Why does my Marble Floor have Orange Rust Stains and How can I remove them?


My client's shower has a pebble marble floor that was recently installed and some of the marble pebbles are developing rust stains around them. These just appeared after installation, they were down just two weeks and it started (still continuing, expanding). The pan is new, hot mopped, mortar bed still getting information on the grout and adhesive.

My research shows that iron is commonly present in dolomite: "Ferrous iron commonly substitutes for some of the magnesium in dolomite, and a complete series very likely extends between dolomite and ankerite [∼CaFe(CO3)2]. Manganese also substitutes for magnesium, but typically only to the extent of a few percent and in most cases only along with iron.”

My real question is about responsibility. Is the retailer selling this product responsible? One would think the stone supplier would have verified the material for iron content to sell it this way (pebbles are in shower floors around the world). Obviously, the supply chain is likely quite complex and the extraction company may have no idea they had hit a streak of iron. The retailer is not smart enough to know anything other than how to charge back the seller.

As you might guess, I’m leaning heavily that the retailer needs to right this wrong, and get the customer off the hook. Any thoughts?


Well… I assume when you say dolomite you are referring to a type of marble, that might in fact be a type of limestone that is commercially referred to as a marble.  I assume you have substantiated that it is in fact a predominately a dolomite marble versus a calcite marble.

Either way, both types of marble are known to contain the mineral iron sulfide (pyrite) that can develop undesirable orange-like rust stains.   It is naturally occurring.   Some stones may have more or less than others.  There is no standard that says how much it can contain.

Often the problem is that the stone is being subjected to excessive moisture.   Obviously a shower used daily stays wet.  If the weep holes of the drain at the hot mop were not protected it could cause the mortar bed to retain excessive moisture.   If they had applied a liquid applied waterproof membrane on the mortar bed they would have limited how much moisture the marble would be subjected to as the moisture would dry fairly rapidly.  That may or may not have prevented the staining.

Assuming their mortar bed isn’t being subjected to excessive moisture they could to after the retailer who can go after the importer who can go after the supplier…   Considering the cost is substantial to replace the shower floor that might not go far.

There are stone rust removers at Home Depot and poultices they can try to remove it.  They then could seal the floor to see if that will prevent the stain from reoccurring, but they have to reapply regularly.  Prosoco has sealers that are suppose to last longer as they penetrate block the pores of the stone, but marble is very dense so don’t know how well it will work.

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