This is what happens when a wall has been badly rendered! The render cracks, the rain penetrates and the house gets damp!
How to re render the wall: remove the old render (enduit). For this wall, it came off in a few pieces!
To make the render ‘enduit à la chaux’ mix some lime, sand and water in a concrete mixer. Apply 3 layers on the wall waiting 1 to 3 weeks between each layer depending on the weather conditions.
This lime render can be used on stone walls (pierre) or cob walls (terre).
You can also buy some ready mix (bags of lime and sand) from local DIY shops in France, all you need is to add water and mix.