It is generally black and they use it after they pore the concrete and apply it before it sets. they generally trowel or helicopter it in to the wet concrete.

It seals the concrete, because it is such a fine powder it fills the gaps and makes concrete less porous, therefore it is good for Garages and carports making oil leaks easier to clean off. Generally only the top 6 - 8 mm or so is protected by the granilite.
On some big jobs they add the powder to the mixer so that the whole mix has granilited in the powder..like a science lab, where they want greater porosity protection.

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Note added at 2 days10 hrs (2010-05-08 06:04:20 GMT)
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Here is the latest fad instead of tiling concrete they stamp it using granulated mixed concrete.

http://www.google.com/images?client=gmail&rls=gm&q=Concrete ...