Here is an example of the type of damage that can take place when a soft stone wall is pointed with cement.
This is a south facing elevation of a house in Longwell Green, Bristol.
The soft stone of the house has been eroded away because the hard cement pointing does not encourage moisture to evaporate through the mortar. The result is that moisture has been trapped inside the solid constructed wall, leading to dampness. The only way that the moisture can escape is through the stone itself. This has led to frost damage over a period of time and is always worse lower down the wall. This is due to rising moisture and no damp proof course (dpc).
Hard Cement Pointing damage to soft stone
This a view of the west elevation of the the same Longwell Green property. West walls are more exposed to the weather and as a result, the walls soak up more rain and are subject to greater erosion.
If the hard cement is allowed to remain, this wall may suffer potentially catastrophic damage.
The stonework has been so badly damaged that rendering is the only course of action. This is explained in our repair guidesheets, we also instruct people in the use of lime on our use of lime in renovation course.
Photos reproduced with kind permission of Alan Arnstein