For Stone, Concrete and Other Hard Porous Surfaces



Removing stains from stone, tile and concrete surfaces can be somewhat tricky. You will need to evaluate each stain and make a determination as to whether an attempt should be made or if it should be left alone. This guide will provide the information and knowledge you will need to make this determination.

Before we can remove any stain let us take a look at why stone, tile and concrete stains. The why is fairly straight forward—it stains because it is porous. The porous nature of stone, tile and concrete allows fluids to enter and become imbedded below the surface. The size of the pores determine what can enter and become imbedded. Some materials are more porous than others. Honed and textured surfaces are usually more porous than polished surfaces and will have a tendency to absorb more of the staining substance. The longer the stain remains the deeper it penetrates and the more permanent the stain becomes.

Certain chemical reactions can also take place permanently setting the stain. This is one reason why it is important to remove a stain as soon as it occurs. How we remove the stain is to reverse the staining process. In other words, we need something that is more absorbent than the material that is stained. We can literally suck the stain back out and into the more absorbent material. This porous material is what we call a poultice.

The art of stain removal involves first identifying the type stain, then choosing the proper chemical or reagents to be added to a medium to create a poultice, then applying it to the stain to break it down and draw it out. This sounds simple enough but sometimes certain stains can be very difficult.

There are many factors that determine if a stain can be removed. Let's take a closer look at these parameters:


Certain stains are very difficult to remove because of their chemical nature. If you have ever tried to remove magic marker ink from a shirt or blouse you know how hard that can be. On the other hand, certain food stains, although they may look bad usually are fairly easy to remove. In this guide we will take a look at how we classify certain stains and compare that to the difficulty it takes to remove them.


This will impact what it will take to remove it. The following story illustrates this point. I received a call one afternoon from a homeowner who was quite upset with her remodeler. Apparently the remodeler had used a black permanent marker on a white marble floor to mark where he was going to place a wall. When the wall was finally constructed it was decided to move the wall approximately two inches back from the marked area. This of course left a long black line parallel to the wall.

When I asked the customer how long the mark had been there she told me approximately 30 days. The remodeler, who was also present, told me he did not understand why the marker would not come off. He said he first tested the marker by placing a mark on the floor and immediately wiping it off. What the remodeler failed to realize is that the ink from the marker slowly penetrated into the stone. I knew right away that this was going to be a difficult task, but I was still successful at removing the marker. It took several applications, but it worked. If at all possible, try to determine how long the stain has been there. This will give you a good indication on how difficult it will be to remove.


How much of the stone, tile or concrete is stained? This will have a major influence on how long it will take to remove. A small area that has been stained with a few drops of oil is going to take a lot less time than an area that has had several gallons of oil spilled on it. It is important to get a general idea, if possible, of how much of the stain has penetrated. I have several examples where there was so much material spilled on the floor that it soaked all the way through and into the setting bed below. In these cases, it is always nearly impossible to remove the stain entirely.


While this may sound quite obvious, the improper selection of reagents and poultice can make a stain worse or even permanently stained. Rust or iron is probably one of the most difficult stains to remove. It is important to know what reagent to use on iron stains. The wrong reagent can oxidize iron to rust and cause permanent staining. One chemical that will rapidly oxidize iron to rust is common household bleach. I have seen numerous examples where bleach was used in an attempt to remove a rust stain, and it only made matters worse. The stain became darker and larger and was permanently set. The instructions and choice of reagents in this kit have been designed to eliminate the improper selection.


Before any stain can be removed it is extremely important to identify what the stain is. There are several reasons for proper identification. If the stain is unknown and you try to remove it, you may be using chemicals that may not work or even worse, may actually set the stain and make it permanent.

So, how do you identify stains? The first task is to determine if it is a stain. While this may sound like common sense, there are many problems that may look like stains but are not. For example, almost all polished marble will become discolored and dull when it comes in contact with acids. Acids can be found in orange juice, lemons, soft drinks, foods, household and commercial cleaners, bathroom cleaners, and the list goes on and on. This dulling effect caused by acids is called etching.



Etching is not a stain. The surface actually becomes damaged when an acid comes in contact with marble. This is also true of highly polished concrete and some tile surfaces. To remove an etch from marble, refinishing and repolishing are required. Etching is a common problem with marble, especially marble countertops. Etching is commonly confused with staining but, it cannot be removed by stain removal techniques or chemicals.


