Will the Wet Spots on my recent Marble Slab Installation go Away?

QUESTION

My contractor has installed moon face marble slabs approx 6 ft wide and 10 ft tall in my office entry. There are numerous unsightly wet spots still visible since installation 4 days ago. I’m told it’s the plaster leaching thru and will dry. Is this reasonable?

ANSWER

ANSWER - If you have a number of wet/dark spots on your newly installed marble slabs, it may be that the marble slab was installed in a spot bonded method.

If the marble slab was installed on a wall, it is possible that they mechanically attached the marble to the wall with wire.  When they do that they might use a plaster or a thin-set mortar to around the mechanical attachment to stabilize it and to allow then to adjust the levelness/plumbness of the slab on the wall.

If the marble slab was installed on the floor, then the spot bonded method is not considered an appropriate installation method.  This is because it leaves a lot of voids under the marble that would have a propensity to be damaged if those unsupported spots where subjected to some impact or heavy load.

A wet a thin-set mortar or plaster could transfer moisture to a stone and cause it to turn dark at the point of contact, but you would expect it to dry and go away.  Normally moisture will not migrate through a true marble because it has such a low absorption of 0.2% or less.

I have seen some cases where a certain type of mortar/plaster or mastic was used for the spots and it actually stained the stone where it was not removable.  This is a case of incompatibility between the adhesive and stone.  The installer or specifier of the adhesive should have verified the compatibility of the products.

The only think you can do now is wait and see if the spots diminish or go away.  I would put a measuring device next to them and take photos with dates on them, so you can compare them in a few weeks to see if they have changed.

 

42 thoughts on “Will the Wet Spots on my recent Marble Slab Installation go Away?

  1. Angelo says:

    Thinking of using marble tile for walls in a shower stall. It’s a cottage in Muskoka Ontario. Plan would be to seal the marble. My question is, what is the effect of natural lake water on marble vs treated city water.

    • Edward says:

      We had a light colored Quartzite installed last week (Bianco Superiore, also seen it called Mont Blanc). A day after the installation, we noticed on the rectangular island piece two parallel, and relatively uniform, 1 inch wide “lines” spaced a few feet apart that run halfway down the piece. Also a 3×5 sticker shaped lighter area in the corner of that same slab. These areas are visible because they are a few shades lighter than the surrounding stone. We were told by the fabricator that this particular slab was received from the stone supplier very wet from – we were told it was stored outside at some point after we selected it and got rained on. We did not see these “lines” at all when we picked out the stone at the stone supplier, and we didn’t see anything when visited the supplier prior to templating, although again the stone was soaking wet. This piece is a few shades darker than it was when we picked it out, so my sense is that it may still be holding some of that raine/moisture. The fabricator says the stone was quite wet, and needs at least 3 weeks to dry out. Any thoughts on what these “lines” could be, and whether they will fade as the stone drys and/or whether they can be polished out? My theory is that these “lines” are the shape of whatever storage bars/spacers were used to hold the stone during storage (and the 3×5 area was probably a sticker), and these areas were shielded from the rain so didn’t get as wet as the non-covered areas. Just a theory. Thank you!

      • Donato Pompo says:

        True quartzite is very dense and low absorption. Per ASTM C616 for Quartz stones, a quartzite can’t have an absorption greater than 1% which is almost impervious. So it can’t absorb much water and whatever little water it can absorb would dry quickly.

        Stone is a natural product and will naturally have various inclusions that might not be obvious at first. It is stone that has developed over millions of years. If there were some surface stain from storage bars it would have been removed during the polishing process. If there is a surface stain, which is unlikely, it should be easy to polish it to remove it. If it is an inclusion then it likely goes through the entire stone.

  2. Donato Pompo says:

    Natural Lake Water chemistry will vary from lake to lake depending on its water source and what it has been subjected to. Same with treated city water as we know from recent situations where city water can be contaminated due to various situations.

