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.

2 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.

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