Although I have found a number of hits for 'finishing mortars', 'renders' seem to be what you need.

http://www.ceresit.com/Renders-mortars.19742.0.html

Cover (stone or brick) with a coat of plaster:
external walls will be rendered and tiled

http://www.oxforddictionaries.com/definition/english/render

External lime renders were traditionally applied to both disguise and protect walls built of poor quality material such as rubble stone or porous brick and rough timber. They were usually covered with a colour wash or limewash which also provided additional protection.

http://www.minervaconservation.com/articles/externallimerend...

Lime renders were traditionally applied to give protection to walls built of poor quality rubble stone or porous brick or to walls in exposed locations facing driving winds. They help by acting like a sponge, absorbing rainfall then allowing it to evaporate rather than soak into the wall. Most cottages and houses built of rubble stone would have been rendered originally and they tend to suffer from penetrating damp if the lime render is removed or replaced with a cement rich render.

http://www.periodproperty.co.uk/shop/acatalog/plastering_wit...

Plaster and render are mortar coatings that cover blockwork. The coatings on inside walls are called plaster, while the coatings on external walls are called render.

http://www.ratedpeople.com/c/advice/trade-insights/insights-...

The Baumit range of lime renders are high quality products which have been tried and tested for many years to the highest standards. They are ISO 9001 certified and have European Technical Approval (ETA). Baumit are the European leaders in lime based breathable renders.

http://www.limetechnology.co.uk/render.htm