In article ,
(Lobster) writes:

Wickes (in their Good Ideas Leaflet no. 12 at
http://www.wickes.co.uk/scat/goodideas )
advocate the addition of plasticiser to standard mortar to get the
benefit of lime mortar; ie making it not too rigid or hard. Anyone
had experience of this or care to comment?

I always use it when I'm not using lime. However, not everyone
is convinced it's a good idea.

I always use waterproofer too, with either lime or plasticiser.
(Sometimes I use all 3 if I only have a combined
plasticiser/waterproofer and want to use cement/lime mortar mix.)

--
Andrew Gabriel