    Some water will have higher concentrations of minerals and is considered hard water that has higher concentrations of calcium and magnesium. Hard water can cause buildup in pipes and can leave residuals on surfaces that need to be cleaned more frequently.

    Best thing to do is have the water tested. You can also experiment with it on samples of the material you want to use.

  3. Margaret Dowd says:

    We recently had our shower redone with white and gray Bianca marble tile. The tile is now turning a darker gray near the drain area and also two brown spots have appeared. The contractor says we must have used some cleaner but all I used was a wet rag. He says he has never seen this happen. Help

    • Donato Pompo says:

      Chances are that the darker gray area near the drain is due to the installer either did not protect the drain weep holes to allow water under the stone to evacuate into the drain or he used a drain that did not have weep holes. Only way to fix it is remove the stones around the drain and unplug the weep holes.

      The brown spots are likely rust spots. White marbles typically contain iron sulfide minerals that can cause rusting if they are exposed to excessive moisture. Or there could be a metal attachment beneath the stone that can cause rusting. If it is surface staining it can normally be cleaned with a poultice. Best to have a professional stone restoration person do the cleaning.

      • Jim says:

        Hi, we had Carrara Marble installed throughout our bathroom remodel. Unfortunately before completion, one of the new shower diverter valves leaked behind the shower wall when the temporary cap failed (probably for more than 24 hours). Now we have darker floor tile (Carrara Marble) all around the exterior of the shower curbing. I’m guessing water got below the shower pan, above whatever cement they applied, and above the subfloor. We have the ceiling ripped out below the shower and have been drying for a couple of weeks with fans and dehumidifiers (for the first week). I think the subfloor wood is dry. We also have fans blowing on the top of the floor tile, along with turning on the new in-floor heating (electrical). So far the darker tile has only expanded its reach, though perhaps it has stopped advancing in the last few day. The flooring contractor advises it may take a month, but it will dry out. The restoration company is mildly but not overly concerned about mold, because it is all new construction (we were down to the studs with the remodel) and it was clean water. Initially after the leak, we also had similar dark tile in the vertical wall of the shower underneath and adjacent to the leaking valve but that has virtually disappeared (most likely gravity and we have the back of that wall ripped out with fans drying it (it’s dry there now)). Thoughts? Suggestions? — Many thanks for any advice or insights.

        • Donato Pompo says:

          Carrara Marble should be very dense and absorb more than 0.2% per ASTM C503 standard. But it can absorb a little bit.

          Normally if marble gets damp it can darken a little, but it should dry out. Unless it absorbs a stain from something. If the water comes into contact with one of the other underlying materials it could possible pick up a stain that can be absorbed into the marble. When the marble dries the moisture evaporates and the stain could stay within the marble.

          This isn’t typical. Marble is used all the time inside showers and it doesn’t cause staining. Although sometimes marble can show some yellowish stain from the natural occurring iron sulfide (pyrite) that marbles often contain. This stain normally occurs if the marble is subjected to excessive moisture for a prolong time; if the marble has a higher concentration of the pyrite.

          I would not expect it to take weeks for a damp marble to dry out. It depends on temperature, humidity, wind and etc. to determine how long it takes to dry. If it is a stain you can try using a poultice to draw out the stain. There is no set method for removing a stain. It requires and trial and error approach.

          • Jim says:

            Many thanks. I think we will wait and see what happens before removing the flooring. Do you think removing some of the grout might help drying, perhaps especially along the joint between the shower curbing and the floor?

          • Donato Pompo says:

            The joint between the shower curb and floor should be filled with an ASTM C920 sealant (caulking) as that is a transition joint.

            If the marble is installed over shower floor and it is remaining dark, it might be due to the weep holes at the waterproof membrane are plugged. They are suppose to be protected so excess water can drain away. The membrane is suppose to have a slope to drain of 1/4″ per foot. If those conditions are missing then the mortar bed might be retaining excessive moisture and isn’t able to full dry.

