Cleaning and Maintaining Natural Stone

Natural stones with the same or similar look can have very different technical properties, particularly with regard to sensitivity to alkalis or acids, hardness, and water absorption. It is these factors which determine which stone is suitable for which purpose and how it must be maintained in order to retain its appearance for a long time. Before cleaning, you must therefore have thorough knowledge of the stone's properties based on its mineral composition and surface treatment, as well as its usage.

Knowing Natural Stone Properties

Natural stones are used in many different areas, including commercial industry, landscaping, building facades, masonry, and interior finishing, where they are frequently used as floor coverings. They are first mined in quarries and sawed to size in stone-processing operations. Their surfaces are then treated using mechanical methods—whether polishing, flaming, honing, or sandblasting. No synthetic material offers such versatility in colors and surface finishes. Natural stones with a similar appearance can have completely different technical properties, particularly regarding their sensitivity to alkalis or acids, hardness, and water absorption rates. These factors determine which stone is suitable for a specific environment and how it must be maintained to retain its appearance over time.

Natural stones can be classified into hardness levels based on technical processing criteria: Hard rock (such as gneiss, granite, quartzite, basalt, and gabbro), medium-hard rock (such as marble, fossiliferous limestone, and serpentine), and soft rock (such as sandstone and slate).

A worker cleans floors with natural stone using a Kärcher compact walk-behind floor scrubber

The way in which a stone is processed also has an impact on the cleaning requirements. Polished floor coverings made of medium-hard stone can become dull if alkaline cleaning detergents with a pH value of over 12 are used with excessively hard brushes/pads.

Correctly cleaning and maintaining natural stone floor coverings is essential if the stone is to keep its characteristic look over many years. Before cleaning, you must therefore have thorough knowledge of the stone's properties based on its mineral composition and surface treatment, as well as its usage. The wear and dirt on the stone is closely connected to these factors.

Knowing the fundamentals—such as the type of stone and its properties—means that cleaning and maintenance errors can be avoided, as well as their unwelcome consequences (including dullness, stains, and color deviations).

Preventing Damage to Floor Coverings

Natural stones with a low level of hardness, such as marble, are relatively easy to scratch. To protect the flooring in reception lobbies, for example, it makes sense to install a system for catching dirt upstream in order to keep penetration by coarse dirt, such as sand and small stones, as low as possible. This zone should be sufficiently large and should measure between six and eight strides (approximately 15 to 20 feet). When it comes to regular cleaning, it is also sensible to start in the area in front of the building because the majority of dirt in buildings is brought in on foot.

Man cleaning rotating door entryway with karcher compact sweeper

Woman cleaning poolside area with Karcher floor scrubber

Should Natural Stone Be Cleaned Manually or Mechanically?

Depending on the size of the floor to be cleaned and the layout of the space, it becomes more cost-effective to use a commercial floor scrubber rather than manual cleaning methods for areas starting around 1,000 square feet. This is because machines can clean larger footprints in a fraction of the time, significantly increasing staff productivity. Furthermore, separate fresh and dirty water tanks reduce the risk of cross-contamination, protect users from coming into contact with soiled water, and minimize physical strain on the operator. Thanks to precisely adjustable brush contact pressure, the mechanical scrubbing action can be adapted to delicate stone surfaces with great precision. The built-in squeegee system ensures dirty water is vacuumed up instantly, leaving the floor dry and safe to walk on immediately. A floor scrubber featuring cylindrical roller technology is particularly well-suited for textured or cleft natural stone floors, as the roller brushes excel at penetrating grout lines and uneven surfaces to loosen trapped dirt.

Conversely, manual cleaning equipment—such as a wide-area commercial flat-mop system—is ideal for smaller rooms, spaces crowded with furniture, and tight corners. Manual cleaning also provides the best precision when working directly along baseboards and edges.

Maintenance Cleaning of Natural Stone Floor Coverings

Maintenance cleaning is a repetitive task performed at set time intervals, such as on a weekly basis.

There is always the option of wiping and collecting dust, particularly on polished natural stone floors, and this cleaning method is suited to coarse dust removal. However, generally speaking, wet cleaning is predominantly used for natural stone floors.

When performing maintenance cleaning on natural stone floor coverings, you can maintain their original appearance by using appropriate wipe care products or floor shine cleaners. It is important to avoid applying an excessive dose because the traces of wiping may become visible, particularly on sanded or polished floors. This also results in the formation of cleaning detergent residues, which give floor coverings a dull finish. Since the stones may contain metal oxides due to their formation process, there is the risk of rust with excessive wet wiping or if water is on the surface for too long.

Man cleaning indoor area with Karcher floor scrubber

Deep and Intensive Cleaning of Natural Stone

During deep cleaning, stubborn dirt and/or worn protective coatings or other residues that may detract from the look of a surface are removed. Deep cleaning is generally only carried out at longer time intervals.

