Ask the Experts – March 2016
I have a question regarding polished porcelain mosaic tiles. Polished porcelain is becoming more popular these days with so many “marble” looks being manufactured. I have a client wanting to use a polished porcelain for her shower walls and would like to use the coordinating polished porcelain 1.5” x 2.5” basket weave mosaic for the shower floor (it is not available in matte). Is it ok to use any polished porcelain mosaic on a shower floor? Please advise.
Small mosaics generally do not pose a slip/fall hazard in wet areas, even if they are polished. The grout joints are so closely spaced that they create a type of textured surface that lends good traction, even in wet areas with lots of water on the surface. Mosaics have traditionally been used in shower floors with high success and little risk of liability.
– Michael Whistler
Our company has been asked to look at a marble floor that is staining and “rusting.” This has only started happening within the last year or two of the floor’s 15-20 year life. There seems to be no etching or loss of sheen (which does not rule out chemical absorption, I am aware). We have been assured that the cleaning process/chemicals have not changed. The floor is on concrete, with occupied space below, and no evidence of moisture-related damage in that area’s ceiling. Before tearing out this floor and replacing it, I would like to be able to suggest what may be the cause and possible solution prior to going in and having unforeseen issues. Any assistance would be greatly appreciated.
White marble tiles can contain deposits of iron. As a mineral, iron oxidizes and turns the marble yellow or brownish red when exposed to water or acids, similar to the way metal rusts. It is possible for the oxidation process to occur many years after the tile was installed. The rusting of the tile may have been initiated or accelerated if the tile installation has recently been exposed to a large amount of water or if the chemistry of the wash water has changed.
It is possible to check the water supply for iron. A plumbing supply store should be able to provide a test kit. If iron is detected, the water supply can be chemically treated to remove the iron.
The tile itself can be tested for iron content. A yellowed tile can be removed from the installation and sent to a lab for testing. If there is attic stock tile that has never been installed, it can also be tested. Comparing the test results of the tiles will help determine whether the iron content was native to the tile or introduced through the water supply.
The rusting process is a chemical change internal to the tile and is difficult or impossible to reverse. It may be possible to remove the stain by applying a poultice consisting of a thick plaster of a product called Iron Out, which contains sodium sulfites. Test a small area by applying the paste and keep it damp for several hours. Remove the solution with a wet vac and clean water. Make sure your wash water does not contain iron. If the stain is removed, the entire floor can be treated in this manner. The process will cause some etching and the surface will likely have to be re-polished.
If you determine iron oxidation is not the cause, you may discover the cleaning agents or the cleaning procedure has changed (such as using the same mop and wash water on the marble after being used in a dirty environment). Marble is porous and has naturally occurring pinholes. After years of wear, the surface of the marble may have become less polished and more open to absorption of dirt. Normal traffic or a dirty mop could be introducing dirt into the pinholes.
After you have ruled out iron mineral staining and suspect cleaning is the cause, it is possible to clean the marble with an alkaline solution. Test the alkaline cleaning solution on a small area before attempting the entire floor. The cleaning process will require scrubbing, which will likely dull the surface. The surface can be re-polished.
The size and scope of the project may determine the best course of action. Ultimately, removal and replacement may be the solution.
I will be interested to know what you discover in your investigation and the approach you take to correct the issue.
– Mark Heinlein