The Use of Limestone in your Shower

 

Limestone Use in Wet Areas

By Frederick M. Hueston

 

Over the past 30 years I have inspected hundreds if not thousands of shower installation that have use limestone.  The amount of deterioration I have observed in nearly all these installations ranged from staining to complete disintegration of the stone. Most will attempt to blame the installation method, but I can assure you these issues occur in installations that are installed within industry guidelines.

In a nutshell I would not recommend using limestone in wet areas. The following is why I would not recommend it

 

1.      Limestone is a sedimentary stone. It naturally contains minerals such as iron. When iron is exposed to continued wetting the iron will begin to oxidize causing a large stain. At first the stain may appear light brown but over time it will darken and continue to oxidize to a deep brown to reddish stain.  Removing the iron from the stone is nearly impossible since it is part of the mineral makeup of the stone.

2.      Limestone, even when sealed is typically very porous.  Water will enter the pores of the stone and react with the setting bed. The setting bed contains salts which become dissolved in the water. The water carries the salts into the pores of the stone. When the stone dries, the salts recrystallize causing pressure in the pores resulting in the stone blowing out(spalling).

3.      Limestone is an organic sedimentary rock that forms from the accumulation of shell, coral, algal, and fecal debris. It is formed by sediment settling to the bottom of a water basin. The main mineral is calcium carbonate.  Calcium carbonate can be soluble in water. This is yet another reason to avoid using limestone in a wet environment. Since it often contains organic matter, this too is soluble in water.

4.      Steam showers are even a bigger concern with limestone installation due to the fact the vapors produced by the steam can enter very tiny pores that liquid water cannot. The steam than condense in the pores causing the stone to deteriorate.

5.      The Natural Stone Institute, who is the leading trade association in the industry, recommends that only class A & B stones be used in interior wet areas. Limestone fall into a C class at best, Many fall into the D classification. For more info on this classification system go to The Natural Stone Institutes website at https://www.naturalstoneinstitute.org/

 

One may question the fact that limestone is used on building exteriors with no issues. This is true but there is a big difference. The average shower produces on average of over 8000 inches of water per year. To put this in perspective the rainiest area of earth is in China which has 321 inches of rain a year.. The average shower has over 26 times that amount. That’s a lot of water.

I have been in the stone business for over 35 years and have numerous colleges who agree that using limestone in a shower is not recommended.

MOISTURE-STONE ENEMY NUMBER ONE

           MOISTURE-STONE ENEMY NUMBER ONE

 

Most of the problems associated with stone tile installation can be traced to moisture or water intrusion of some kind. Many stains are caused by the presents of water. Water is an essential ingredient for the setting cleaning and restoration of stone but it can also be its number one enemy.

 What problems are associated with moisture and water.  The following is a brief description of the problems, there prevention and remedies:

 

 Efflorescence

 Efflorescence appears as a white powdery residue on the surface of the stone.  It is a common condition on new stone installations or when the stone is exposed to a large quantity of water, such as flooding.  This powder is a mineral salt from the setting bed.  To remove efflorescence do not use water, buff the stone with a clean polishing pad or #0000 steel wool pad.  The stone will continue to effloresce until it is completely dry.  This drying process can take several days to as long as one year.

 Subflorescene

Subflorescene is what happens when the mineral salts migrate and do not make it all the way to the surface. In the efflorescence condition above, the slats are deposited on the surface of the stone. In subflorescene the salts crystallize just below the surface, causing stress within the pores of the stone. The result is a condition known as spalling which appears as pits in the surface of the stone.  subflorescence is very common on green marbles and is very common on almost all stone surfaces where de-icing salts are used.

Iron Staining

 Many light colored stone contain naturally occurring deposits of iron.  Iron is a mineral  found in stone and can occur randomly throughout the stone.  If iron is present, it will begin to oxidize when exposed to water or other oxidizers such as acids and household bleach.  Stone can remain  for years without yellowing then over time may slowly turn yellow and in severe causes may turn completely brown.  This oxidation process is accelerated when the stone is saturated with water.  This process of oxidation is similar to the rusting of metal.  If you expose a brand new nail to water and air it will turn brown and rust.  The same process is occurring with the iron in the stone. If water and/ or air is eliminated the iron will not oxidize.  This is the reason certain white marble suddenly turn yellow.   The process is difficult to reverse and replacement of the stone may be necessary.  The following stain removal technique has proved successful in several cases.  Before testing this procedure it is important to first determine if iron is the cause.

