The solid walls so common in Wales are prone to damp after the ‘modernisation’ they have received over the past hundred years. The addition of external cement renders especially has locked moisture into the walls and the remedial work of injecting damp proof courses just doesn’t work. I have covered this point on numerous occasions in previous posts. I might be getting obsessed!
So the scenario posed here is having an issue with rising damp with an external cement render. So how to cure this problem in a quick and relatively easy way?
The best thing is to remove the offending cement render to allow the wall to breathe. In order to achieve this at lower levels (assuming that the upper levels of render are sound – no hairline cracks etc) you can cut a straight line in the render using an angle grinder. The lower render can then be knocked off using a hammer and bolster – it may well come off relatively easily as it has probably ‘blown’ away from the wall. Unfortunately this process may well take off the glazed surface of the bricks. So in order to create a finished surface we would recommend applying three or four coats of lime wash.
Limewash is really breathable / porous. This has two advantages for us:
1. It will help to suck out the moisture from the walls on drying days (these are effectively any day where is it dry, windy or with light rain)
2. On heavy rainfall days it will help to keep the wall dry. Basically the limewash gets saturated with the rain and then it sheds the excess rainwater off of the surface
This gradient of porosity / breathability is the key to a successful wall. The inner finish should be between 3 and 6 times less porous than the external finish. The internal pressure and breathability gradients then encourage any moisture in the walls to the external surface where they can be dried by the weather.
Ultimately if you want a render finish again on the external wall, then look to render it with a lime putty stone dust render topped off with the limewash again. Note that the limewash and putty should be ‘hard’ lime putty that comes from limestone rather than the ‘soft’ putty from chalk.