Another common problem mistaken for staining is the deposits of water spots and water rings. These are the rings left behind from a glass. These rings appear on marble, tables and counter tops almost everywhere and are caused by slightly acidic liquids running down the sides of the glass and etching the marble. They can also be caused by chemicals in the liquid that deposit minerals on the stone. These are sometimes referred to as hard water spots. If the liquid contains calcium or other minerals, it may leave a spot on the surface in shape of the glass bottom. These mineral deposits are the same type that appear in an automatic dishwasher or a glass shower door. These rings and spots are not stains and cannot be removed with stain-removing chemicals and poultices. Again, refinishing and re-polishing will probably be necessary.


Efflorescence is another condition found that is not considered a stain. Efflorescence appears as a white powdery dust on the surface of the material. If you wipe your hand across the surface you will pick up a light powdery residue. Efflorescence is simply a deposit of minerals on the surface. These minerals usually come from the setting bed or from the stone or concrete itself. When it becomes wet during installation or afterward, the water dissolves some of the minerals in the setting bed and carries them to the surface. When the water evaporates the minerals are left behind in the form of a powder.


Stun marks appear on certain marbles as white marks, but cannot be felt if you run your finger across the mark. It seems as though it is below the surface. These stun marks are usually caused by an impact on the surface of the stone such as someone dropping a heavy object or a woman walking across the floor with high heels. These marks occur from an explosion of the crystals in certain marbles. This is very similar to glass when it shatters. These marks can be very deep, extending all the way through the marble. They are very difficult to remove, but again, they are not considered stains.


When stone, tile, and concrete become wet, they have a tendency to darken. This is especially true when newly installed. The setting bed is usually very wet. The water migrates to the surface to escape and evaporates. This drying process can take a very long time, depending on the temperature, humidity and air flow. Certain granites can take months to dry.

Moisture can appear uniform throughout the entire surface, or it can appear blotchy. The best way to determine if you are dealing with wet material is to use a moisture meter. These meters are inexpensive (about $250.00) and can help detect many problems related to moisture. As an alternative to using a moisture meter, take a heat gun or hair dryer to the suspected wet area and see if the area lightens.

Caution: Do not apply too much heat, especially to granite, because it may cause the crystals in the stone to expand and spall or the stone to crack.


It is also possible to run into combinations of conditions, such as a stain and an etch. Spilled wine can result in this condition. The tannin in wine will stain, and the acid may leave an etch. In this case, it is necessary to first remove the stain and then refinish or repolish the etch.


How can you tell if you are dealing with a stain or an etch or something else? This is difficult unless you are very familiar with all these conditions. This is where it is necessary to become a detective. Of course, if it was you who spilled something, you will know what it was. Usually, if you are the contractor and are called in to look at a stain, you may not be so lucky as to know what caused the stain. The following steps comprise my investigative process for determining what it is that caused the stain, if in fact it is a stain.

1. Ask the customer.

Do not play the “know-it all-expert.” Ask what the stain is. Chances are the customer who called you to remove the stain knows what was spilled there. Knowing the identity of the stain is half the battle. Once the stain is identified a proper reagent can be chosen to remove it.

2. Detective work.

What if the stain is not known? This is where you need to become a detective and start your investigation. Why is this so important? Why not apply several different reagents and choose which one works? This might make some sense except for one problem. Certain stains will become permanently set with the use of certain reagents. For example, iron oxidizes when exposed to bleach and acids. If clay poultices are mixed with acids, it can turn brown or yellow. This is cause by the iron in these clays becoming oxidized by the acids. So, it is extremely important to identify the stain as well as possible.

3. The investigation.

Next, determine if it is a stain. If an acidic substance came into contact with marble, for example, it is going to etch. Etching can range from mild to severe. If the spot is dull, clouded, or whitish, it may be an etch. Feel the spot. If it is not as smooth as the surrounding surface, you can be sure it is etched. This is not to say that if it is smooth it is not etched. A mild etch can still feel smooth. The simplest way to determine if a marble surface is mildly etched is to place some polishing powder on the etch, take a white pad with a little bit of water and work the powder into a creamy slurry, rubbing the slurry across the spot for several minutes. If it is an etch this process is likely to remove it or improve it. If the etch is deep this simple technique will not work very well. You will need to re-hone the area before you can polish it. You must determine that you're dealing with a stain and not an etch, a wet stone, stun mark, or other type of discoloration that is not caused by a staining agent.

To further investigate take a look around. Where is the stain? Is it near the stove or refrigerator? This is a good indication that it may have been caused by food or cooking oils. Is there a certain pattern to the stain? Does it appear as a splash? This would indicate that something liquid was dropped. Does it appear smudged? This would indicate something more solid was dropped. What color is the stain? If it's red, near the refrigerator, it could be ketchup, a fruit drink, strawberries, etc.