  Testing for Iron:

1.  Before assuming the marble is yellowed due to iron be sure to attempt cleaning and stripping with a good alkaline based stripper.  If these procedures fail then testing for iron will be necessary.

 2.  If a flood has occurred or excessive water was used first check the water for iron.  There are several inexpensive test kits available that can be used to check the iron content in water.  Check with your local plumbing supply store or store carrying water softening supplies.  If any amount of iron is detected then it is possible iron has entered the stone through the water supply.  To eliminate the iron there are chelating chemicals that can be added to the water to prevent the iron from staining.  This is very important if the stone is cleaned with this water.

 3.  If the water contains no iron and even if it does the stone should be checked for iron content.  Remove a small sample of the stone  and contact a testing lab and have them analyzed it for total iron.  If there are spare tiles that have never been installed also have them tested for total iron.  If iron is present naturally in this stone, it will probably be detected in the spare tile.    If the results return with iron present then the following procedure should be tested.

 4.  Check the stone for moisture.  A moisture meter is a useful instrument that can be employed to check the stone for moisture.  If the stone contains water, it is very possible that iron is beginning to oxidize.

 Removing Iron Staining:

 1.  Prepare a solution of water and the following chemical: Sodium Hydro sulfite and Sodium Metabisulfite.  These chemicals are available in a product called Iron-Out(TM) from your plumbing supply or home center.  Mix a solution in water and apply to the effected area.  Allow solution to soak in and keep wet for several hours. Do not allow solution to dry.  After several hours pick up excess solution with a wet vacuum and rinse throughly with water and a chelating agent such as EDTA.  Be prepared to repolish any marble since these chemicals can cause etching.

 2.  If the above procedure fails than prepare a poultice with diatomaceous earth and the Iron Out(TM).  Mix the poultice into a thick paste and apply to a small area.  Cover the poultice with plastic and allow it to sit covered for 24 hours.  After 24 hours remove the poultice paste and rinse the area with water and a chelating agent.  If the stain is removed, the entire surface can be treated. If the stain still remains then replacement is the only solution.

 Before the above procedure can be performed, it is important that the effected area be dry.  If water or moisture are still present, oxidation of iron may continue

 The yellowing of stone is a common problem.  New installations should be sealed with a good quality penetrating sealer(impregnator) Which will help prevent oxidation of the iron by eliminating moisture.

 The above procedure has proven successful in some cases of iron staining however if the following test does not produce the desired results I would recommend replacement of the effected areas.

  Warping

 several type of thin stone tiles are very susceptible to warping. Many of the green marbles and a few agglomerate marbles are notorious for this warping condition.  Many of an installer have had the surprise to find that there tile installation has become warped overnight. Why does this a happen and can it be prevented.  Warping is caused by water. Green marble set with any water based material will have a tendency to warp.  The mechanism of why the tile warps is somewhat a mystery.  Some believe that the water fills the pores of the stone and when the water evaporates the orientation of the stones crystal change and cause it to warp.  Whatever the reason, one thing is for sure, green marble can warp when set with water based materials.

 Cure: Once a green marble tile warps it is difficult to repair. Attempts have been made to grind the tile flat , but this usually fails since additional water is introduced during the grinding process. The green simply warps again.

 Prevention; The only way to prevent warping is to install it properly with a non-water based material such as epoxy. Some installers have also ben successful in sealing the back of the tile with epoxy and installing it in a water based system(see July Stone & tile Report).  Do not attempt to seal the back of the tile with a silicone sealer.  The silicone acts as a water repellant and will cause the setting material to fail resulting in a bond loss.

 Erosion

 Erosion is a condition found when stone is exposed to constant amounts of water. This is especially true with marble that is used in water fountains.  While marble is a very decorative material, it is one of the worst materials to use in or around water.  Marble is composed of calcium carbonate. Calcium carbonate is a water soluble mineral. Quite simply this means it will dissolve in water. Want proof, visit the Grand Canyon.  Erosion can be recognized by a slow deterioration of the stone surface. With polished stone the polish will be worn off. In older installations, the stone may become very soft, brittle and in extreme conditions, it will powder.