            Only way to determine that is to remove some stones and inspect those underlying conditions.

  4. Cilla Zosa says:

    Hi! I have a Carrera marble bathroom countertop. I now know it’s not sealed. A dark grey ring formed I believe from water sitting on top under a soap holder. How long does it tak to dry out, and is there something I can do?

    • Donato Pompo says:

      People tend to refer to marble as a soft stone, but it is far from it. Per the ASTM C503 standard the minimum density should be 162 lb/ft3 and the minimum absorption is 0.2% which is below the minimum absorption for being impervious.

      Although marble being a a calcium carbonate material is susceptible to scratching and sensitive to acid that can etch its surface. Chances are the dark grey ring isn’t a damp spot because the marble is impervious, but it could be an etched condition. Etched meaning it chemically altered the material. So it should feel like it has some texture when you rub your fingers across the spot.

      The good news is natural stone typically can be restored to being like new. A professional stone restoration company can deep clean, grind and re-polish the marble. Sealers can help, but they won’t prevent etching or staining. What is important is that you wipe up any spills right away. The soap holder should be set on top of a cloth to protect the marble.

    • Donato Pompo says:

      Do not use bleach for cleaning the marble. It can bleach and etch the the marble surface that would require repolishing the marble to repair it.

      Use a neutral detergent in water to clean the marble floor. Use a soft bristle brush on an extended handle to scrub it clean. Use a wet vacuum to pick up the dirty water. Then rinse the the floor with clean water and pick it up with a wet vacuum. Then buff dry the tile with a lint free cloth.

      After the marble tile is clean and dry apply a penetrating sealer. Be sure to apply the sealer with a lint free cloth and immediately after applying the sealer, buff it dry with a lint free cloth not leaving any damp sealer on the surface of the tile.

  5. SARFRAZ says:

    WE INSTALLED ROYAL GREY GRANITE ON THE FLOORING AND THICKNESSES IS 2 CM AND 3 CM AT VARIOUS AREA .
    FIRST DAY OF INSTALLATION GRANITE DID NOT CHANGE THE COLOR ,BUT AFTER COUPLE OF DAYS SOME PCS OR DARK SHADE LOOK THERE IS MOISTURE’S PENETRATES EITHER FROM THE TOP OR BOTTOM THAT IS BIG WORRY FOR ME. I NEED SOLUTION .THE GRANITE INSTALLATION HAS BEEN COMPLETED THREE MONTH BACK BUT 50 PERCENT OF FLOORING HAVE TWO VARIOUS SHADE.
    I NEEDS STRONG RECOMMENDATION TO SOLVE THIS PROBLEM IMMEDIATELY.

    • Donato Pompo says:

      To determine why some of the granite tiles turned dark would require performing a forensic intrusive inspection to evaluate the underlying conditions.

      Granite is normally impervious and do not readily absorb moisture, but here are some commercial granites that are not true granites that are more porous. Depending on whether the stone was installed and the application could suggest the stone is being subjected to excessive moisture depending the underlying conditions. Whether it is installed in an exterior application or an interior application in a wet environment or depending whether there is a vapor barrier under the house foundation can be factors. You can’t determine how to fix it until you have determined what caused.

  6. Chris says:

    We installed Carrara marble tiles in our bathrooms. The tiles have gone completely dark grey. We have fans and blowers in day and night for the last 3 days and we are seeing some drying occur. Will the tile dry out? Also is it best to wait for it to dry out before we seal the tiles?

    • Donato Pompo says:

      True marble is very dense and low absorption. Per ASTM C503 it should not have an absorption higher than 0.2 percent, which is technically impervious. Although it still absorbs slightly.

      So the marble can’t absorb much; thus it should dry out fast if the water is at the surface of the stone. If it doesn’t dry out fast then you might think the water is coming from behind, but it would take a lot of moisture to reach the front side of the stone.

