Stuart Noble wrote:

How do you make black mortar then?

as lime mortar but some or all of the sand is replaced with ash. It was
forbidden on many building projects as it was more prone to failure
than lime mortar. In many cases it was used anyway on the non visible
areas, as coal ash was something one had to pay to get rid of.

If repointing patches of black mortar, the logical thing would be to
use more black mortar.


NT