If any architects or designers are reading this article I beg you no to use marble for water fountains.  If you do, plan on very high maintenance costs and plan on replacement in about five to ten years if not sooner.

 Stabilizing erosion:

 If your faced with trying to stabilize a marble fountain that is already deteriorated there are some treatment that can be applied that will extend the life of the marble. These treatments are general called consolidants and serve to replace the natural binders that are lost through erosion. Consolidants can be tricky and quite often will cause discoloration of the surface. Be sure to test the consolidant carefully before use.

 Mineral crusts or Lime Putty

 Mineral crusts or lime putty can be recognized by its white crust like formation on stone surfaces. These crusts are often found on outdoor stone stair, water fountains and other areas where stone is exposed to water. The crusts are a deposit of hard mineral salts consisting of calcium, magnesium. These minerals ordinate form the soil, setting bed or from the water itself. These salts are similar to efflorescence in that they are a mineral. They differ in that they form a hard crust that can be difficult to remove.

 Crust Removal

 there are only two ways to remove these mineral crusts. Abrasion or chemical.  The mineral salts should be remove with an abrasive. I have found that a stiff non-ferrous wire brush can work well.  Brushes can also be purchased that attach to an electric drill. Be careful and do not get to aggressive. Avoid damaging the stone surface.

Quite often abrasion alone will not remove all salt deposited. Strong Acidic chemicals will be required. These chemicals can be purchased from most chemical companies that supply stone cleaning products.  Be careful when using these products around calcium based stone since the acid can also damage the stone itself.

 Prevention.

 The best prevention from mineral salts is to prevent moisture form entering the stone.  On steps and fountains make sure all grout joints are caulked with a water proof material. When installing steps outdoors make sure a water proofing barrier is used. It is also a good idea to use a good stone impregnator on all surfaces to prevent water from entering the stone.  Caution; Stone inpregnators will not waterproof stone. Do Not use them where hydrostatic pressure is a concern.

 TESTING FOR MOISTURE

 To properly test for moisture a protimeter is necessary. A protimeter is an instrument that reads moisture. The common protimeter has been designed for use with wood, drywall and other similar substances.  The protimeter contains two sharp probes that are inserted into the wood or drywall to give a direct moisture reading in percent.  Unfortunilty you can not push these probes into the stone, but the protimeter can give you important data oon stone moisture.  By placing the pins so that the just touch the stone a relative reading can be obtained.  For example, A reading of 0-6% is considerely relativly dry. A reading between 7-20% is wet. A reading of of 20% is very wet.  These readings only tell you that the stone is wet, a little wet or dry. A direct percent reading can not be obtain with these instruments, but can provide useful information.

 Another simple technique for determining moisture in stone is to take a piece of plastic about 12 inches square and place it on the suspected stone. Tape all four edges and allow it to stay overnight or 12 hours.  After 12 hours, if there is any moisture present , you will see condensation collecting under the plastic.

 TESTING FOR SALT

 A protimeter can also be used to check for the presents of soluble salts.  The following procedure will only tell you that salts are present. It will not tell you how much or what type. But in many cases the simple presents of salts can indicate potential spalling and/or pitting.

 For this test you will need the following materials:

 

A rubber block

filter paper

distilled water

a protimeter

forceps

 

Any type of rubber will do as long as it is clean and does not contain any salts. A piece of hard plastic can also be used.  Filter paper can be purchased from a scientific supply store and sometimes from the supplier who sells protimeters.  Distilled water can be purchased from the grocery store.

The forceps are used to pick up the filter paper.

To check for soluble salts pick up a filter paper with the forceps. DO NOT touch the filter paper with your fingers. The human skin contains soluble salts which could be transferred to the paper giving a false reading.  Place the filter paper on the rubber block. Add a drop of two of distilled water to the filter paper. Place the probes of the protimeter to the filter paper and record the reading.  Next, take a new filter paper and place it on the stone to be tested. Add several drops of distilled water and take a reading. Record the reading on a piece of paper.

