LimeLike Dark Ash & applying Dyebrick Charcoal stain to produce grey brick and mortar.

LimeLike 'Dark Ash' applied to red brick. Then Dyebrick 'Charcoal' brick stain was applied afterwards to produce a multi-shade grey brick.
The Dyebrick 'Charcoal' was diluted three times.
Please try samples first to ensure how it works on your particular brick type.