Do not let the vinegar sit on the flagstone for very long as the acid can damage the stone. The vinegar is used to kill the mold spores to prevent it from returning.

Is vinegar safe on flagstone?

The best way to clean flagstone patio is with flagstone cleaner. It won't stain or erode your stone and mortar. Don't be afraid to clean flagstone with white vinegar diluted in equal parts of water. Cleaning flagstone with bleach is safe when following the usage directions printed on the label.

What can I use to clean flagstone?

Mix together equal parts white vinegar and warm water. Make sure you do not use apple cider vinegar, balsamic vinegar or any other variety that is not clear, as they can stain your flagstones. Spray your flagstones with the vinegar and water solution, being careful not to soak any nearby vegetation.