 If the reading obtained on the filter paper from the stone is higher, then there are slats present. If it is the same or lower, salts are absent.  The protimeter works by reading ionic changes. When salts are dissolved in water, the ionic changes are higher, which gives a higher reading.

  www.stoneforensics.com

Caring for your Concrete pool deck

 

Caring for your concrete pool deck

Frederick M. Hueston stoneforensics.com

Concrete is an ideal material for pool decks due to its durability, affordability, custom design capabilities, and environmental friendliness. It is perfect for high traffic areas like pools.

Just because concrete is low maintenance doesn't mean it requires no upkeep. Proper care is crucial to maintain its appearance, as the area has likely cost a significant amount of money. Neglecting debris, leaves, dirt, and potential animal intrusions can lead to damage if left unchecked. It's best to address any issues promptly.

Cleaning a concrete pool deck is not as challenging as commonly believed. With the correct tools and method, it can be easily maintained. It's important to keep some key considerations in mind during the process.

Cleaning Frequency

Concrete pool decks should typically be cleaned at least annually, but if the area is heavily used, more frequent cleaning may be required if stains appear.

Being a pool owner includes regular cleaning and maintenance. Initially, it may seem time-consuming, but with experience, you will learn effective methods to make the process more efficient.

Start the cleaning process by clearing the area of all furniture, pool toys, and other items. Remember that dirt and grime can accumulate under furniture and go unnoticed. This can cause mold or mildew spots if left untreated, so be thorough when cleaning to prevent future problems. Cleaning under furniture multiple times a year, even if not thoroughly, can prevent stains from developing and make future cleanings easier.

 How to Clean your pool deck

You'll need a few essential items in order to effectively finish cleaning the concrete pool deck. One of the most crucial tools is a pressure washer because it makes cleaning the area more quicker than trying to do it by hand. To get rid of any stains that have built up over time and are difficult to handle, you'll also need a cleaning solution and a scrub brush. You may either buy a concrete-safe commercial pool deck cleaning solution or prepare your own by combining warm water and dish soap.

If you decide to go this method, start with a ratio of 10 parts water to 1 part dish soap. For optimal results, use a light dish soap that degreases. When you start the procedure and realize the solution isn't strong enough, gradually add more soap to the mixture until the desired effects start to appear. To get the solution to work precisely how you need it to, it can require a little bit of trial and error.

For stubborn stains, mix the aforementioned dish soap with 1 cup of bleach per gallon of water. Below is further information on how to particularly remove stains.

Depending on the circumstance, you could also require a mop and a sizable, spotless bucket for combining your cleaning solution.

Following the removal of all furniture and other items from the pool deck, take the following actions:

• Use a pressure washer to thoroughly clean the pool deck. Make several passes as necessary, depending on how much debris has accumulated. Be careful not to use a zero tip on the pressure washer. Use a fan tip and hold it at least 24 inches from the surface of the deck.

Use your garden hose instead of a pressure washer if you don't have one available, but keep in mind that the job will take longer.

• In the big, clean bucket, combine your preferred concrete cleanser.

• Apply the cleanser with your mop to the entire concrete pool deck.

• Pressure wash once more as necessary to get rid of the extra cleaning agent.

 

Keep an eye on the appearance of your concrete pool deck before, during, and after this procedure. Particularly if you're not dealing with any challenging stains, you ought to notice a sizable difference immediately. To return your concrete pool deck to its previous appearance and sparkle, you'll need to repeat the procedure as often as necessary.

 

Stain Removal?

As previously mentioned, you will have to work on those challenging locations by hand to remove stains that have grown on your concrete pool deck. Apply the cleaning agent to the surface and scrub. If you're using a commercial cleaner, read the recommendations carefully because you might need to let it sit in the area for a while for it to work most effectively.

Then, using a scrub brush, manually remove the stains. Don't be afraid to exert some power; this is unquestionably one of those circumstances where a little bit of effort goes a long way. Do not be afraid to let the area dry and try again if the stains cannot be eliminated on the first attempt.

Safety is a crucial factor to take into account while using any kind of cleaning solution, whether it is manufactured at home or bought from a store. Rubber gloves should still be worn even when you're outside and in an area that should be adequately ventilated to prevent coming into contact with the solution. Additionally advised as an additional layer of defense is eye protection. To prevent breathing in the fumes from the solution that can develop, several specialists even wear breathing masks.

