What is Crack Stitching?
Crack Stitching is a term used when remedial works are carried out to stabilise or reconnect brickwork or masonry that has cracked for some reason or other.
Causes Of Cracked Walls
Subsidence is the downward movement of the ground and is not connected to the weight or load of the building and will occur irrespective of whether there is a building there or not.
Settlement is the downward movement of the ground due to the loading of the building/superstructure built upon it. Clay soils can suffer from long term settlement when associated with wet ground conditions.
However, before remedial works are undertaken it is important to understand what causes brickwork/masonry to crack. There are many causes of cracking to brickwork/masonry and we will look at some of them below.
Granular soils ( ie sand and gravel) tend not to suffer from long term settlement as these types of soil generally settle immediately the load of the building is applied.
A typical cracking pattern is diagonal stepped tapering cracking. The crack will tend to be wider at the top and the crack will usually run through weak points such as windows and door openings.
The cracks with this form of movement generally increase in width the higher the cracks rises. Where subsidence is associated with clay soil then the volume of the clay changes with moisture content changes ( ie seasonal changes) and so the crack may open and close dependant on the moisture content of the clay substrate. This movement is called cyclical movement.
Trees and Drains
When tree roots are growing in close proximity to the foundations of a building or wall then the roots can extract water from the substrata and this is a particular problem with clay based soils. Vegetation and tree roots tend not be a problem with more sandy or granular soils.
Drains can become fractured by ground movement or tree root interference and this can have an effect of washing away the “fines” of the soil causing erosion or softening of the clay which will again affect the structural capabilities of the foundations to with stand the loading of the wall/building
This is more common in older properties and may affect all or only part of the structure.
It is usually caused by strip foundations being inadequate to support the imposed loading of the superstructure or when the strip foundations are too shallow and affected by the shrinkable cyclical movement of clay strata or poor ground conditions.
This is the upward movement of the soil and is usually associated with clay soils that have dried and then rehydrate and thus expand in volume. This is often associated where trees have been removed during the construction process and the roots are therefore no longer extracting water from the substrate.
As differing construction materials have varied properties in relation to expansion and contraction with both temperature and moisture content changes then the combined effect of this could be fracture/ bulging of the brickwork.
This is caused when the weight of the roof load “ pushes” against the vertical walls where there is insufficient lateral or roof restraint/tie.
The tops of the walls can be displaced outwards and a crack then occurs between the internal partition walls and the external walls.
The structural failure of lintels due to decay/corrosion or inadequacy can produce diagonal cracks above openings.
Repairing Cracked Brick Walls
It is important to understand why the brickwork or masonry has cracked in each individual circumstance and to ascertain if the movement/defect causing the cracking is historic or ongoing.
If the causation is ongoing then merely “tying” the brickwork together may not be sufficient to overcome any ongoing movement. A structural engineer should be consulted to confirm if the causation is current or historic prior to any remedial measures being undertaken.
How Crack Stitching is Carried Out?
Generally, cracks in brickwork that have been classified as passive or historic or that are due to cyclical movement, can be reinforced by crack stitching methods that will improve both the tensile and flexural strengths of the brickwork panel.
Stainless steel helical reinforcement bars are bonded into the mortar joints with strong grout or resin stretching either side of the crack and at vertical intervals of between 300mm and 450mm. This then ties the brickwork/masonry on either side of the crack.
Mortar joints are raked out using a special grinding tool to 500mm on each side of the crack. The joints are then thoroughly wetted to remove dust and debris and the specialist fixing grout is installed into the raked out joint using an applicator gun.
A stainless steel helical crack repair bar is then pushed into this applied grout to fully embed the bar in the grout. The joint is then repointed to match existing.
This effective system of masonry crack repairs fully restores the integrity of cracked walls to their pre-cracked state and allows the masonry to behave as a reinforced non-fractured unit.
Where the cracks extend around the corner of the building then this system of crack stitching can be extended around the corner of the brickwork thus substantially reinforcing the corner brickwork as well as the brickwork on either side of the crack.
Contact A Wall Crack Repair Specialist
If you have any questions regarding crack stitching then contact one of our wall crack specialists here at Timberwise. We have over 50 years of experience in providing wall crack repair services across England and Wales. Contact our team by calling us on 0800 288 8660 or getting in touch online.