Cement render first became widely used just after the war.  Since then, it has become the ultimate decorative fad, and is touted by ignorant builders as the only way to keep a building dry - "Stop the water getting in dear - give it a good coat of cement render - that'll keep it dry"

Unfortunately, that's exactly the wrong thing to do.  Old houses are built with stone, soft brick or lime mortar - all of which move around quite a bit with heat and seasonal changes.  Cement doesnt - its rigid.. So it cracks - rapidly.  Then, because its non porous, it traps water.  So within a few months, you get a damp wall - this just gets worse and worse - as the wall gets wetter, it conducts more heat, so the house cools down.

Cement render on old houses is a complete No No... Cement render on an old house needs stripping off.  NEVER render an old house...   Phew.... think I've made that fairly clear to all readers now.  If a builder even starts to say it, sack the uneducated twit and find someone that talks about breathability.

The damp wallies will always use cement render as a means of 'proving' rising damp.  The wall is wet - so it must be rising.  No its not - remove the cement and it dries out.  No ifs, no buts - FACT.  And no rising damp.  It never was.

There is a huge problem looming - Externally Applied Insulation..

Under new government legislation, energy companies are being forced to encourage people to insulate their houses.  A raft of companies are springing up who claim to insulate your house externally with all sorts of cladding.  These are Certain Death to an old house and must be avoided at all costs - they are no better than cement render and are already causing huge problems.