Use your pressure washer to rinse the area one more to eliminate any remaining solution when you are certain that the stain has been removed and the concrete pool deck is as clean as you want it to be. Avoid coming into contact with any flowerbeds, trees, or other plants that may be a part of your landscape while carrying out this task. It's possible that the extra cleaning solution will hurt them. Additionally, you should refrain from touching the pool area's furniture during this time because the solution, particularly one that contains bleach, may result in long-term problems.

Maintaining the pool deck

You must carry out this kind of deep cleaning at least once a year, if not more frequently, to maintain your concrete pool deck. Many pool owners clean their pools twice a year, in the spring and the fall. If there has been a lot of foot traffic in the area, if soil is routinely moved onto the deck, or if there is a lot of trash buildup from nearby trees or plants, you might need to do this more frequently.

Also keep in mind that having animals around could make cleaning more necessary frequently. It's best to address the issue now rather than waiting for an eventual long-term problem to arise because animal droppings can quickly result in stains.

If you haven't already, consider spending money on a waterproof deck coating for your concrete pool deck to make the process simpler in the future. This helps to make the area easier to clean in general and can help to keep surfaces stain-free even when they are heavily used. Your pool deck will last longer and look better over the entire season, just as it should.

This is important to remember because unfinished concrete is porous by nature. Because of this, things like a pool deck made of unsealed concrete are naturally prone to mold and mildew. The problem is only made worse by the fact that this surface is situated next to a sizable body of water. Similar to how you can prevent immediate problems, avoid keeping wet towels, cloths, or other damp items on the surface itself.

Additionally, you should fight the impulse to grow big plants right next to your concrete pool deck. This will lessen the possibility of root injury.

When possible, always take out everything composed of metal from your concrete pool deck. With so much moisture present, even little objects can rust, staining the concrete deck surface.

Finally, you should take care of any little cracks or chips in the concrete pool deck that you uncover throughout the year to help make cleaning simpler and prevent long-term damage. Even if a tiny crack doesn't affect you particularly, you should nonetheless fix it right away. Almost always, small problems will grow into much larger ones that are far more difficult and expensive to resolve. They may also pose possible risks to the safety of those using the pool's perimeter.

 

 

Why is my Grout Turning Yellow

Why is My Client’s Grout Turning Yellow?

By Frederick M. Hueston, Stone Forensics

Over the years I have received many calls from stone and tile restoration professionals asking how to identify the cause of grout yellowing and resolve grout yellowing problems. The reasons for this discoloration are many. Testing can help determine what is causing the problem. Solutions vary, depending on the cause. Here are the details.

Top Ten Reasons for Grout Yellowing

1.      Shampoos, soaps, etc. – Many of the personal items your clients use contain chemicals that can cause discoloration, and hence yellowing of grout. This is especially true of hair dyes and shampoos that contain coloring agents.

2.      Body oils – Skin and hair oils contain many contaminants that can cause discoloration of not only grout but also tile. These body oils are what cause the familiar yellow stain, ring-around-the-collar.

3.      Sealers and waxes – Sealers and various waxes can contain polymers that can discolor over time and cause yellowing.

4.      Grout types – There are numerous grout types that are prone to yellowing. White epoxy grouts are notorious for turning yellow.

5.      Cleaning products – Certain cleaners, especially those that contain dyes, can cause discoloration of grout. Household bleach commonly discolors grout.

6.      Iron – Certain water supplies contain iron. Water containing iron can deposit minerals on the grout that can oxidize and cause a yellow discoloration. If the water used to mix the grout during installation contained iron this can also cause discoloration. Check your water supply for iron.

7.      Dirty water – Water used to mop floors can rapidly get dirty. The dirt, oils, etc. will settle on the grout lines and cause a yellow cast. Encourage your client, or the cleaning or janitorial services they use, to keep mop heads clean and change mop water often.

8.      Smoke – Cigarette smoke can settle on grout lines, causing the grout to turn yellow.

9.      Aerosol sprays – Sometimes aerosol sprays, such as hair sprays and even air fresheners, cause grout discoloration.

10.   Bleed over – Certain tile types, such as white marble, contain iron. Iron from the tile can bleed into the grout and oxidize, causing the grout to turn yellow.

