Removing Stains from Natural Stone

Stains on natural stone surfaces are a very common cause of concern among our Cleveland customers. Depending on the type of stone, it can be very difficult to properly remove a stain if it is not treated promptly and with the correct chemicals. The more porous the stone, the more susceptible they are to staining and the harder they can be to clean. Honed and textured stone like sandstone tend to be more porous than polished finishes like marble and granite. Properly identifying the cause of the stain, determining if the stain is actually a stain and finding the correct type of chemical to use to remove the stain will be your best chance to properly restoring your stone surface.

Identifying the Stain

Stains are typically categorized as two different types: organic and inorganic. Organic stains include materials such as food, beverages, plants (algae, mildew), tobacco, oil and grease. Inorganic stains typically include rust, iron, copper and minerals. Organic stains are typically much easier to clean than inorganic stains. Both inorganic stains and natural stones are mineral based. Iron is a mineral that is typically found in stone, so oxidation can often cause discoloration in your surfaces that is very difficult to remove. The size and age of the stain can also help determine if it is worth trying to remove it. If the staining appears to run all the way through the surface, it may need to be replaced. Organic stains such as oil can also be very difficult to remove if the area is not immediately treated. Always address any potential stains immediately after they happen.

Stains that are Not Stains

There are several conditions that can occur in natural stone surfaces that are commonly mistaken for stains. It is very important to be able to distinguish between these different conditions. If you are treating a natural stone for stain removal, there is a chance you can do further damage to the stone if you are trying to remove something that is not a stain.

Etching occurs when something acidic comes in contact with marble. This is caused by acid reacting to the calcium carbonate in marble, which eats away a part of the top layer. This creates dull spots in the marble. Stain removal does NOT remove etching. Etching can only be removed by honing and polishing the marble.

Water Spots or Water Rings are commonly caused by slightly acidic liquids from drinking glasses running down the sides and causing etching. This can also be caused by liquids that deposit minerals on the stone. These are called hard water spots. Similar to etching, these can also be removed by honing and polishing.

Efflorescence appears as a white powder-like substance on the top of stone. This is caused by minerals that are left over after a stone surface is wet. This often happens after installation of the stone surface. Depending on the type of surface and finish on that surface is what determines the type of chemical that should be used the efflorescence.

Stuns or crystalline fractures are white marks on natural stone that are usually beneath the surface – sometimes all the way through the stone. This is caused by an explosion of crystals in the natural stone, similar to when glass is shattered. This is commonly caused by dropping a heavy object on the natural stone.  These can also be created by high-heeled shoes, when the natural stone surface is on a floor. Stuns can be very difficult to get out depending on how deep they go through the surface.

How to Remove Stains

So how do you remove a stain from natural stone? The most common thing used to remove stains from natural stone is called a poultice.  A poultice consists an absorbent material (some type of powder) that is mixed with a specific type of chemical (depending on the type of stain).  The poultice is mixed up and applied to stone to try and draw the stain out of the natural stone. A poultice can be made from a powder, gel or paper. Powder-based poultices are the most commonly used today, with many pre-made poultices available to the average consumer. Most pre-made poultices are ready to use after mixing and some require the addition of water.  If you are going to create your own poultice, make sure you know:  what created the stain, the best chemicals to breakdown the stain (make sure that chemical is safe to use on your specific type of natural stone) and that you have a powder that is absorbent enough to draw the stain out of the natural stone.

How to Apply a Poultice

1. Identify the stain:  Knowing what type of stain you are trying to remove is half the battle. This will help you select the correct type of poultice to use.
2. Clean the stained area:  Clean the surface with a good stone cleaner with a neutral pH to remove any residue that may reside on the surface. If the stain is only on the surface then the poultice may not be necessary.
3. Remove coatings:  If the stone has been coated with any coatings such as an:  acrylics, urethane, epoxy or wax – it is important to strip them before applying the poultice. They can interfere with the chemical’s ability to remove the stain.
4. Pre-wet:  Wet the stained area with distilled water so the chemicals will not dry too fast.
5. Prepare the poultice:  When using a powder poultice, mix the powder with the needed chemical until it is the consistency of peanut butter. Gel does not require prior preparation before application.
6. Apply the poultice:  Carefully apply the poultice over the stained area. Overlap the poultice so it is about ¼ inch thick.
7. Cover the poultice:  Use plastic to cover the poultice and tape down the edges. This prevents the poultice from drying too quickly.
8. Remove cover & poultice: After about 24 hours, remove the plastic. After the poultice is thoroughly dry, carefully scrape it off with a razor blade.
9. Examine the area and reapply poultice:  Carefully examine the stained area. If the stain is not yet removed, reapply the poultice. It may take several tries to remove the stain. If after two applications, you do not see any improvement – you may be using the wrong kind of chemical.

At GK’s Custom Polishing, Inc., we are experts when it comes to the maintenance and restoration of natural stone, ceramic tile, concrete and most other hard surfaces. If you have any questions about cleaning, sealing, polishing, refinishing or maintenance of your surfaces, give us a call at (440) 937-4457 and speak with our talented team of experts.

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