      So the question is how was the shower constructed? Does it have a thick mortar bed or another type of absorbing substrate that would retain moisture? You should use a electronic moisture meter or an infrared camera to survey the stone to see if there are higher or lower areas of moisture indicating where the source might be coming from.

      Or is this some type of staining that is occurring? Marble has many natural minerals that can react with moisture to cause various types of staining. It is more typical to get a yellow/orange stain from the iron sulfide that marble tends to contain that will cause a rust-like stain.

      All you can do it continue to dry the shower and see if it makes a difference. If it doesn’t then you have to have an experienced forensic investigator such as CTaSC to remove tiles and look for evidence of what might be causing the condition. You can also have a laboratory perform a petrography to look for evidence of what is causing the darkening. Of course that might not be practical in terms of the costs involved.

      Normally you don’t want to seal any stone unless it is dry and clean. If you seal over a dirty stone then you can easily clean the dirt off. Sealers don’t last for ever and don’t make the stone waterproof, but they do help repel water. So I would seal the stone once it dries to your satisfaction.

  7. Dona Marie Johnson-Beach says:

    Could I send you a pic of a problem I am seeing in my shower? There’s a darkening of a marble shower slab. From what I am reading – I am wondering if water is leaking from the diverter.

    • Donato Pompo says:

      Looking at a photo wouldn’t help determine the source of the moisture. The only thing you can do is trouble shoot it as described above either yourself or higher a professional company like CTaSC.com to trouble shoot it. It can be an expensive process so it may or may not be practical to hire an expert.

  8. Mike says:

    I recently had a Carrara marble tiled floor installed in my bathroom. The tiles were installed over a ditra mat with underfloor heating. The tiles look great but when I turn the under floor heating on, darker spots appear on the tiles which look consistent from where the UFH wires would be. The spots are not everywhere, just random areas. When the UFH is turned off, the darker spots slowly disappear again. I have not sealed the marble yet as unsure what this problem may be. Any recommendations?

    • Donato Pompo says:

      I haven’t heard of this problem before, but it might be due to how the tile was installed over the ditra floor heat uncoupling membrane. Perhaps the spots that darken are conducting more heat there because of how the thinset adhesive was applied? Or maybe it is the reverse of that? Maybe there are voids under the spots that have darken? Or maybe the marble that is made up of many different minerals that those dark spots are a reflection of the content of the marble in those spots?

      The only way to determine for sure is to perform a forensic investigation to look for evidence of what is different from the spots that darken and those that do not.

      At this point I don’t think you can do anything about unless you wanted to spend the money and go to the inconvenience of doing intrusive testing. I doubt that the sealer will make a difference one way or the other.

  9. Peter Stone says:

    We have marble bathroom tiles and I noticed dark discoloring in an area on one side of the toilet. Can water have gotten under the tile to cause it? I can’t think of how else it would have discolored. It has darkened the affective areas.
    Can it be cleaned or dryer out

    • Donato Pompo says:

      The darkening of the marble next to the toilet could be from water or something else under the tile migrating up into the stone.

      You can use a moisture meter to see if the dark spot has a higher moisture reading. If there is a movement joint near by and a silicone sealant was used to fill the joint, and if there is a bituthene membrane near it, that can cause the bituthene to breakdown and migrate into the stone.

      Or the stain could be coming from the surface of the marble. Often near urinals stains can develop from water getting on the surface or from overspray by men using it. Marble can be refinished by honing and re-polishing it to see if that removes it. A poultice can be used too remove deeper stains that are difficult to remove.

