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 [log in to unmask] Dummerston, VT -- To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>