How to Test for Yellowing

As mentioned above, there are many reasons why grout can turn yellow. Here are some suggestions for inspecting the grout to determine the cause:

1.      Determine what cleaning products and toiletries have been used in the area. Look up the SDS on the product to determine whether products contain dyes, polymers, or other ingredients that may cause grout to turn yellow.

2.      Test the grout lines for iron using a product from Alpha Tools called RSR 2000. Place a small dab on the grout and wait several minutes. If it turns purple, it is positive for iron.

3.      Test the water for iron if iron oxidation is suspected. Test kits can be purchased at most home centers or water supply stores. If iron is present in the water, suggest that your client install a water filtration system.

4.      Try to determine the grout type. Epoxy grout can be problematic.

5.      Take a knife and scrape the grout. Examine the scraped area to see if the discoloration is on the surface or all the way through. Surface discoloration usually indicates chemical discoloration.

Once the cause of grout yellowing is determined, you can attempt to resolve grout yellowing problems. Be sure to instruct your client about using preventative measures such as discontinuing the use of stain-causing products, smoking outside, installing a water filtration system, etc.

How to Clean Yellowed Grout

To clean yellowed grout, you will need sulfamic acid, which can be purchased at most home centers and can also be found at most tile supply companies, and a good floor wax stripper, which can be purchased at most janitorial supply houses. Ask for an alkaline-based floor wax stripper. Caution: Sulfamic acid will damage marble surfaces.

Here are cleaning instructions:

1. Sweep the floor thoroughly, removing any loose dirt, dust, etc. For showers and walls, wipe with a dry rag.

2. In a cleaning pail, mix warm water and a good floor cleaner or ammonia. For showers and walls, use a clean rag and for floors, use a clean mop to clean the grout. Empty the pail.

3. Next, mix alkaline stripper with warm water, being sure to follow the directions on the bottle.

4. Apply a small amount of this solution to the grout. Allow it to stand for several minutes. Agitate the solution with a scrub brush, toothbrush, or similar type brush. Apply additional solution if the grout begins to dry.

5. Pick up any excess solution with a mop or a wet vacuum.

6. Rinse the grout with plain, warm water. Empty the pail.

7. Mix sulfamic acid with warm water, per the directions on the label.

8. Apply the acid solution to the grout and agitate.

9. Rinse the grout several times with clean water and allow to dry overnight.

10. Once dry, seal the grout with a good penetrating sealer.

If the above technique does not work and the grout is in good condition and not falling apart, then apply a high-quality grout color sealer. As a last resort, remove and replace the grout.

Natural Stone Tiles the Confusion Surrounding Sealing

 

Natural Stone Tiles the Confusion Surrounding Sealing

By Frederick M. Hueston, StoneForensics.com

 

There would seem based my own experience that there is a lot of confusion amongst the general public and some builders as to what sealing natural stone actually means.

When we talk about sealing a surface we normally mean that an impenetrable barrier is painted on or applied in some way. For example, tiled floors are often sealed to give them added protection and make them shine. To do this a series of coats of emulsion polish are applied to the surface and allowed to dry. This seals the floor and gives it protection. Other surfaces such as wood are often sealed with a coating of a polyurethane product. This adds strength to the surface and protects it. Many other normally porous surfaces can be sealed with a layer that sits on the surface acting as a barrier to penetrative agents and gives protection also.

The sealing of natural stone such as marble, granite, limestone and slate is very different. Natural stone is made up of crystals that interlock together. The actual minerals that are present as crystals in the stone give it its color and striations. However, there are spaces between the crystal and the smaller these spaces are and the more the crystals have been compacted together the less porous the stone is. So, these spaces will determine the porosity of the stone. A combination of pore size and mineral content of the stone will also determine its hardness and thus its durability. These spaces in the stone are air filled when the stone is dry and water filled when the stone is wet. Bacteria inhabit these spaces, and these are often vital for the maintenance of the stone. Very little research has been carried out into these bacteria but what has been done would suggest that they are essential in maintaining the integrity of the stone.

