if i use hydrated lime in my mix for exterior rendering to give me more time to work with it , assuming i use a mix of 4.1.1 , how do i integrate the lime ... do i mix it with water first and leave for a number of days or do i just shovel it in to the mixer with the s and c ... or is it easier just to use a retarder [i dont mean the labourer ;D]also on this job the original scratch coat is still intact ,how will i prep it for the top coat .. will i need to re- key [with an angle grinder ] and what about suction . will i need to apply liberal amounts of pva .. many thanks