CRACK REPAIR - THE PROBLEM

Masonry crack repair utilises bed joint reinforcement to enhance the tensile, flexural and shear capacity of cracked masonry walls. Cracks in walls are the direct result of movement beyond that which can be accommodated by the construction materials. Typically the wall cracks where masonry is over-stressed and least restrained, such as at window and door openings or at corners. The movement that results in a fractured wall is usually caused by variations in the moisture content of the masonry, or in the ground that supports it, temperature variations or by chemical reactions. Some movements are cyclic and reversible, many are permanent.

Cracks in masonry walls can be divided into three categories:
• active (those which are increasing in width and/or length)
• passive (those which are no longer increasing in width or length) and
• cyclic (those which open and close seasonally).

Unless you know the history of the building, and know that the wall cracks fall into the passive or cyclic categories, determining the type and cause of cracking can be difficult and will require the input of a structural engineer who may need to monitor the cracked brickwork over an extended period of time.

CRACK REPAIR SOLUTION

Generally, cracks that are passive or cyclic and less than 5mm in width can be repaired by simple crack stitching repair techniques that improve the tensile and flexural strength of the masonry such as to accommodate small and/or cyclic movements.

Bed joint reinforcement rods are bonded into mortar joints, at regular intervals, usually 300mm to 450mm apart, to tie the masonry on each side of the crack.

Mortar joints are simply raked out to form slots that extend 500mm either side of the wall cracks. Each slot is thoroughly wetted prior to the application of a proprietary cementitious bonding agent. A masonry repair rod is pushed into the bonding agent such as to fully embed the rod and implement crack stitch repairs without costly rebuilding work and with minimum inconvenience to the occupants.

This effective masonry repair system fully restores the integrity of cracked walls to their pre-cracked state and allows the masonry to behave as a reinforced non-fractured unit.

CRACK STITCHING PRODUCTS

Roll profiled and twisted stainless steel helical reinforcement bars have a nominal ultimate tensile strength that is twice that of rebar, four times that of epoxy glass-fibre rods and seven times that of flat twisted plate [ref: BRE GBG 62].

Having a helical configuration the high tensile rods physically interlock with the bonding agent, exhibiting a unique and resilient torsional spring-like quality that allows small amounts of cyclic movement and recovery to occur without brittle failures.

The angular faces of the helix redistribute tensile forces over the reinforced area to stabilise the structure, making the walls tougher, stronger in flexure and tension and less likely to crack.

Cementitious grouts are the preferred bonding agents for retrospective masonry reinforcement. The use of resins for structural repairs by brick stitching is discouraged unless the load potential on the rod is wholly axial (parallel to the helical rod). When used as a full length rod-bonding agent, for repairing cracks in walls, resins do not cope well with shear forces (perpendicular to the rod) and their use for masonry crack repairs should be avoided where there is cross-plane movement potential