We have had a single storey extension built at the rear of our property - the side wall is only about 10" away from the neighbours extension. The side wall is constructed of breeze blocs - the rear of the house is in the process of being rendered but it is impossible to get to the side wall due to the narrow gap - therefore at the moment it is just plainbreeze block along this outside wall and not waterproofed.

The builder has suggested applying paint but even this will be difficult to do - any ideas?