Our converted barn granite wall was repointed with lime mortar last summer as it gets very damp on the inside during the winter, the wall faces the prevailing wind and rain. The inside has been rendered with normal concrete, I understand it will take some time to dry out but it is still very damp on the inside. How long will it take to dry out and is there anything I can do to help, should I put some kind of waterproofer on the outside or will that stop it from breathing.
The wall will take some time to dry out, however if it faces the elements there is a chance that the wall will possibly take in more water/moisture than it can release at a given time, especially during periods of heavy rain and wind. If you were looking to coat the outside we would only recommend using the Beeck S P Plus as this acts as a breathable water repellent, we have both real life and test data that proves it does not impact the vapour permeability of the wall, but should reduce water ingress by up to 95%.
The second issue you may be experiencing is the internal finish of the wall, as it is rendered with a cement/concrete this will hold moisture captive within the wall and allow it to build up. Whilst the lime mortar externally will allow moisture to be released, as the moisture if forced into the wall through wind driven rain it will naturally work itself inwards (as the internal climate is warmer). A possible alternative is to render the internal with a lime plaster to allow moisture free passage and escape at both ends, preventing it from being held within the wall.
If you would like to discuss the problems and potential solutions in more detail please give us a call on 01208 79779.