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I had an additonal 12 by 8 slab poured right next to my original driveway. Most of the slab looks powder white but there are big blotches of gray. I don't know if I am using the right words to describe the colors I see but you get the idea. I dont know if my eyes are deceiving me but it looks like the gray blotches are slowly disappearing. Is this part of the curing process or what? Any thoughts? Southern Calif
 

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A picture would be nice.
Is this a new slab you just had pored?
 

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the slab was poured well over a year ago. I am looking for dated picture in my files. I apologize for no picture. I have tried loading them on here before with no luck. It is probably a me problem
 

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Calcium carbonate can leach out of cement products, and that could be the source of the white coloring. Calcium carbonate is water soluble and moves with the water coming out of the cement as it dries. When the water evaporates, the CC is left behind in the same process that creates cave formations.

If that is what the white residue is, than it can be washed off. Even plain water can remove some of it when it is fresh, or you can use a weak acid solution. There are commercial phosphoric acid preparations that are used for this purpose, but I would do a bit more research before going that route. You could try a little water and vinegar, or diluted CLR and see if that cleans off the white.

I would not expect this to still be happening over a year after the pour. How long after did you notice the color? If it happened right away and you just never got around to removing it, then you can probably just clean it off. If it happened later, that could imply that there is still water moving through the concrete, such as if the ground underneath is constantly wet. If that is the case, the white could come back, so the fix may be more complicated.

As far as uploading pictures, are you using any script blocking software with your browser? There are also size limits, so I usually have to open my pics in photoshop and re-save them at smaller size and lower resolution. Any resolution around 72dpi is fine for viewing on the web. I think you want to keep pics under 100K, but I don't remember.

LMHmedchem
 
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