How to remove REALLY difficult stains from porcelain tiles.

Recently we received a tricky complaint from a customer. The plain grey colour porcelain tiles we supplied had been installed in a commercial store where mobile display racks on soft black rubber castors were used. Small greasy looking stain marks had developed under the castor wheels and cleaning staff had been unable to remove them. Stains appeared two days after the castor was put in place on a test tile with a load.

Below you can see two stains that we reproduced using the same castors and the same tiles. 

We did some research and contacted a local company TFC. Tile and Floor Care is a retail supply company that focuses on providing the retail market with high quality floor & tile cleaning products.

At first they recommended TFC Purge which is a specially formulated liquid paste designed to purge dirt and spots from polished porcelain floors. Purge has the ability to release stubborn dirt such as rubber mallet marks, pencil marks and scuff marks from the minute capillaries in polished porcelain. Purge must be used to spot clean before the general clean that is necessary as preparation for sealing. Purge may also be used to remove tough wax coatings that are applied to some polished porcelain during manufacture. Purge is safe and easy to use. Purge is used as is without dilution.

We thought this would do the trick, especially given the reference to rubber mallet marks but... nope. The stains remained even after a post purge cleaning with...

TFC Easy Clean is a powerful alkaline degreaser and neutraliser. Easy Clean must be diluted as instructed for general cleaning purposes. Easy Clean is specially formulated to cost effectively clean floor and tile surfaces that have been soiled with oils, greases and general grime. Easy Clean is free from ammonia and phosphates and is non-abrasive. Easy Clean is also used to neutralise tile and floor surfaces after they have been washed with acids. Easy clean is diluted according to how heavy the dirt is from 1:20 for general cleaning to 1:5 for very heavy grease.

We asked TFC for further recommendations and they suggested...

Sealer Stripper. This product is a very powerful solvent based stripper designed to remove most types of sealers and paints from the floor, including linseed oil and urethanes. Sealer stripper is used undiluted and left on the floor for five minutes before being wiped off and rinsed with water. It is toxic so should be used with care. We poured a teaspoon of the liquid onto each of the stains and left it for 5-10 minutes.

Success! When the tile was cleaned off and dried there was no evidence of the marks. We then cleaned the tiles again with EasyClean.

The U.S. Government Services Administration (GSA) is responsible for inter alia, the maintenance of government buildings. They recommend as policyusing Sodium Carbonate (Na2CO3) an acid or Sodium Hydroxide (NaOH) an alkali (caustic soda) for cleaning stubborn stains on tiles.

As always with difficult stains test a small unobtrusive area with a new product before applying to the entire floor.