When it comes to dealing with dampness in solid wall homes an investigation should first be made into the underlying cause. If the root cause is either penetrating dampness through porous wall surfaces or condensation damp then an external thermal cladding can be used to clear the problem with the below caveats . If the problem is rising damp then a Damp Proof Injection Course will be needed before any exterior cladding is applied.
Breathable External Insulation
Once the reason for the damp in the walls has been identified then if exterior insulation is appropriate the trick is to use a water vapour permeable insulation board and in this case either a mineral wool or phenolic board is most suited with an EPS polystyrene board being discounted.
Having removed any wet render or paint from the wall and allowed the walls to dry out for a short period the insulation cladding can be affixed without fear of trapping any moisture in the walls.
The insulation and the render coating are both microporous so will stop any more water penetrating into the underlying wall whilst allowing the dampness within the wall to escape naturally to the outside.
If the walls are cavity built and there is a pentrating damp problem then a specialist wall tie inspection firm should be called in to insert cameras into the cavity and see why the water is tracking across the cavity. This should be done before spending your hard earned money on external wall coating systems to solve what could be a structural problem.