Marble lends a touch of elegance and luxury to floors, stairs, furniture or even a fireplace mantel. Though this material is known for its beauty and strength, it also features a surprisingly porous surface, leaving it susceptible to stains. While rust and other metal stains can be tough to remove from marble, the Marble Institute of America suggests using an absorbent material, like diatomaceous earth, to draw rust stains out of marble.
Spotting Rust on Marble
Metal stains on marble leave an orange or brown mark that typically takes the shape of the object leaving the stain. These stains are caused by proximity or contact to a variety of metals, though common culprits include chairs, screws or fasteners, cans or flower pots. While deep-seated rust stains on marble may be permanent, according to the Marble Institute of America, it may be possible to remove these stains using an absorbent material to draw the rust out of the marble.
To remove rust stains from marble, you must create a poultice using a white absorbent material, such as diatomaceous earth. When mixed with a commercial rust remover and left on the marble, the drying properties of the earth help to draw the rust out of the marble so it can be scraped away easily when the poultice is removed. Diatomaceous earth, which can be found at pool and garden supply stores, consists of tiny fossils or skeletons from underwater plants. This material can have sharp edges, so wear gloves to protect you hands when handling diatomaceous earth. A dust mask can help you avoid breathing dust from the earth as you work.
Preparing the Poultice
To prepare a poultice for marble, you'll need roughly 1 pound of diatomaceous earth for every square foot of stained marble. Put the earth into a container and add a liquid commercial rust remover to the container, blending the two together until the mixture takes on the consistency of peanut butter. The amount of rust remover you'll need to add varies depending on the type of remover you use, so use texture and consistency as your guide rather than ounces.
Applying the Poultice
After you've mixed your poultice, use a wooden or plastic spoon to apply a 1/4- to 1/2-inch-thick coat across the stained area. Extend the poultice about 1 inch on every side of the stain to cover the unstained marble surrounding the stain. Cover with plastic wrap, then use tape to secure the plastic to the marble. After 24 hours, remove the plastic, but don't disturb the poultice until 48 hours have passed. Next, scrape away the poultice and use distilled water to rinse the marble, then buff it dry with a clean, soft cloth. Examine the marble to see if the poultice worked. You can repeat this process up to five times to remove additional rust.