What are the Common Problems with external rendering ?

Drying too fast allowing cracks to form in newly applied render.The render not bonding to the surface underneath and parting company from the wall ,this may not be apparent for a couple of years after the render has been applied.The wrong mix used ie too much sand which makes the render more prone too weathering .A good render applied to a well prepared surface will give years of protection and if using modern finishes can keep maintenance down to a ten yearly cycle .The cheapest quote is not the best and perversely neither is the most expensive far more important is recommendations by friends and membership of trade organisations and to check those credentials