If a natural stone floor is being relaid, deep cleaning is first required in order to remove any stubborn dirt generated during construction work.

The first step is to remove loose, coarse dirt by sweeping or vacuuming it. Stubborn contaminants, such as varnishes and paints, are removed using a wooden spatula or blade. Dispersion paints can be effortlessly removed using an alkaline deep cleaner. Apply the alkaline deep cleaner in an undiluted form, let it soak for approximately five minutes, and scrub it with a green hand pad. In the case of slate, which is alkali-sensitive, you should only use the mechanical method with a wooden spatula or blade. Gypsum and mortar residues can be removed using a spatula. Since mortar contains silica sand, you must be particularly careful to cause no scratches on highly polished areas.

Cleaning indoor area with Karcher compact floor scrubber

Top down view of 2 Karcher floor polishers in operation

Cement Film Removal

Grouting a natural stone floor covering generally leaves behind a cement film. This film can be removed after thoroughly pre-rinsing the floor covering with an acidic cleaner. You should test the reaction of the floor covering (any changes in color hue) to the acidic cleaner on an inconspicuous area beforehand. Before starting the actual cleaning process, the area to be cleaned should also be pre-wetted with clean water such that the joints are saturated with moisture and not damaged by the acidic cleaner (pH value 0.7).

Particular care must be taken on floor coverings that are highly acid-sensitive, such as marble, limestone, and travertine. For acidic deep cleaning on these surfaces, it is highly recommended to use a floor scrubber with cylindrical roller technology in a single-pass method. The cleaning solution is applied to the floor, the surface is scrubbed, and the dirty water is immediately vacuumed away in the same motion. This ensures that the acidic cleaning solution only makes contact with the natural stone for a few seconds, preventing chemical burns or etching. This rapid process is not possible with a standard single-disc floor buffer because it lacks an integrated vacuum system, leaving the acidic cleaner on the stone for too long before it can be recovered by a wet/dry vacuum.

Grout haze and cement film are safely lifted thanks to the powerful mechanical action of cylindrical roller technology (delivering a contact pressure of 3 pounds per square inch at 1,100 RPM), stripping residue without abrading the stone. For stubborn buildup on smooth or polished areas, heavy-duty green roller pads are recommended. Meanwhile, for cleft or textured surfaces, standard red brushes or orange brushes with varied bristle heights yield the best results.

For acid-resistant natural stone coverings, such as granite, a two-step method can be utilized. The acidic cleaning solution is applied to the floor and allowed a contact time of approximately five minutes while the floor scrubber passes over the area multiple times. The second step engages the vacuum squeegee system to recover the slurry, followed by a thorough rinse with clean water to completely neutralize the surface.

3 Diamond Pads arranged in front of Karcher floor scrubber

Renovation of Lime-Bound Stones

When it comes to restoring calcium-based stones like marble, polishing with diamond abrasive pads has become the industry standard. To restore the stone's original high-gloss finish, a floor buffer or a disc-head floor scrubber should be guided over the surface 10 to 15 times across two or three stages, using diamond pads of progressively finer grits (coarse, medium, and fine). No chemical cleaning agents are required for this process—only clean water. Between each stage, be sure to thoroughly rinse the stone slurry out of the pads.

However, deep cleaning beforehand is recommended in order to safely remove dirt, residues from protective coatings, hard water stains, and cement film.

Reinvigorate Old High-Gloss Finishes with Crystallization

Over time, continual use of polished stone floor coverings like Carrara marble will leave scratches and scuff marks. The gloss finish will be affected, and the floor covering will become unsightly and have a dull finish. At the same time, re-soiling is made easier, and therefore greater cleaning efforts are required. To combat this trend and to reinvigorate the original high-gloss finish, stone crystallization will be required. There are two methods of crystallization to choose from, depending on the required level of surface shine.

The Benefits of Crystallization

Crystallization produces a glossy look, gives the impression of cleanliness, and retains the character of the stone. The surface is also hardened and compacted at a micro level, which is associated with increased resistance. Moreover, the surface remains breathable such that residual moisture can escape.

This results in:

A high-quality surface finish that lasts longer
Reduced re-soiling
Considerably more efficient maintenance cleaning
A consistently high cleaning quality
Greater cost-effectiveness in cleaning and maintenance

Additional Methods for Producing Shiny Natural Stone Floors

Method 1: Producing a High-Gloss Finish Using Single-Disc Machine Technology and Crystallizing Agent Powder

For all high-gloss, calcareous floor coverings, it is recommended that you use high-gloss crystallizing agent powder with a single-disc machine. This treatment method gives the floor covering a "watery sheen," while also increasing its abrasion resistance. The colors and grain are also brought to the fore. In addition, the fact that the floors have been treated makes maintenance cleaning easier. If the floors are correctly maintained, the high-gloss finish will be retained over a long period of time.