  10. Andrea says:

    Hi,
    We just received a large delivery of grey and white marble squares to be used in the front hallway and kitchen floor. The boxes came soaking wet and a lot of the marble is dripping with water and mud. The order was thousands of dollars. The retailers said they had no room to receive the delivery in their warehouse, so instead left it outside for more than a month in the snow, rain, and mud. Some of the white marble is stained yellow on the sides and back. There are brown stains from the box in lines on the back of some as well. The shipment also smells. If we use this marble, will the stains show through from the sides and back? Will it be more prone to cracking because it was wet before sealed? Thank you

    • Donato Pompo says:

      First of all that was irresponsible of the marble supplier to leave it outside without protection against the rail and other conditions.

      True marble is very dense with an absorption of at least 0.2%. There are some stones sold as marbles that may have a higher absorption. 0.5% is considered impervious. So the marble shouldn’t absorb much.

      I have seen with some more porous tiles that the wet cardboard causes the water to stain that is absorbed by the tile. Then when the tile is later installed with the wet thinset and grout the stain comes out. Since the marble doesn’t absorb much that may or may not be a concern.

      Marble is known to have iron sulfide minerals, which when subjected to moisture can cause a yellow stain. If the stain is on the surface of the marble it might be able to clean it off. Although deep yellow stains can be hard if not impossible to remove.

      I would not expect the wet conditions to give the marble a propensity to crack.

      • Andrea says:

        Hi! Thank you for your help. Would the rust in the tile spread as time goes on throughout the tile? We noticed that some of the tiles that weren’t even yellow have started to have orange lines running now through the top. We are trying to get the order replaced but we are having a hard time. I don’t want to install tile that will have to be removed in a year. Thank you!

        • Donato Pompo says:

          If the marble tiles have stains and continue to increase, then I would not use this stone if you can return it. Otherwise you take the risk that it won’t come clean or will continue to develop more staining.

  11. Nowshad says:

    hi Donato,
    im planing to install indian white marble on floor white colour, its required any waterproofing material to be applied behind one side of marble?

    waiting your valuable reply
    thank you

    • Donato Pompo says:

      If the marble is being installed in an interior dry area, you don’t need a waterproof membrane. If there is a potential for shrinkage cracking (not structural cracking where one side of the crack is higher or lower than the other) then you should install a crack isolation membranes, which are also waterproof membranes if installed appropriately.

      If you are installing in a shower or exterior area that will be subjected to moisture, then you should install a waterproof membrane over the substrate to which the marble will be adhered to. This will help prevent efflorescence staining and spalling on the stone surface.

  12. Carlos Wheelock says:

    Hi Donato, I recently installed Calacatta cremo on my shower walls. Beautiful white stone with some gray veining and ocassional gold veins. But once installed, the white became more gray and the gold became more cream colored. The tile guy says its because the water in the thinset penetrates the stone and changes its color, but will dry out. But its been 3-4 days already. Will the stone eventually change color to its original white? The AC is not on because it is a new build and were in houston with like 80+ percent humidity.

    • Donato Pompo says:

      True Marble is very dense and low absorbing. Per ASTM C503 it can’t have more absorption that 0.2% which is technically impervious. So it isn’t likely to absorb water to cause it to darken.

      Some marbles are semi-translucent and that is why it is always recommended to use a white thin-set mortar to adhere the stone. If you use a grey thin-set mortar it can cause the semi-translucent stone to darken or give it more of a whitish-grey look. So if the installer used a gray thin-set that might have caused it to change in color. Not much you can do about it if that is the case.

      80% is a lot of humidity. Give it another week and see what happens. Add a fan in the shower to help dry it out. If it doesn’t lighten up then you know it isn’t due to moisture.

      The only way to fully determine what has caused it is to do a forensic investigation by removing some stones, but it may not be practical to spend for that service.

  13. Andrea says:

    Hi Donato,
    We installed a new shipment in the end of the grey and white marble and sealed it with grout release. We noticed that it seems to scratch so easily, for example we see tiny scratches even from the broom or from a cardboard box. Is this normal or is there something else we should be sealing it with? Thank you!

