What is causing the white spots on this slate?

[boazcan]

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[J Scott W]

I would suspect moisture trapped under a finish or sealer. USe an air mover or a hair dryer blowing across the surface (not down into the stone) and see if this corrects the situation.

 

[John Olson]

agree with scott slate is void of calcium so it isn't efflorescence nor is it etching from acid since it doesn't have calcium.

 

[Mikey P]

Efflorescence from the thinset below

Where are those tiles installed?

 

[boazcan]

Back patio of condo 2nd floor water side.

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[boazcan]

I didn't take a closeup of the spot after, but here it is after dry treat enhancer.

You can barely see it left side near sliders about middle of the pic.

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[Mikey P]

Go back in a month (or less) and take notice..


Like I guessed before, thinset minerals...

 

[Mikey P]

Go back in a month (or less) and take notice..


Like I guessed before, thinset minerals...