Cleaning Patio Limestone from mildew

My LARGE patio was paved with irregular pieces of limestone about 3 years ago. At the time the surface was sealed by the contractor (now out of business) with a glossy sealant (I don't know the brand). I can still see the gloss on the stone. The surface is a little uneven and water stands in certain areas after rain or plant watering. What looks to me like mildew (very dark green or black spots) has appeared in those wet areas. What do you recommend to remove the "mildew" (if that is what it is) from the stone?

 

Dear Steve:

When it looks like mildew it is usually mildew. It couldn't be anything else anyway.

A light power-washing with a specialty product to remove mildew stain rated for natural stone like Mb-9 will take care of that effortlessly. Spray it on and let it sit there until the stains disappear. It may take up to 10 minutes. Feed some product if it dries. Repeat in the most stubborn areas if necessary.

Rinse thoroughly when done.

May I ask you now to please read and e-sign our Statement of Purpose at: http://www.marblecleaning.org/purpose.htm?

Ciao and good luck,

Maurizio Bertoli

 

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