Should have spotted this earlier instead of posts from 2006.
If you have timber, building paper over it and then mesh at least 100mm around it, fixing mesh to blockwork so that timber can move independently underneath it.
If you have a pier, column, long expanse of wall, straight vertical joint, vertical crack , you may consider a movement joint . This will be a back to back stop bead or integral expansion bead.
If you have 'general ' cracking where you cant explain movement , mesh over it , at least 100mm each side .
It is standard practice in monocouch to mesh around stress points like windows & doors . A 500mm band, overlapping where vertical and horizontal meet with fibre galss mesh is usual (lapping beads slightly). Sometimes the whole elevation is meshed.
Stainless steel mesh must be used outside if metal. If you mix staainles and galvansied eml, you can have an electrolytic reaction causing breakdown -but I have never seen this in practice actually happen.
Fibre glass meash is more flexible, , youcan cover it with less gear and it is easier to cut to size/length etc.
For the ideal meshing, use fibreglass mesh, lapped 100mm and dropped vertically. Bed into rendaid, hpx , s&c sbr or waterproof or lime scratch coat or similar and give it a key (with any timer betc as above)
This will keep cracking behind the render , which can move or carck at joints, it will stabilise background and minimise cracking.
However - it is not magic -if there is enough movement, you will get cracks - that is why you try to get it to 'crack'where you want it -hence 'control joints' as a term for movement or expansion joints.
There's more I;m sure .......