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


> >     (ruling out historically tinted mortars)
> >
> > When 19th century builders colored the mortar to bring out colors in 
> > the surrounding masonry, did they color the entire batch?     Or is it 
> > only the first inch or two?
> >
> c,
> 
... was tinted through and 
> through. My feeling is that this was the prevalent trade practice. But 
> I have also seen evidence of walls built with an untinted mortar then 
> followed up with a tinted top pointing. It would likely be work where 
> more expense and care was intended and les focused on optimal 
> production in the building process. So there is no exact yes-no answer 
> to your question. As our esteemed Mr. Edision has pointed out one 
> needs to look at the forensic evidence of the structure. Problem is 
> getting to see into the wall, which is where probes come in handy.
> 
> FYI there is a point where the percentage of tint to mortar begins to 
> have what is considered an adverse effect on the strength of the 
> mortar. I do not remember where that point is at... seem to remember 
> people arguing over if it as 10% or 15%. For the most part I don't 
> need to worry about it. As to mortar analysis I suspect that it is 
> nearly impossible, certainly impractical, to determine what the 
> proportion of tint is within an existing mortar. When one wants to 
> match to an existing color of tinted mortar it is partly through trial 
> and error, science and art. Note that I did not include bull crap in 
> that recipe.
> 
> ][<

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