Coloured mortar can be used as a decoration, and also to disguise the newness of repointed joints. To give a grey tone to the mortar. When working on a small area, rub dirt into the mix. If the area is large, use a vegetable dye. Obtainable from a builders’ merchant.
When using vegetable dyes, remember that the colour will be much lighter after the mix has dried than it was when it was first made up. To get the right colour, experiment with previously measured quantities of powder and mortar and allow them to dry-Then working in equal proportions, make up the full quantity.
When repointing part of a brick wall with coloured mortar, always rub the surrounding mortar joints with candlewax. This stops the existing joints soaking up the colour.