Maintaining Natural Stones

Contract cleaners are confronted time and again with the challenge of cleaning floors efficiently and effectively without damaging or discoloring the floor covering. Highly polished natural stone flooring in particular can get damaged if not treated correctly leading to dullness, stains or discoloration. Right methods of cleaning help maintain the natural stone floors.

Initial Cleaning

For the initial cleaning of sanded, polished, hewn or structured natural stone flooring, coarse dirt must be removed as a first step by sweeping or vacuuming.

Stubborn stains, for example, paint can be removed with a wooden spatula or blade. Emulsion paints can easily be removed by applying undiluted alkaline-based cleaning agent, leaving it to act for about five minutes and then scrubbing it out with a green hand pad. For slate which is alkaline sensitive, only the mechanical method with a wooden spatula or blade should be used. Plaster or mortar residues can be removed with a spatula. As mortar contains quartz sand, it is particularly important to ensure that no scratches occur on the highly polished surfaces.

By grouting the natural stone covering, a cement residue is normally left behind, which is removed after a thorough pre-wash of the floor covering with an acidic cleaner (Floor Precleaner, acidic RM 751). The reaction (change of colour) should be tested first with the acidic cleaning agent. Particular care should be taken with acid-sensitive floor coverings, such as marble, Jura, Solnhofer stone or travertine – according to the textbook, the use of acidic cleaners is even prohibited. However, for acidic deep cleaning, the compact scrubber drier using the one-step method has shown to be reliable, due to the strong mechanical action and short contact time of the acidic cleaning agent with the floor.

Green roller pads can be used on smooth/polished surfaces and red standard or orange high/low brushes on hewn/structured surfaces.

Note: Before the acidic cleaning agent is used, the surface to be cleaned must be wetted with clear water, so that the joints are wet and not damaged by the acidic cleaning agent (pH0.7).

The one-step method involves applying the acidic cleaning agent (max. 5%) and working it in with the roller pads or roller brushes and after a few seconds removing the dirty water via the suction lips. The cement residue is removed effortlessly by the mechanical action of the roller technology (contact pressure: 210 g/cm², 1100 rpm), without any negative impact on the flooring. In extremely stubborn cases, the procedure must be repeated several times. This should not be carried out using the single-disc machine, as there is a risk of chemical burn, until the acidic dirty water is picked up again with the wet vacuum cleaner. With acid resistant flooring such as granite, the basic cleaning agent (RM 751) acts within about five minutes. During the contact time, the surface must be cleaned repeatedly with a scrubber drier crosswise. The dirty water can subsequently be vacuumed (two-step method). The surface is finally rinsed with clear water until the acid has been neutralised.

The original appearance of natural stone flooring is retained by maintenance cleaning using suitable wiper care products (e.g. Wiper Care Extra RM 780 (0.5 – 3%) or Floor Shine Cleaner RM 755 ASF. Over dosage must be avoided, as this can cause streaks on sanded or polished surfaces. This can also cause a build-up of cleaning agent layers and give the surface a dull appearance. For smaller, hard-to-reach areas, the use of a twin-chamber wet mop bucket with mop or a suitable scrubber drier for this area size (BR 30/4 C Adv) is recommended.

A scrubber drier with roller technology is the best solution for use on hewn/structured natural stone flooring, as mops have the disadvantage of not gliding easily over wet surfaces and cleaning textiles are subject to rapid wear.

In addition, the roller brush efficiently cleans the surface structure and reaches into crevices to effectively dislodge stubborn dirt. Slate flooring can also be treated with slate oil to retain the special character of its matt sheen. The oil can be polished out with roller technology and suitably soft polishing brushes. Depending on the size and height of the surfaces to be cleaned, the use of machines is more economical already from 100sqm and more thorough than manual cleaning.

Granite

This is a plutonic rock that mostly consists of feldspar (60%) and quartz (30%), with mostly white-grey, reddish and brownish colouring as well as flecks of black. The stone has a fine to coarse-grained structure and is very hard. It is normally laid sanded and highly polished – and recently also more widely in hewn form. Granite is resistant to all conventional cleaning agents.

Slate

This igneous and sedimentary rock consists of quartz and more or less decomposed feldspar with a scaly/flaky structure. One distinguishes between gneiss mica or clay slate, the latter being resistant to conventional cleaning agents. Highly acidic cleaning agents can lead to the formation of stains. However, strong alkaline agents can cause the material to “bleed”.

Gerd Heidrich
Training Instructor
Alfred Kärcher-Vertriebs GmbH

Niels W. Buhrke
Freelance Journalist