Limestone is a natural calcium carbonate (CaCO3), a sedimentary stone with a smooth, granular appearance and varying degrees of hardness. It is highly reactive to acids, so acidic cleaners like citrus cleaners can easily etch or interact with the calcium carbonate in ways that damage the limestone. Limestone tile comes in three basic finishes: honed, semi-polished and highly polished. However, unless it is a hardened grade of limestone, it will never polish to the degree of granites or marbles. Cleaning limestone tile starts with understanding what makes it dirty. Limestone is soft, porous and stains easily, it is also sensitive to hard water. Limestone should be treated with a limestone-specific penetrating sealer to reduce the potential for staining.
Remove all grit and surface dirt using a canister vacuum cleaner. Grit is the primary abrasive that breaks down the sealer on natural tiles. When the sealer breaks down, its protective quality is compromised, allowing stains and marks to occur more quickly. Daily floor cleaning should include using an untreated dust mop as well as mats to trap dirt at entryways.
Scrub your tiles with a pH-neutral stone cleanser that is specifically approved for limestone. Typically, these are sprays, but if you have a large area, there are products that can be mopped on and rinsed off. You will need to dry the floor with towels, as you go, to remove the dirt from your floor. Do not wash limestone with household soap and water. Soaps will build up and make the surface look scummy.
Use your toothbrush to remove stains. Work in a circle from outside to inside, mopping up with a clean rag. If the stain persists, there are special stone and grout cleaners for limestone that may be stronger than the a cleanser or designed for specific stains like oil and grease stains. There are also poultice products available for hard stains. These work by a capillary action and take as much as 48 hours to draw a stain out.
Rinse your scrubbed tiles with soft or distilled water and immediately wipe dry. Do not leave water or fluids to sit on your tiles. Soft drinks, vinegar, fruit juices and wine, as well as many bathroom products, are just some of the liquids that etch and stain limestone.
Consider steaming the tile. Because limestone is porous, even if it is sealed properly there are often indentations or pockets where water and dirt can accumulate. Hard water in small pockets can cause black spots or discoloration. You can often rent steamers from rental companies or home improvement stores. Many steamers come with interchangeable heads and disposable towel attachments. The heat and intensity of the steam, coupled with the moisture and absorption aspects of the towel, should loosen and dissolve many types of soils or stains. Dry your limestone tiles thoroughly after steaming.
Reseal your tile if a water drop, sitting on the tile for five minutes, leaves a dark spot or appears to be absorbed into the tile. Seal your tile using a quality sealer with a good reputation like AquaMix Sealer's Choice Gold. Don't wax your stone floor with the waxes found in most supermarkets. Buy the type of polish or wax product recommended for your tile and sealer.