What has caused my Blue Stone to show rust stains?


I recently had 'Blue Stone' Slate put in my backyard for a huge patio, we have not sealed it yet with a breathable sealer but have cleaned it, we are noticing yellow type rust color bleeding thru different areas but not all, the patio is not being hit by any sprinkler water , it kind of looks ok as it makes it look rustic but was wondering what would cause this bleeding of rust color in some areas
I could send a picture if needed


Questions -  Most stones contain some ferrous oxide minerals that when subjected to excessive moisture can cause a rust-like stain.   For it to occur the stone has to be subjected to some level of moisture. The moisture could be coming from the stone surface or from under the stone.

Sealing the stone with a proper breathable sealer can help prevent this from happening.  Depending on how the stone was installed, normally it  is recommended to seal the stone within a few days after it is installed; assuming that the stone assembly has substantially cured.

You can power wash the stone to help remove the rust stains.  You can also use poultices for removing stains.  You will have to test different methods to determine what will work the best.  After it is clean and dry, then seal the stone.

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