Many buildings South Wales are famous, in the construction world, for their black mortars. Many a householder has drilled into Victorian walls to find a fine cloud of black dust emanating from the hole. People replastering and rendering walls have had to cope with cleaning up a layer of black ash from their homes.
This has caused black mortar to get a bit of a bad name, however its history is based in the mining and manufacturing base of this area. In order to make a good mortar you need to have a fine aggregate and what finer, and cheaper, aggregate than the dust and ash from the industry abundant in the area at the time. This ash was mixed up with lime putty to make a mortar and render mix that was strong enough to the service the construction industry of the time. So these old black mortars are a rich reminder of the industrial heritage of the South Wales region.
However, lime mortars now come in a base white / off white colour. Lime putty mortars mixed with a limestone aggregate are certainly too pale for repointing. Some companies will match colours for you, but then you are at the behest of the type of aggregate that you are offered etc. This is also an expensive option when looking at doing small areas of re-pointing.
So we would recommend the following solution:
Buy the right mortar (lime putty with limestone dust aggregate)
Buy a lime tolerant black pigment (earthborn do one of these available through our E-Shop)
Mix the pigment with some water and then knock up the mortar and pigment to get the right shade.
Happy Black Re-Pointing!