So far I have tried the approach Jim SW described here http://www.rmweb.co.uk/community/index.php/topic/18906-painting-mortar/page__pid__182482__st__0&?do=findComment&comment=182482 which worked well some of the time, but also started removing the red paint.

I also tried just painting on a the mortar and then wiping off which was a bit tougher to remove (but avoided the paint stripping properties)

I did find that the deeper relief on the bricks compared with Slatters embossed brick made it a bit easier than when I was working on the brick buildings for the last layout.

Photos will eventually follow, but for the time being its not particually photogenic (as the back wall of the bridge has a lot of gaps where detail would have gone if I had a bit more patience