Mike,  Here's a question I have not thought of in over 35 yrs.  Why
were/are green cement blocks more expensive?  Way back when I was married
to a different fella we built a house using split face cement blocks.  I
orginally wanted green but they wanted ten cents a block more for green,
all other colors were one price.  We used brown instead.

We used brown mortar, it was brown all the way through, why mix up 2
batches just to make the inside and outside 2 different colors.  Don't know
whether it was natural or unnatural cement but the house is still standing.
I handled every block in that house at least twice and some more than that.
Ruth


At 2:40 PM -0400 4/15/07, Edison Coatings wrote:
>I suspect that tinting practices varied tremendously. On the American Museum
>of Natural History, outer pointing mortars were red, inner bedding mortars are
>grey. Of course, you know I'm not going to leave it at that...all the mortar
>is natural cement-based.
>
>As for maximum pigment levels, ASTM C979 (colorants for concrete) restricts
>iron oxide pigments to 10% of the weight of the CEMENT, not total mortar
>weight. Carbon black is restricted to 2% of cement weight. As the proportion
>of the very fine pigment particles increases, it takes more water to make the
>mix workable, and there is more surface area competing for the cement. High
>pigment levels therefore reduce strength and increase shrinkage. Most colors
>can be matched with 5% or less (on cement wt.), and increasing beyond this
>point doesn't necessarily give stronger colors- a saturation point is reached.
>
>Mortar analyses CAN identify original pigment concentration, which goes back
>to an old argument I had with a restoration architect who wanted to replicate
>the historic mortar on a building in Florida. Pigment concentration was over
>20% and I argued for a year that he should not duplicate a mistake. Reason
>eventually prevailed in that particular case.
>
>Mike E
-- 
Ruth Barton
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Dummerston, VT

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