Preparation:

The use of a slow-running single-disc machine (180 RPM) in this crystallization process has proven effective. You will also require an additional weight, a pad drive board, crystallization pad, and a spray bottle for wetting the crystallizing agent powder.

Steps:

First, the floor covering must be thoroughly cleaned; that is, the glossy layers, protective coating, and dirt build-up must be removed. This is undertaken according to the method previously outlined. The cleaned floor is then neutralized with clean water and left to dry.
High-gloss crystallizing agent powder is evenly sprinkled (0.95 ounces per 10 square feet) on the thoroughly cleaned and dry floor, and a moderate amount of water is then added using a spray bottle.
The mixture is worked in using the crystallization pad (silver) until it reaches a creamy consistency.
Use the pad to work the crystallization mixture until the material is used up and an even gloss is produced.
Then brush out any remaining material residues—particularly from the grout lines—using a floor buffer equipped with a scrubbing brush and plenty of water, then extract the slurry using a wet/dry vacuum. Use a commercial flat mop for a final damp-wipe if necessary.

The area performance for this method is between 108 and 161 square feet per hour.

Method 2: Satin Finish Using Wax-Free, Genuine Stone Fluorosilicate with Roller Technology

This alternative crystallization method is ideal for applications where a satin or matte finish is preferred and higher area coverage rates are required. The floor covering intended for crystallization must not be sealed or pre-treated. If a coating is present, it must first be stripped via a deep-cleaning process.

Steps:

Cover permanently installed fixtures to protect them from fine dust.
If necessary, perform deep cleaning on the floor covering using the two-step method.
Use a pump sprayer to apply the liquid crystallizing agent onto sections of the dry floor (approximately 0.34 fluid ounces per 10 square feet).
Use a microfiber applicator or a flat mop to spread the crystallizing agent evenly.
Run the floor scrubber equipped with green grit brushes immediately over the treated area.
Slowly pass over the area at full contact pressure multiple times until the desired polish is achieved.
Use soft white brushes to rinse the area with clean water, picking up any fine dust produced during the process.

The area performance for this process is between 1,075 and 3,750 square feet per hour, depending on the floor scrubber's working width, making this crystallization method very efficient and cost-effective.

This method is also particularly well-suited to textured, hewn, and calcareous natural stone floor coverings because the roller brushes themselves penetrate into the grooves and bring about the crystallization effect.

Granite

Granite is a plutonic rock, which is largely composed of feldspar (60%) and quartz (30%), usually white-gray, reddish, and brownish in color, and with black mottling. This type of rock has a fine to coarse-grained structure and is very hard. It is generally laid on floors after it has been sanded and highly polished; however, it has also been increasingly used in hewn form. Granite is resistant to all commonly used cleaning agents.

Slate

This igneous and sedimentary rock is composed of quartz and varying amounts of decomposed feldspar and has a flaky structure. A distinction is drawn between gneiss mica schist and clay slate, with the latter resistant to commonly used cleaners. While strongly acidic cleaning agents may cause stains, strongly alkaline agents make floor coverings "bleed." Slate floor coverings can be treated with shale oil to keep their special character with a dull gloss finish. The oil can be polished out using roller technology and soft polishing brushes.

Marble

Marble is extracted by blasting it out of its natural surroundings in large blocks and is then further processed into the required form. Marble is one of the medium-hard natural stones and is the result of the metamorphism of limestone under the effect of pressure and temperature (metamorphic rock). It has a very dense, fine to coarse-grained structure. Because of the effect of minerals and metal oxides during the formation process, marble can vary in color and structure. Its color spectrum ranges from pure white, such as Carrara marble from Tuscany, to silver, black, red, green, yellow-brown, and violet-blue. Marble, which is well known for its gloss finish, can also be polished and is suitable for outdoor use thanks to its frost resistance. However, it is prioritized for use as an indoor floor material. This type of stone is used in abutting panels, whether in a polished form or with a satin finish, whereby the joints are adjusted according to the color image. Marble is unsuitable for use in kitchens or restroom areas because this type of stone is acid-sensitive due to its lime base. This means that drinks like cola and mineral water, as well as acidic cleaning agents, may cause damage to the material.

Travertine

This freshwater limestone is formed by calcite precipitations from highly calcareous sources. It is therefore composed of virtually 100 percent lime and has a color which varies in intensity from cream colors to yellowish and tan due to iron oxidations. This material also stands out thanks to its vibrant structure with many small pores which are often joined to form chains. It is normally sanded but can come in filled forms and can also be polished or crystallized. This type of material is very sensitive to acids.

Limestone and Fossiliferous Limestone

Close-up view of a Jurassic and Solnhofen limestone surface

These stones are types of sedimentary rock. They are part of the broader limestone family and are inherently soft and highly acid-sensitive. They typically range in color from yellowish-white and cream to charcoal gray or warm tan. This type of material is richly veined and frequently contains highly visible fossil formations. These stone tiles are commercially available in natural cleft, honed, and high-polished finishes.