How to coat previously lime-washed walls

A large number of old buildings, particularly in rural areas, have been coated with lime-wash ( also referred to as white-wash). Restoration of these buildings is a complex affair and needs to be undertaken by a skilled contractor who is prepared to pay attention to detail.
The external walls of many of these structures can be anything up to 50cm thick, built without a cavity or damp-proof course. Lime-wash does not seal these walls, so in winter months the walls get very damp, but due to their thickness this moisture never reaches the interior. During summer months the walls dry out, and the lime-wash allows this moisture to permeate though it unchallenged. The paint coatings applied to the exterior of these walls has to be breathable i.e. they should allow moisture vapour to pass through them at a high rate. Matt coatings, with an excess of pigment over binder content, are suitable, and less expensive than the sheen coatings usually used on exterior walls.
Before coating, all lime-wash needs to be removed from the walls. This is best done by scraper and bristle brush as high pressure water-jetting is not an option on old clay brick walls. This is a tedious process, requiring a lot of patience and perseverance. Once all the lime-wash has been removed, and the inevitable repairs to the plaster have been completed and dried, apply one coat of an alkali resistant Plaster Primer and allow to dry overnight. This primed surface can then be top-coated with an interior-exterior matt finish paint such as MattCoat 40.