Sand is the most abundant ingredient in the mix. The powdered cement and lime are the glue that holds the sand together and allows the mortar to bond to each brick (or concrete block, stone or other ...
Black particles might be biotite ... plus the cement/lime paste that you can see in between the particles of sand. Over time, the mortar joints between bricks in a wall, also known as pointing, will ...
Black particles might be biotite ... that you can see in between the particles of sand. Over time, the mortar joints between bricks in a wall, also known as pointing, will fail.