pull-off adhesion strength value obtained was 5.79 N/mm². Adhesion to glass and many metals is also good. If the treated surface becomes damaged during use, the existing product can also be used for repair and, if necessary, polishing of that area.

Stain Resistance, Color Intensification, Surface Strengthening

Impregnation with SILRES® BS 6920 produces a three-way effect: it protects cement-based floors against permanent stains, intensifies color, and strengthens the surface. These effects have been confirmed by treating cement-based test panels with the reference formulation (Table 1) for testing purposes and by performing localized applications on cement floors. Stain-prevention properties were tested by comparing products on test panels and floor test specimens. In this study, the stain-prevention properties of the reference formulation were compared with silicate and silane-based impregnation agents available on the market. The study used twenty substances, including salt water, cola, mustard, ketchup and used oil (Figure 2). These substances were allowed to be absorbed into the surface for twenty-four hours, then wiped with dry and subsequently damp paper towels. On surfaces impregnated with silicate, fourteen of the twenty test substances left stains. With solvent-based silane impregnation, this number dropped to seven, and on surfaces impregnated with SILRES® BS 6920, only three substances left stains (Figure 3). A video of SILRES® BS 6920 on YouTube shows how the tests were conducted and explains the results [4]. Figure 2: Stain test: Twenty substances were tested, including salt water, cola, mustard, ketchup and used oil. These substances were allowed to be absorbed into the surface for twenty-four hours, then wiped with dry and subsequently damp paper towels. (Photo: Wacker) Figure 3: Results of the comparative test on cement-based test panels (stains caused by test substances are circled in yellow). The panel impregnated with silicate (left) shows significantly more stains compared to the panel treated with a silane (middle). The panel impregnated with SILRES® BS 6920 (right) retains only three stains that cannot be removed. (Photos: Wacker) In other words, SILRES® BS 6920 provides far more comprehensive protection against staining compared to conventional products, and when cleaned within a day, even common spills leave virtually no trace. Only highly acidic and highly alkaline environments challenge the limits of this new technology. SILRES® BS 6920 also significantly intensifies colors (Figure 4). Impregnation of a cement floor with a transparent product formulation allows the aggregate materials in the floor to visually stand out.

Figure 4: SILRES® BS 6920 significantly intensifies color. (Photo: Wacker)

Surfaces become more resistant to wear and scratching after treatment with the new SILRES® BS 6920. For example, when subjected to the rotating wheel test described in EN 13892-5 standard, samples treated with a thin coat containing SILRES® BS 6920 resulted in only 3 g of material collected from wear, whereas 40 g of material was collected from untreated panels (Figure 5). These results demonstrate how effectively the new binder strengthens cement-based surfaces.

Figure 5: SILRES® BS 6920 strengthens floors. Measurements according to EN 13892-5 show that the amount of material removed by abrasion from concrete test panels impregnated with a SILRES® BS 6920-based formulation dropped from 40 grams (left column) to 3 grams (right). (Graphic: Wacker)

Initial Reference Applications

Reference projects are being implemented in which cement-based floors are impregnated with SILRES® BS 6920. One of the first applications for which observational data is available is the jam manufacturing facility of Agricolae Kft. located in the city of Jánkmajtis in northeastern Hungary. The project's objective was essentially the renovation and protection of the 390 m² production hall floor used for filling and labeling glass jars containing marmalade and other preserves. The work was performed by Durostone Kft., an industrial floor restoration specialist based in Sóskút, Hungary. The existing floor had a worn epoxy coating. Durostone recommended removing the severely damaged epoxy resin layer and treating the concrete floor with SILRES® BS 6920.

Project Preparation and Implementation

The old epoxy resin layer was completely sanded to expose the flat, well-conditioned untreated concrete floor. The impregnation process was carried out on two consecutive days in early June using a mixture containing 95% SILRES® BS 6920 and 5% GENIOSIL® GF 9. Because the hall had no windows, UV protection was not used. For the first coat, the product was diluted on-site with 10% reactive diluent. The applicators used approximately 50 g per square meter of the diluted formulation and immediately observed color intensification (Figure 6). Although the diluted impregnation agent penetrated the absorbent floor easily, the surface appeared blotchy. The diluted product tack-free time was approximately two hours, and full curing of the first coat took seven hours.

Figure 6: Diluted SILRES® BS 6920 was applied to the ground concrete floor of the production hall at Agricolae Kft. jam manufacturing facility in Jánkmajtis, Hungary. (Photo: Wacker)

The applicators returned the next day after an 18-hour interval to check whether the surface was still tacky. The surface was not tacky; therefore, they proceeded to the second application using the undiluted formulation, again at 50 g/m² concentration. When the second coat was complete after six hours, a stain-free, uniform, high-gloss surface was obtained (Figure 7). The applicators reported that the impregnation agent was easy to apply in both diluted and undiluted form. They also praised the product's natural odor.

Figure 7: Production hall at Agricolae Kft. facility following application of the second coat of SILRES® BS 6920. The floor surface now has uniform gloss and permanent protection against stains. (Photo: Wacker)

Conclusion and Future

For impregnation of cement-based surfaces, there is now a highly effective alternative to silicates or silanes: SILRES® BS 6920, a solvent-free, silane-based new binder that is not classified as a hazardous substance and is processed without difficulty. Its stain-prevention properties are far superior to conventional binders. Cleaning and maintenance of floors treated with formulations based on the new binder are easy and cost-effective. Typical applications include cement-based floors found in galleries and sales areas, restaurants, train station buildings, event and exhibition halls, museums, private residences, underground parking facilities, logistics centers and production facilities. Although use has thus far been limited to interior spaces, exterior applications are currently being tested. Dr. Udo Anders Technical Marketing Manager Construction Chemicals Wacker Silicones     Udo Goedecke Marketing Manager Construction Chemicals Wacker Silicones  

References [1] W. Schindler: Feste Verbindung. Alphasilanterminierte Polyether ermöglichen schnell härtende elastische Verklebungen. ["Strong Bond: Alpha-Silane-Terminated Polyethers Enable Rapid Curing of Elastic Adhesives"] Farbe und Lack, 2006 (10), pp. 44-49. [2] K. Bichler, L. Zander: Innovative Hybridpolymere für hochfeste Klebstoffe. Alphasilanterminierte Polyether. ["Alpha-Silane Terminated Polyethers: InnovativeHybrid Polymers for High-Strength Adhesives"] Adhäsion, 2012 (9), pp. 32-36. [3] K. Bichler, A. Bauer: Niedrigviskos, schnell vernetzend. Neue Bindemitteltechnik für Flüssigabdichtungen. ["Low-Viscosity, Fast-Curing: New Binding Agents Technology for Liquid Seals"] Farbe und Lack, 2013 (4), 129-133. [4] https://www.youtube.com/watch?v=fSUmkkFFjr4