Frederick M. Hueston, Technical Editor
"Help, I spilled cooking oil all over my new granite countertop
and it left a huge stain." How do I remove the yellow stains
from my white marble shower?" Can the stains on my floor be
removed or do I need to replace the floor?"
are just a few of the countless questions fabricators, restoration
contractors and others in the industry get on a daily basis. Is
the stone mined? Does it need to be replaced? The answer may be
"yes"-unless you have the magic potion that will remove
most imbedded stains from stone.
"Guide to Stain Removal" which appears as part of this
article and a few simple techniques are what I consider to be the
granite and natural stone are porous materials. This porosity is
why it stains so easily. It is also why stains can be removed. All
that's needed to remove a stain is to reverse the staining process.
In other words, the stone has literally absorbed the stain and we
simply re-absorb it into a different material. This different material
is what we call a poultice. A poultice can be made with powdered
whiting and hydrogen peroxide or a chemical reducing agent-depending
on the nature of the stain. Whiting is sold in most paint stores.
The poultice should be made and applied as described for removal
of each particular stain.
have found that most stains can be classified into one of the following
Oil-Based Stains: Grease, tar, cooking oil and food stains.
Organic Stains: Coffee, tea, fruit, tobacco, cosmetics, etc.
Metal Stains: Iron (rust), copper, bronze, etc.
Biological Stains: Algae, mildew, lichens, etc.
Ink Stains: Magic marker, pen, ink, etc.
are, of course, other materials that will cause staining. but these
five categories are the most common.
the stain is identified, the following steps can be followed:
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.
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 politice is to be used, soak the paper in the chemical.
Lift the paper out of the chemical until it stops dripping.
Apply the poultice to the stain being careful not to spill any on
the non stained areas. Apply approximately 1/4-inch thick over-lapping
the stain area by about one inch.
Cover the poultice with plastic (food wrap works great). Tape the
plastic down to seal the edges. It also helps to poke several small
holes in the plastic. so that the powder will dry out. Failure to
do this may result in the poltice staying wet.
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
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
Some chemicals may etch marble and limestone surfaces. If this occurs,
then apply polishing powder and buff with a piece of burlap to restore
(Attapulgite, Kaolin, Fullers earth)
Sepiolite (hydrous magnesium silicate)
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.
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 poulice. 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.
do you choose the proper chemical for a given stain?
you need to identify the stain. This is the most important step
in stain removal. If you know what caused the stain, 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 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 color stains may be iron (rust) stains. The shape
or the pattern of the stain may be helpful. Small droplet size spots
leading from the coffeepot 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.
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.
are also pre-prepared poltice mixes that have the chemicals already
added. All you have to do is add water.
way to reduce the amount of staining on any stone surface is to
make sure it is sealed with a good penetrating sealer or impregnator.
Iron (rust) - Poultice with Oxalic Acid + Powder + Water. May also
try a product called Iron-Out (available at hardware stores). Both
mixtures may etch polished marble, so re polishing will be necessary.
Ink - Poultice with Mineral Spirits or Methylene Chloride +Powder.
Oil - Poultice with Ammonia+ Powder Methylene Chloride can also
be used on tough oil stains.
Coffee, Tea & Food - Poultice with 20 percent Hydrogen Peroxide
Copper - Poultice with Ammonium Chloride + Powder
Paint (water-based) - poultice with a commercial paint remover +
Paint (oil) Poultice with Mineral Spirits + Powder. Deep stains
may require Methylene Chloride.
use extra caution when handling all chemicals listed above. Thoroughly
read Material Safety Data Sheets for each chemical before use.
published in August 12, 2001 issue of STONE magazine. This article
appears by permission of the author.