    • Donato Pompo says:

      Depending on the marble the physical properties of the stone can vary substantially. Marble is a calcium carbonate material and is very dense, although it tends to be sensitive to some chemicals and is easier to scratch than other stones like granite.

      There are products that can be applied to the marble surface such as Scotchgard™ Stone Floor Protector that will harden the surface and protect the marble polish. It has to be burnished on with a commercial buffer. It is best to hire a stone restoration company to apply and burnish the marble floor.

  14. Jj says:

    I had Carrera marble floors installed and i noticed a water spot but then went away. I asked the contractor to seal it in which they said they did but I tested the floor out by leaving a drop of water on it and it formed a spot again but went away. Is it safe to assume it’s not sealed?

    • Donato Pompo says:

      The way to verify that the marble tile is sealed is to apply a dime size drop of water on the tile surface. The water drop beads up with a tight meniscus then that is an indication it is sealed. If you wipe up the spot of water right away and there is no residual darken wet spot that further verifies the tile is sealed.

      If you leave a drop of water on any surface and the water evaporates it will leave residuals on the surface. A sealed surface will allow it to be cleaned easier.

  15. Khadijah Ward says:

    Hi, i am really upset, I have just had marble tiles ( carrara ) laid on my hallway floor and white diagonal lines have appeared throughout the floor. It does not look good at all. What is the cause of it and will it go away? Thank you.

    • Donato Pompo says:

      Your description does not provide enough information to determine what the condition of the marble is. The only way to determine if the condition is caused by the natural marble or caused by how it was installed and with what products is to have a stone expert forensically remove tiles to look for the evidence of what may be causing it. It is possible to remove a piece of stone and have it evaluated in a testing laboratory, which can be done. Although it might not be practical to spend the money to determine what is causing the problem, as it would cost several thousands of dollars to investigate. To learn about CTaSC’s forensic services visit https://ctasc.com/ctasc-services/forensic-failure-investigations/

  16. Marianne says:

    HI, I just had white marble with blue veining installed in my kitchen counter, island and backsplash. After the installers left, I noticed water like spots on the marble that were not there when I picked out the marble. The stains appear on all the slabs, and the finish is not as shiny as expected. My kitchen is under construction, so I have not put anything on them , and I have not had water in my kitchen for months, so they came like this. I have a call into the fabricator.. but what do I want them to do? They had to have seen it when they were here, but when they were here to install the backsplash..they arrived at 2PM and didn’t leave until 7PM . They did not say anything. I was going to have additional sealing put on, but when I found ou it was an additional 5K. I decided not to do that. I love the marble, but worry how it will look down the road. Thank you for you help. All your comments are helpful !

    • Donato Pompo says:

      Water spots, if that is what they are, should come off with normal cleaning. Sometimes they are etched spots which is when they are subjected to something acidic or highly alkaline. For instance if some beverage with residuals spilled on the glass and it sits for awhile on the stone surface it could etch it, which is a chemical alteration.

      The marble slabs can normally be further polished with the slabs installed on countertops. It might just need some additional buffing.

      Marble is questionable for kitchen countertops because they will be subjected to all sorts of chemicals from food preparation. Marble is primarily made of either calcium carbonate or dolomite (calcium magnesium carbonate) so that makes them chemical sensitive and scratch sensitive. Marble is actually very dense with an absorption of 0.2% or less.

      You can seal marble that will make them more stain resistant buy you have to reapply every so often. If a drop of water doesn’t bead up off the surface, versus spreading out, then it needs sealing. Sealers do not make the stone stain proof. If you spill something on the surface you need to clean it up promptly and clean it with the appropriate cleaner (do not try to clean up an oil spill with water) or the residuals can cause staining.

      $5k for sealing is excessive unless they were going to coat the marble with some sort of resin. A pint of marble sealer go along ways on sealing a marble since it doesn’t absorb and that should cost less than $100. That is why after sealing be sure to immediately buff it dry with a lint free cloth.

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