How do you remove stains in Limestone in an Exterior Application?


customers just installed lime stone slabs and walls outside there newly constructed home.

there are many rust looking or brown muddy looking spots in various places. How do we remove this or is it something that will keep recurring. there is about 7000 sq ft of slabs walls and benches .

Please give me your suggestion, customer has spent over $150 ,000 of limestone in there back yard . there not happy seeing these stains

I look forward to your reply.


ANSWER - Limestone stone is a calcium carbonate sedimentary natural stone.  It contains various minerals such as ferrous oxide that when subjected to excessive moisture can develop mineral stains.

Sometimes this is just minor staining that can occur.  If the stone wasn't installed correctly and it is being subjected to excessive moisture it can develop excessive staining.

Some of these stains can be removed, but will return if they continue to be subjected to excessive moisture.   You can experiment with different poultices to see if the stains can be removed.  You should hire an experienced profession store restoration company to attempt to remove the stains.

Sealing the stone can help minimize the staining if the moisture is coming from the surface, but won't help if the source of the water is from below the stone.

8 thoughts on “How do you remove stains in Limestone in an Exterior Application?

  1. Ajay Jari says:

    I recently resurfaced a French limestone balcony floor and sealed it with lithofin solvent based penetrative sealer. Because the stone has already had water damage, browning and spalling the underlying moisture keeps rising to the surface bringing along with it a residual haze of lime, salt and acrylic type residue. Any advise please

    • Donato Pompo says:

      The problem likely is you are trying to treat the symptom of the problem rather than the problem.

      We have been on a many cases like this. Chances are the problem is in the underlying assembly. Often the waterproofing is applied under the mortar bed and may not be sloped or may not be sloped adequately to a drain so it can evacuate. We always put the waterproofing on the sloped mortar bed that we then adhere the tile to.

      Thus the underlying mortar bed becomes a reservoir of water that never dries. Thus the water migrates to the stone surface it precipitates the minerals it picked up along the way leaving the efflorescence staining and spalling.

      An unconventional remediation that can work under certain circumstances, particularly if the stone is very low absorbing, is to cut out the grout joints to a 1/8″ width or wider. After cleaning and drying fill with a traffic grade ASTM C920 sealant. This in theory will make the joint watertight, (assume that is how the water is getting below the tile, and it will provide added movement joints to mitigate various movement stresses.

  2. Robert Corrado says:

    Hello Donato Pompo. My 15-year-old beige limestone porch is so badly stained by rust and mold. I tried every cleaner on the market. I even tried muriatic acid. Still doesn’t clean it. Before pulling the trigger and replacing it. What about using a mason stain on it?

    • Donato Pompo says:

      There are 3 geological classifications of limestone. A class 1 Low Density Limestone is very porous, the Class II Medium Density is less porous, and the Class III High Density limestone is the least porous with a maximum allowable porosity of 3%. The more porous the greater tendency the limestone will stain.

      In theory, you can restore limestone by grinding it and rehoning it to the finish you prefer. This might remove the surface stains. If you have a porous limestone the stains may go deeper. There are stone poultices that you can use to help draw out stains, but it depends on the types of stains you have.

      If it fits your budget, you should hire an experienced and quality stone restoration to refinish the stone and to reseal it so it looks almost like new.

  3. matt b says:

    what is the best alternative to limestone that gives the same look, but doesn’t suffer from the awful staining? It seems pre-cast is even worse (all of the mouldings and exterior trim in my neighbourhood looks very beat).

    • Donato Pompo says:

      If you want a tile that requires less maintenance and is more durable and resistant to various conditions that affect natural limestone, then you should select a ceramic porcelain tile with a limestone look created with an Ink Jet technology.

      Quality produced tiles in this category give a very realistic appearance and can provide variation in the appearance that can be similar to the respective limestone look. There are many different types of limestone with different looks.

      Porcelain tiles are impervious and requires a lot less maintenance than natural stone. Although porcelain tiles are very durable they can chip if abused, which can’t be repaired where it isn’t noticeable. Natural stone requires a lot more maintenance and is less forgiving to various types of conditions that would cause problems with certain types of limestone, but if you chip a limestone or etch it, it can be re-ground and polished to look like new for a price… Natural stone does have some intrinsic value in that it is nature made and millions of years old…

  4. Brad Cox says:

    I have a 2 yr. old limestone patio (4,000 sq.ft.). Last winter a few pieces started pitting and spalling. This year over 100 are doing this. The cost of this patio was in excess of $175K. I went out of state to get Prosoco Natural Stone sealer VOC but haven’t applied it yet, because I’m not sure if this will make things worse. The patio that is covered isn’t having this problem so it seems to be water caused. Before I replace all the stone thats damaged, i need to know how to stopr it from dooing this again (so I don’t waste $75K in repairs). US Stone has agreed to send me replacement stone for free because we spent in excess of $300 with them on this project. Any advice is appreciated. I’m also happy to hire you to review this case.

    • Donato Pompo says:

      Generally speaking when there is a failure it is never due to a single deficiency, but rather due to multiple compounding deficiencies. Normally when there is excessive spalling in limestone it is due to the limestone being subjected to excessive moisture. This is often due to how the tile was installed both from a design point of view as well as from an installer point of view. If there isn’t adequate provisions for drainage or if the substrate is configured and designed where it retains moisture this can cause the excessive moisture condition. Another factor is what is the physical properties of the limestone. Limestones with lower physical properties can make the stone have a greater propensity to damage than a limestone with better physical properties. The geological classification of limestone allows for 3 different classes of limestone from lower to better physical properties.

      The spalling of the stone is the symptom of an underlying problem. So just treating the symptom will not prevent the problem from reoccurring. So you have to remove some tiles under various conditions to identify the deficiencies. Once you have identified the problem then you can determine how best to remediate it. It might be necessary to perform laboratory testing to evaluate the physical properties of the limestone to determine if it has contributed to the problem.

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