Why did my Indian Sandstone slabs turn yellow and what can we do about it?


We have a problem in Indian sandstone where we had slabs placed upright in a concrete base. 3 Weeks after installation they started to become yellow.

After 4 months they were treated with an acidic solution which resulted immediately in the original grey color but only a week later they started to become yellow again.

If we remove the gravel near the base we see that parts that had been covered still are in the original grey. The geology in the region is rather clay so that is not an indicator for this problem as we sold lots of these slabs in the region. See attached photos. What is causing it and what can we do about it?


ANSWER - Wow that looks pretty extreme.

Considering you could clean it off suggests that the staining is originating on the surface versus within.

Considering the covered based has not discolored further suggests that the staining is originating on the surface versus within.

This type of staining normally means it is being subjected to moisture, which perpetuates staining of this type when the moisture comes into contact with iron oxides.  Limonite, an iron ore, that is found in some quartz stones that yields yellow, brown and buff shades of color.

It is known that with quartz based stones that oxidation of the iron minerals within it can cause some stones to change color after installation.

So your stone may contain Limonite containing iron minerals that when subjected to moisture from rain, condensation, or sprinklers is causing this staining to occur.

Maybe be if you clean it and then seal it with a surface type sealer it will prevent or retard it from occurring?

4 thoughts on “Why did my Indian Sandstone slabs turn yellow and what can we do about it?

  1. Darlene Hamilton says:

    A Gray sandstone was installed over concrete slab in Late fall 2021. It looks as if cleaned with muractic acid, but denied by installer but is very rust and brown now. Is there a remedy? Could there be another reason for discoloration?

    • Donato Pompo says:

      They should have never used muriatic acid as it is too corrosive. It does tend to give a yellow cast, so maybe it caused the discoloration.

      The question is if the stone is stained only on the tile surface or does it penetrate into the sandstone a ways? Sandstone can be very porous. If it is a surface stain, in theory you can grind the surface down to remove it. Or maybe you can power wash it. Sandstone is a cleft material so it tends to cleave, so to maintain that look you might need to chisel the surface rather than grind it; just depends on the type of sandstone it is. You should hire an experienced stone restoration company and see if they can do some testing to determine how best to restore the stone. Always test a small area before proceeding to make sure you are satisfied with the results.

    • Donato Pompo says:

      Flagstone is a shape of a stone that is very irregular facial dimensions and in thickness. Often it is a sandstone or blue stone or could be another geological classification of stone. In theory you can grind or sand blast a stone since it is the same material throughout. If you sand blast it will cause the tile to have a texture that will change the natural clef look. Depending the type of stone and its physical properties sand blasting it will give different results that may or may not be desirable. Test a small piece or area to make sure the results are acceptable before applying to the entire area.

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