i have been a builder for 22 years and have worked in an assortment of situations, so, i believe i know what i am talking about legs so please dont assume i dont know what i am talking about when its obviously just a difference of opinion
when you are rendering use a waterproofer for the scratch coat and lime for the finish coat. the waterproofer also improves the workability of the mix. if the area is large though i would get a tradesman in