Use some common sense and try to determine how the stain may have gotten there.


Determining which stain type you are dealing with is important in determining the choice of chemicals to use to remove it. Generally, stains can be classified into three types:


Organic stains are caused by those materials which are derived from living organisms. For example, most foods, drinks, plants and some dyes are all considered organic stains. Organic stains include coffee, tea, coloring agents of dark sodas and other drinks, gravy, mustard, etc. Also, stains such as mold, mildew and other biologic material would fall under the organic stains category.


Inorganic stains are those materials which are not derived from living organisms. They are usually mineral in nature. They include things like ink, polymers and waxes, color dyes, dirt—water spilling over from flower or plant pots, etc. This category also includes non-organic oils, such as motor oil.


Metal stains include, iron, cooper, bronze, zinc, rust, etc. Although metal stains are considered inorganic, they may req

Why is the distinction between these stain types so important?

Inorganic stains are mineral in nature and so is natural stone, tile, and concrete. Iron is a compound found naturally in stone, some tile and concrete, and will oxidize, rust, and cause the surface to turn yellow, brown or red. This occurs quite frequently in white marble and some limestones.

If the stains are caused by oxidization of iron, it may not come out. This is not to say that organic stains are always easier to remove, but in this case you will know from the very start if the stain is worth trying to remove.

To determine if the stain is inorganic and caused by natural minerals can be difficult, but there are a few guidelines that can help.

First, if the stain has the same color and is spread entirely over the surface, then chances are it may be caused by external staining materials such as old wax, crystallization fluids, iron in the cleaning water, etc.

Does the stain follow a certain pattern? Many times rust will appear and follow a given pattern. For example, in Statuary white marble, iron will be noticed adjacent to veining, usually running alongside the length of the vein. If this is the case, it is a good indication that the iron is part of the stone and cannot be removed. If the problem is severe and further analysis is needed, then remove a section of stone. Carefully examine the section of stone and determine if the staining is on the surface only or through the entire stone. If the stain is all the way through the stone then it will be difficult or impossible to remove. Examine the setting bed where you removed the section of material. If it is stained, remove a portion of the setting bed to see how deep the stain is or to determine if the stain is coming from somewhere within the setting bed. Quite often, rebar, stray nails or screws will cause iron staining.

Refer to the Stain Chart for help on how to remove rust stains.

Organic stains can also be difficult to remove depending on their type. For example, when oil is absorbed into a porous surface, it can quickly spread throughout. On the surface it may look relatively small but can be spread all through the material. To illustrate this point, place several drops of oil on a light-colored marble or concrete. Wait several days and you will see how the oil spreads itself over the entire surface. This is important to realize when it comes time to remove the oil stain. Of course, the quicker you can get to a stain the less chance it will have to soak in.



A poultice is an absorbent material applied to a surface to draw out a stain. The poultice can be a powder, paper or a gel. The most common poultices in use today are powders. A number of powders are very absorbent and are ideal for stain removal.

Some typical powders used in poultices:

  • Clays and fullers earth
  • Talc
  • Chalk (whiting)
  • Sepiolite (hydrous magnesium silicate)
  • Diatomaceous earth (DE powder)
  • Methyl cellulose
  • Flour

Clays and diatomaceous earth are usually the best. Do not use whiting or clays containing iron. When using acidic chemicals, the acids will react with the iron and may cause yellowing of certain stone surfaces. It is best to purchase poultice powder materials from a reputable supplier of products for this purpose.

Some typical paper poultices are:

  • Cotton balls
  • Paper towels
  • Gauze pads

Paper poultices can be quite effective on mild stains. They are easier to apply than powder poultices and are also easier to remove.

Gel poultices are usually thick chemical gels that are designed to be applied to a stain with the use of powders or papers. They work effectively with certain stains.

When purchasing poultice products check to see if they contain stain removing chemicals or if they need chemicals added. Some powder and gel poultices contain chemicals, and all you need to do is add water. Never mix additional chemicals with a poultice that contains its own chemical formulation.


As stated in the beginning, the reason porous surfaces stain is because they are porous and staining agents can be absorbed into the pores. In order to remove the stain, this process must be reversed, and the stain must be sucked back out. The poultice is the material necessary to draw the stain back out. However, once the stain sets, it is very difficult to draw back out, so something must be used to loosen the stain. This loosening is accomplished by breaking down the stain with chemicals or reagents specific to the type of stain. Again, this is why it is important to identify the stain.