What is that White, Powdery Residue?

[robastewart]

Recently we moved into a house with hundreds of square feet of porch and patio laden with saltillo tile. Amazingly, much of the tile has never been sealed, and the house is 3 decades old. Advice is needed on two problems: (1) Several areas are stained by years of rain, snow, and dust storms, some of the stains appearing to be moldy or algae-like. (2) Some areas of the tile on the front and back porches emit a white, powdery substance, especially after it's been wet. What suggestions do you have for dealing with these problems before I attempt to seal the tile?

Much advance appreciation extended.
-RAS

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[ddmoit]

Welcome to the forum, Robert.

Check out this link...

http://johnbridge.com/efflorescence.htm

[robastewart]

Wow! Thanks for the great, informative link. It's as if the writer had been standing on my porch to inspire description. I will be investigating products to combat efflorescence.

Any info to point to regarding the stained or molded tile?

Much obliged.