Consequently, we have the picture of stone as quite a complex mix of minerals, bacteria and spaces. You must imagine the stone to be something akin to a very hard sponge! If you drop a liquid onto the stone it will be absorbed and spread through the spaces. This is why what initially looked like a small spillage can end up as quite a large stain in the stone. To remove the stain it has to be flushed out of these spaces. All a stone sealer does it fill up these spaces. Many of the stone sealants in use are based on fatty acids rather than synthetic sealants. These natural sealants are better because they do not destroy the bacteria but often enhance them. Synthetic sealants will destroy these bacteria that has longer-term consequences on the stones makeup. Sealants based on fat however have a shorter lifespan and must be renewed periodically.

Whatever sealant is used it simply fills up the spaces between the crystals it does not cover the surface of the stone. Its purpose is simply to delay the penetration of liquids into the stone. So if corrosive materials get onto the stone then it will be damaged. Stone sealants do not form a protective seal on the surface of the stone. Consequently stone is only protected from absorbing liquids. It is not protected from surface damage.

 

OXIDATION OF ELEMENTAL IRON WITHIN STONE SURFACES(YELLOWING OF STONE SURFACES)

OXIDATION OF ELEMENTAL IRON WITHIN STONE

SURFACES(YELLOWING OF STONE SURFACES)

Frederick M. Hueston 

Sitting in my office one morning I received a call from a very upset homebuilder. He told me he was building a

two million-dollar home on the west coast of Florida. They installed nearly 3500 square feet of a white statuary

marble tile. Over the weekend one of the water pipes broke in a bathroom and completely flooded the home.

They managed to vacuum all the water and started to access the damages. Beside warped wood, soaked drywall

and an irate homeowner the marble tile seemed fine except for some minor water spotting. After several weeks

the replacement of warped wood and drywall began and then he noticed the white marble tile turning yellow. At

first he thought it might be some type of residue so they tried cleaning the marble with some bleach and waterthe

yellowing was still there. The homeowner was getting more and more irate and was threatening a lawsuit.

He asked if I could get down there right away and take a look at the marble and suggest what to do.

The above story is not uncommon and is a frequent occurrence on white marble tiles exposed to flooding. Can

the yellowing be removed or does it need to be replaced? What causes the yellowing and will it get worse. The

following is an explanation of yellowing in white marble and some techniques that may help.

Why Does White Marble Turn Yellow?

The problem of yellowed white marble is not uncommon. All over the United States I have encountered yellow

to brown marble. Although flooding is a common cause there are several other reasons this color change will

occur.

1. Improper Maintenance- As marble wears the highly polished surface begins to disappear. The wearing of

this polish causes the surface to become rough and is a magnet for dirt. If improper cleaners are used, this dirt

begins to accumulate in the pores of the stone and will turn yellow. It is surprising how often I have seen this

condition on marble. Upon investigation in these cases I have found dirty mops being used. Mops used to

clean the restrooms and/or kitchens were also used to clean the marble floors. Floors are mopped with strong

cleaners or wax cleaner combinations or with no cleaners at all.

Cure: If you suspect yellowing due to improper maintenance the marble tile will have to be cleaned with an

alkaline marble cleaner. I would suggest a heavy duty stone cleaner. Be sure the stone cleaner you buy is

alkaline and not an acid since acid cleaners will dull the polish. Apply the cleaner to the marble and scrub with

a soft brush. Be sure to rinse the floor throughly. It may be necessary to repeat this procedure several times to

remove all the imbedded dirt. If after cleaning the marble is dull I would suggest re-polishing and an

application of a good quality penetrating sealer(impregnator). If after several cleaning’s the yellowing is not

removed than proceed to the next cause.

2. Wax Build-up or Coatings- Many marble floors are coated with waxes, acrylics, urethane and other coatings.

Many of these coatings are not specifically designed for use on marble floors. Some of these coatings are of

poor quality and will begin to yellow. It is not uncommon for coating to be applied in multiple coats. As the

coating builds up it becomes soft and dirt is easily embedded in the soft layer. These coatings require frequent

stripping which is often neglected.

Another process used for polishing marble floors is a process known as recrystallazation. If this process is

applied to a white marble floor that contains moisture it will turn the marble yellow. If this process is to be

used, it is important that the marble be dry.

CURE: To remove yellowing due to a wax or coating buildup the marble will need to stripped with a

commercial wax stripper. I would strongly suggest using a stripper manufactured by the same company as the

floor wax or coating. This will help avoid incompatibility problems. Follow the directions on the stripper’s

label and be sure to rinse the floor throughly. These strippers often require the use of abrasive pads which can

scratch and damage the marble surface. Before undertaking the entire project perform a small test to determine

results.

