Many white marble tiles contain naturally occurring deposits of iron. Iron is a mineral found in stone and can occur randomly throughout the stone. If iron is present in the marble tile, it will begin to oxidize when exposed to water or other oxidizers such as acids and household bleach.
It is for this reason that we recommend not using white marble in a shower.
White marble tiles can remain for years without yellowing then over time may slowly turn yellow, and in severe causes, may turn completely brown. This oxidation process is accelerated when the tile is saturated as in the flood in the above example. This process of oxidation is similar to the rusting of metal. If you expose a brand new nail to water and air it will turn brown and rust. The same process is occurring with the iron in the marble. If water and/ or air is eliminated the iron will not oxidize. This is the reason certain white marble suddenly turn yellow.
The process is difficult to reverse and replacement of the tile may be necessary. The following stain removal technique has proved successful in several cases. Before testing this procedure it is important to first determine if iron is the cause.
Testing for Iron:
1. Before assuming the marble is yellowed due to iron, be sure to attempt cleaning and stripping as outlined in the first two possible causes above. If these procedures fail then testing for iron will be necessary.
2. If a flood has occurred or excessive water was used first check the water for iron. If any amount of iron is detected then it is possible iron has entered the stone through the water supply. To eliminate the iron there are chelating chemicals that can be added to the water to prevent the iron from staining. This is very important if the tile is cleaned with this water.
3. Even if the water contains no iron the tile can be checked for iron content. We can remove one tile and have it analyzed for total iron. If there are spare tiles that have never been installed it would be a good idea to also have them tested for total iron. If iron is present naturally in this stone, it will probably be detected in the spare tiles. If the results return with iron present then the following procedure should be tested.
4. We can check the tile for moisture using a moisture meter. If the tile contains water, it is very possible that iron is beginning to oxidize.
The Process for Removing Iron Staining:
1. Prepare a solution of water and the following chemical: Sodium Hydro sulfite and Sodium Metabisulfite. These chemicals are available in a product called Iron-Out® you may have seen at your plumbing supply or home center.
2. We will mix a solution in water and apply to the effected tile, and allow the solution to soak into tile and kept wet for several hours. It is important that the solution not be allowed to dry. After several hours pick up excess solution with a wet vacuum and rinse thoroughly with water and a chelating agent such as EDTA.
3. Be prepared to expect that the marble may need to be repolished since these chemicals can etch marble.
If the above procedure fails we can then prepare a poultice with diatomaceous earth and the Iron Out™. The poultice mixture will be applied to a small area and covered with plastic wrap. After 24 hours remove the poultice paste and rinse the area with water and a chelating agent. If the stain is removed, the entire floor can be treated. If the stain still remains then replacement is the only solution.
NOTE: There are also some new chemicals that are available which contain Ammonium Thioglycolate which look promising for removing iron oxidation.
The yellowing of white marble is a common problem. New installations should be sealed with a good quality penetrating sealer (impregnator) which will help prevent oxidation of the iron by eliminating moisture
Please feel free to contact Brilliant Services at 205-617-6330 to get a FREE quote on whatever type of problem you have with your stone.