STAINS COME FROM MANY SOURCES BUT MOST ARE REMOVABLE
The key to success is cleaning up any spills and treating any resulting stains as soon as you can. Understanding the source of the stain will help in determining the best treatment. Many options are available for treating stains on natural stone from creating your own poultice to using convenient ready-made poultices. Ask us for help if you need it.
WE ALL KNOW WHAT A STAIN IS.... OR DO WE?
Let's start by saying that a stain is a discoloration. So far, so good. The fact is, however, that not all discolorations are stains. To illustrate the point, let's take, for example, a piece of common fabric. Fabric is typically absorbent. Therefore, if we spill some liquid onto it, the material will absorb it. If it is only water, it will leave a temporary stain. In fact, once it dries the fabric will go back to its original color, but if coffee or cooking oil is spilled on it a stain will occur because the fabric will absorb the staining agent and change its color in a permanent way —unless we do something to remove the agent from the fabric.
On the other hand, if bleach is spilled on that same fabric a discoloration will occur, but it can hardly be defined as a stain because it is actually a permanent damage to the dye that originally made the color of the fabric.
As with the fabric example, when it comes to natural stone there are stains that are true stains and there are "stains" that are actually discolorations caused by something else.
A true stain is always darker than the stained material. If it appears as a lighter color it is not a stain, but either a mark of corrosion (etching) made by an acid, or a caustic mark (bleaching) made by a strong base (alkali). In other words, a lighter color "stain" is always surface damage and has no relation whatsoever with the absorbency rate of the damaged material-stone or otherwise. There is not a single exception to this rule.
A stain is a discoloration of the stone produced by a staining agent that was actually absorbed by the stone. Other "discolorations" have nothing to do with the porosity (absorbency) of the stone, but rather are a result of damage to the stone surface. All those "stains" that look like "water spots" or "water rings" are actually marks of corrosion (etches) created by some chemically active liquid (mostly-but not necessarily limited to-acids), which had a chance to come in contact with the stone. All calcite-based stones such as marble, limestone, onyx, travertine, etc., are sensitive to acids. Therefore, they will etch readily (within a few seconds). Many slates will also etch and so will a few "granites" (those that instead of being a 100% silicate rock are mixed with a certain percentage of calcite).
All stones are, more or less, absorbent. One may say that diamonds or gemstones are not absorbent. That's right, but a gemstone is not actually a stone. It is actually made of one crystal of one single mineral.
All other (less noble) stones are the composition of many crystals, either of the same mineral, or of different minerals bonded together. The "space" in between these molecules of minerals is mostly what determines the porosity of a stone. The porosity of stone varies greatly, and so does, of course, their absorbency. Some of them are extremely dense, therefore their porosity is minimal. What this translates into is the fact that the absorbency of such types of stone is so marginal that-by all practical intents and purposes-it can be considered irrelevant. Some other stones present a medium porosity, and others at the very end of the spectrum are extremely porous. Because of their inherent porosity, many stones will absorb liquids, and if such liquids are staining agents a true stain will occur. Now let's discuss how to remove stains!
HOW TO REMOVE A STAIN
A poultice is the best way to break down and draw out a stain on stone or other hard porous surfaces.
WHAT IS A POULTICE?
A poultice is the combination of a very absorbent medium (it must be more absorbent than the stone) mixed with a chemical, which is to be selected in accordance with the type of stain to be removed. The concept is to re-absorb the stain out of the stone. The chemical will attack the stain inside the stone, and the absorbent agent will pull them both out together. The absorbent agent can be the same all the time, regardless of the nature of the stain to be removed, but the chemical will be different in accordance with the nature of the staining agent since it will have to interact with it. The absorbent part of a poultice could be (in order of preference): talcum powder (baby powder), paper towel or diatomaceous earth (the white stuff inside your swimming pool filter) for larger projects. NOTE: There are convenient poulticing kits that make the task of stain removal easier. You may want to ask your stone care PRO for some specific recommendations.
As we said before, the chemical must be selected in accordance with the nature of the staining agent.
5 CLASSIFICATIONS OF STAINS
1. Organic stains (i.e. coffee, tea, coloring agents of dark sodas and other drinks, gravy, mustard, etc.)
2. Inorganic stains (i.e. ink, color dies, dirt-water spilling over from flower or plant pots, etc.)
3. Oily stains (i.e. any type of vegetable oil, certain mineral oils-motor oil, butter, margarine, melted animal fat, etc.)
4. Biological stains (i.e. mildew, mold, etc.)
5. Metal stains (i.e. rust, copper, etc.)
The chemical of choice for both organic and inorganic stains is hydrogen peroxide (30/40 volume, the clear type-available at your local beauty salon. The one from the drugstore is too weak, at 3.5 volume).
Sometimes, in the case of ink stains, denatured alcohol (or rubbing alcohol) may turn out to be more effective.
For oily stains, our favorite is acetone, which is available at any hardware or paint store. (Forget your nail polish remover. Some of them contain other chemicals, and others contain no acetone whatsoever.)
For biological stains, one can try using regular household bleach or a mildew stain remover designated safe for stone.
For metal/rust stains, our favorite is a white powder (to be dissolved in water) called Iron-out™, which can be found in any hardware store.
How to Create and Apply a Poultice
STEPS FOR CREATING AND APPLYING A POULTICE
1. Identify the stain.
2. Clean the stained area to remove excess from the surface.
3. 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.
4. 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. 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.
5. Apply the poultice to the stain, being careful not to spill any on the un-stained areas. Apply poultice approximately one-quarter-inch thick, overlapping the stain area by about one inch.
6. Cover the poultice with plastic (food wrap works very well). Tape the plastic down to seal the edges. 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.
7. After 24 to 48 hours, remove the plastic.
8. 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 five applications or more for difficult stains.
9. Some chemicals may etch the marble surface. If this occurs, apply a polishing powder and buff to restore the shine.
For further assistance, contact your SurpHaces PRO Partner.