If the marble tile has been recrystallized, it will be necessary to remove the recrystallized layer. This layer can

often be removed by polishing the tile with a powder marble polish containing oxalic acid. Apply the powder to

the tile, added water and work into a slurry with a hog hair pad and a standard buffing machine. Continue to

work until yellowing has disappeared. If this technique fails then the tile will have to be re-honed. It is strongly

suggested that the polishing and honing procedure be performed by trained individuals. If these techniques fail

to remove the yellowing then proceed to the next cause.

3. Iron Staining- Many white marble tiles contain naturally occurring deposits of iron. Iron is a mineral found

in stone and can occur randomly throughout the stone. If iron is present in the marble tile, it will begin to

oxidize when exposed to water or other oxidizers such as acids and household bleach. White marble tiles can

remain on a floor for years without yellowing then over time may slowly turn yellow and in severe causes may

turn completely brown. This oxidation process is accelerated when the tile is saturated as in the flood in the

above example. This process of oxidation is similar to the rusting of metal. If you expose a brand new nail to

water and air it will turn brown and rust. The same process is occurring with the iron in the marble. If water

and/ or air is eliminated the iron will not oxidize. This is the reason certain white marble suddenly turn yellow.

The process is difficult to reverse and replacement of the tile may be necessary. The following stain removal

technique has proved successful in several cases. Before testing this procedure it is important to first determine

if iron is the cause.

Testing for Iron:

1. Before assuming the marble is yellowed due to iron be sure to attempt cleaning and stripping as outlined in

#1 & 2 cause above. If these procedures fail then testing for iron will be necessary.

2. If a flood has occurred or excessive water was used first check the water for iron. There are several

inexpensive test kits available that can be used to check the iron content in water. Check with your local

plumbing supply store or store carrying water softening supplies. If any amount of iron is detected then it is

possible iron has entered the stone through the water supply. To eliminate the iron there are chelating chemicals

that can be added to the water to prevent the iron from staining. This is very important if the tile is cleaned withthis water.

3. If the water contains no iron and even if it does the tile should be checked for iron content. Remove one tile

and contact a testing lab and have them analyzed the tile for total iron. If there are spare tiles that have never

been installed also have them tested for total iron. If iron is present naturally in this stone, it will probably be

detected in the spare tile. If the results return with iron present then the following procedure should be tested.

4. Check the tile for moisture. A moisture meter is a useful instrument that can be employed to check the tile

for moisture. If the tile contains water, it is very possible that iron is beginning to oxidize.

Removing Iron Staining:

1. Prepare a solution of water and the following chemical: Sodium Hydro sulfite and Sodium Metabisulfite.

These chemicals are available in a product called Iron-Out(TM) from your plumbing supply or home center.

Mix a solution in water and apply to the effected tile. Allow solution to soak into tile and keep wet for several

hours. Do not allow solution to dry. After several hours pick up excess solution with a wet vacuum and rinse

throughly with water and a chelating agent such as EDTA. Be prepared to repolish the marble since these

chemicals can cause etching.

2. If the above procedure fails than prepare a poultice with diatomaceous earth and the Iron Out(TM). Mix the

poultice into a thick paste and apply to a small area. Cover the poultice with plastic and allow it to sit covered

for 24 hours. After 24 hours remove the poultice paste and rinse the area with water and a chelating agent. If

the stain is removed, the entire floor can be treated. If the stain still remains then replacement is the only

solution.

3. There are also some new chemicals that are available which contain Ammonium Thioglycolate which look

promising for removing iron oxidation. Check with several stone maintenance supply companies.

Before the above procedure can be performed, it is important that the effected tiles be dry. If water or moisture

are still present, oxidation of iron may continue

The yellowing of white marble is a common problem. New installations should be sealed with a good quality

penetrating sealer(impregnator) Which will help prevent oxidation of the iron by eliminating moisture.

The above procedure has proven successful in some cases of iron staining however if the outlined test does not

produce the desired results I would recommend replacement of the effected tiles.

Written by:

Frederick M. Hueston

Stone Forensics

www.stoneforensics.com