A well-built rubble masonry wall is unlikely to need repointing for at least 100 years. If repointed properly, it should then last another 100 years without much further maintenance.
Repointing is necessary when the bedding or jointing mortar washes out and the stones start to become loose and at risk of falling out of place. It may also be necessary to halt the damaging effects of cement mortars, one of the common causes of problems with rubble pointing.
Lime mortars should be used for masonry repointing as they let the walls breathe. Careful mortar preparation is important, as is the thorough raking out of decayed mortar from the wall to make a sound base for the new mortar.
Care must be taken to replace missing pinnings (small stones) that have fallen out from between large stones. This should be done during the tamping stage to preserve both the wall’s structural strength and its appearance.
Detailed photographs should be taken before work begins of any sections to be dismantled and rebuilt. These provide a reference against which you can compare the finish and quality of new pointing with that of the original wall.
Characteristics of rubble masonry