There are a number of visual signs that can be seen when brick and stone masonry structures require restoration.
Restoration of an existing stone or brick structure may just require changing a couple of masonry units that have been harmed by unexpected blunt force effects that need grinding out the mortar surrounding the harmed units, removing the harmed units and re-pointing them back into place with a coordinating mortar.
Why require restoration procedures
There are times when more serious restoration procedures need to be carried out when parts of a masonry structure start to show staining, brick face spalling (splitting and cracking), mortar fractures and collapsing. These are indications that the masonry structure is under siege from the components from the within and the product of the wall starts to break down. This kind of damage is typically brought on by wetness entering the brick or stone face structure and gets caught there.
When freezing and thawing takes place, the product broadens and contracts at different rates, triggering a breakdown in all of the product, brick and mortar alike. This reason for this type of degeneration needs to be visited finding the source of the dripped wetness, whether it be a dripping wall flashing or wall cap and so on.
Once the wetness leakage is found and stopped, then there are a number of ways to approach the repair or restoration depending upon the degree of the damage. If the level of the damage is big enough, long times you would be much better served (expense and time smart) to simply change the whole wall or structure.
There are also circumstances when the structure or the footer of the masonry wall is the reason for masonry wall failure.
When an unsteady structure or structural failure is at fault, you will see the mortar on a brick or stone structure start to retreat or separate from the brick or stone units, leaving spaces in between the mortar and the masonry units in a horizontal stair action pattern. There can also exist, periodic vertical fractures in the mortar and often even in the brick units themselves. The structure will need to be fixed before any efficient restoration can occur.
Another note: if you are planning to have new outside hard-scape work done such as, free-standing masonry walls, fireplace, outside entertainment areas and maintaining masonry walls, you should (should) have a correctly put, re-bar strengthened, concrete footer beneath the masonry structure, to have a sound, lasting masonry component.
The first thing you ought to do is completely clean the surface with a soft acid wash and a pressure washer. You should take care not to contribute to much acid to your option to ensure you do not harm the brick or stone. You need to then scrub with a firm bristle scrub brush to remove all the loose dirt. If you are knowledgeable with a pressure washer this would also work, you simply need to be really careful not to harm the surface with the high-pressure water stream.
Doing the entire surface will ensure a quality job that matches completely and chances are anyways you will have to ultimately tuckpoint the other areas also even more down the road anyways.