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Knowing the basics of stain removal will help end users enjoy their finished stone installation over the long term
Black Magic marker on a white marble floor. Tar tracked on your granite floor from construction crews. Rust stains appearing in your limestone
shower. Mysterious yellow spots appearing all over your marble countertop. These are just a few of the countless varieties of actions which can
result in the staining of marble, granite and other stone surfaces. Is the stone ruined? Does it need to be replaced? The answer may be “yes”
unless you know the techniques that will remove most imbedded stains from stone. Marble and other natural stones are porous materials.
This porosity is why they stain so easily. It is also why stains can be removed. In many cases, a stain can be removed simply by reversing the
staining process. In other words, since the stone has literally absorbed the stain, we can re-absorb the stain into a different material. This
different material is referred to as a “poultice,” and it can be made with powdered whiting (sold in most paint stores) and hydrogen peroxide
or a chemical reducing agent, depending on the nature of the stain. The poultice should be made and applied as described for removal of
each particular stain.
- Poultice application materials
- Cotton balls
- Paper towels
- Gauze pads
- Poulticing powders
- Clays (Attapulgite, Kaolin, Fullers earth)
- Talc
- Chalk (whiting)
- Sepiolite (hydrous magnesium silicate)
- Diatomaceous Earth
- Methyl Cellulose
Clays and diatomaceous earth are usually the best. Do not use whiting or iron type clays, such as Fullers Earth, with acidic chemicals. They will
react with the material, canceling the effect of the poultice.
Most stains can be classified into one of the following categories:
1. Oil-based stains
grease, tar, cooking oil and food
2. Organic stains
coffee, tea, fruit, tobacco, cosmetics, etc.
3. Metal stains
iron (rust), copper, bronze, etc.
4. Biological stains
algae, mildew, lichens, etc.
5. Ink stains
magic marker, pen, ink, etc.
There are, of course, other materials that will cause staining, but these five categories are the most common.
Applying the poultice
Once the stain is identified, the following steps can be followed:
1. Wet the stained area with distilled water. Pre-wetting fills the pores of the stone with water, isolating the stain and accelerating the removal
by the chemical.
2. Prepare the poultice. If a powder is to be used, pre-mix the powder and the chemical of choice into a thick paste, the consistency of peanut
butter. In other words, wet it enough so that it does not run. If a paper poultice is to be used, soak the paper in the chemical. Lift the paper
out of the chemical until it stops dripping.
3. Apply the poultice to the stain, being careful not to spill any on the non-stained areas. Apply the poultice approximately 1⁄4 inch thick,
overlapping the stain area by about 1 inch.
4. Cover the poultice with plastic (food wrap works well), and tape the plastic down to seal the edges.
5. Allow the poultice to dry thoroughly. This is a very important step. The drying of the poultice is what pulls the stain from the stone into the
poultice material. If the poultice is not allowed to dry, the stain may not be removed. Drying usually takes from 24 to 48 hours.
6. Remove the poultice from the stain. Rinse with distilled water and buff dry with a soft cloth. If the stain is not removed, apply the poultice
again. It may take up to five applications for difficult stains.
7. Some chemicals may etch the marble surface. If this occurs, then apply polishing powder and buff with a piece of burlap to restore the
shine.
Many stains are so deeply imbedded that the poultice alone will not be completely effective. Some type of chemical solution will need to be
added to the poultice to dilute and/or react with the stain. The process is rather simple. When the poultice and chemical are applied, the
chemical is absorbed into the stone. The chemical reacts with the stain and is re-absorbed into the powder/material.
Stain removing chemicals
How do you choose the proper chemical for a given stain? First, you need to identify the stain. This is the most important step in stain
removal. If you know what caused the stain, then you can easily look at a stain removal chart for the proper chemical to apply. If the stain is
unknown, then you need to play detective. Try to determine what caused the stain. If the stain is near a plant container, it might be that the
plant was over-watered and the soil has leached iron onto the stone. The color of the stain may help to identify the cause. Brownish stains
may be iron (rust) stains. The shape or the pattern of the stain may be helpful. Small droplet-sized spots leading from the coffee pot to
someone’s desk are a sure giveaway. Do some investigating and use your powers of observation. This will almost always lead to the
identification of the cause of the stain.
If, after thorough investigation, you still have no idea what the stain is, then you will need to perform a patch test. A patch test simply means
applying several chemical poultices to determine which will remove the stain.