rendering over render

[bignorm]

Hi, i need a bit of advice on re-rendering the back wall of my house.
What i have at the moment is a smooth painted render that has failed and is letting in damp.
I would rather not hack it all off as it is the original with sharp sand and is like concrete.
Would i be able to key it up and then put a one coat pre-mixed render on?
If so, what would be the best product for this and the best way to go about it?
Regards

 

[Alastairreid]

hack off any loose render first then fill level with existing, score the surface with a grinder/stihl saw

pressure wash, apply stabalising solution,stop/bellcast beads then render......info here