Block walls (masonry walls), will often lean some and often has cracks as well. Tree roots and soils are generally the cause.
If there is a block wall in-between two neighbors in an area with expansive soils, and one neighbor waters their yard a lot, and the other doesn’t, there is tendency for the block wall to lean. Because expansive soils expand when they get wet; the side of the wall that has more water applied to it may push up on that side of the walls footing.
Block walls are often on property lines. If there is a difference in elevation, soil movement or incomplete compaction, then the wall may start to lean over time. Block walls are heavy and if placed on top of poorly compacted soils, then they tend to settle, lean or crack.
Tree roots and various types of shrubbery may push on the footing and cause the wall to tilt. When it appears that roots may be causing the wall to move; then cutting back the roots may help. Be careful that if the roots are from your neighbors tree, that you don’t kill his tree, for this may create legal issues.
A “Push Test”
If you push on a wall and it moves back and forth, or if it leans significantly, then consulting a block wall specialist would be wise. Two other factors to consider are; is there significant cracking in the wall and is there rebar and grouted cells in the wall?
Rebar, which is steel reinforcement, makes a wall stronger and reduces cracking. Older block walls may not have rebar in them and are more apt to crack or fail. When contractors place rebar in a wall, they will grout the block cells.
Masonry contractors are normally the type of contractors who repair block walls.
Who to consult? Masonry or concrete wall contractors.
The majority of maintenance and repairs on block or concrete walls can be done by masonry or concrete wall contractors. In extreme circumstance geotechnical engineer may need to be consulted.