Problems with cracked and blown rendering

[dan007]

hi been plastering and rendering a few years lately having a problem with render blowing cracking and sometimes top coat appears weak ie easily marked when ladders leant against them i always soak walls first with water use washed plastering sand 4 sand 1 cement use addmixture everbuild 3 in 1 premium waterproofer plasticiser to slow down setting time then soak the scratch coat then apply top coat with 5 sand 1 cement again with add mix as above then float wall and sponge granted last job was on relatively hot day and sun was on wall all afternoon please advise