Why is my limestone still staining after I sealed it?

QUESTION

My Ludders Limestone (outdoor kitchen) is staining after I applied a Behr waterproofing sealant (for stone) I am still getting stains from honeydew dropping from the tree s. Please advise.

ANSWER

ANSWER - Ludders Limestone is a Texas Limestone.  The absorption rate and propensity to stain does vary depending on the physical properties of the stone.  Per ASTM C568 limestone can be rated as a low density limestone, a medium density limestone or a high density limestone.  So the high density stones are lower absorbing and more resistant to staining.  I think the Texas Limestones tend to be medium density or low density.

Sealers do help make the stone more stain resistant, but not stain proof.  If some stain agent gets on the stone and it isn't cleaned up right away, it can seep through the sealer and stain the stone.  Also sealers don't last all that long.  Typically out door stones need to be reapplied every 6 months or so.  If you put a quarter size drop of water on the stone and if the drop of water doesn't tightly bead up and if it leaves a damp spot after you wipe it off then the sealer isn't working and you need to reapply.

To clean deep stains you can use poultices to draw them out.

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