Controlling Cracks: How To Repair Masonry Walls
Cracks in masonry walls are a common structural defect and, upon being noticed, should be immediately remedied to avoid the problem worsening. So, how do they develop and how do i get rid of them?
The masonry materials of your property can only tolerate a slight amount of movement and there are many factors that can cause this movement. Variations in moisture content of the ground and the masonry itself, fluctuations in temperature and chemical reaction are common causes though vibration from living near to busy roads or railways can cause the issue.
The cracks are most likely to develop in corners or at window or door openings because it is at these points that the masonry is most stressed and least restrained. Some of the movements that cause the cracks are permanent but some are cyclic and can be reversed.
This is notoriously difficult for the untrained and can only really be achieved by observing and monitoring the cracks over a period of time to determine if they are active (increasing in size), passive (not increasing in size) or cyclic (opening and closing seasonally). Of course, you don’t want to spend all this time observing as the problem will be getting worse all the time! It’s best to call in the experts who can do a proper survey.
How do I repair the cracks?
Passive and cyclic cracks of less than 5mm in width can be easily repaired with simple brick stitching, a technique that will improve the masonry flexural and tensile strength, allowing it to tolerate these small movements. Active cracks that have exceeded 5mm in length need looking at by a structural engineer. Used alone, a masonry crack stitch system of repair is not reliable enough to solve active crack problems and will require further specifications.
Brick stitching involves bonding shaped, twisted stainless steel rods into walls at regular intervals, much like the stitching done with a needle and thread in fabric. Once installed, the rods cause the cracked wall to behave as an integral, reinforced and non-fractured unit. Stitching rods have a helical configuration which physically interlocks with bonding agent; this gives them a strongly resilient torsional quality, causing them to act like a spring and allow wall movements without cracking and other brittle failure.
It’s a simple and straightforward process. After cutting a horizontal channel into the masonry, preferably at the bed joint to allow for easier disguising of the repair later on, the slots are flushed with clean water to remove loose material and reduce the porosity if the brickwork, then filled with WHO 60 cementitious grout. Don’t forget to leave room for repointing and matching.
The high-performance, shrink-compensated bonding agent is then ready to have the stitching bars encapsulated within, leaving 500mm on either side of the crack dispersing loads evenly throughout the structure of the wall. Make good to disguise the slot and the job’s done.
Can I use resin to bond helical bars?
This would generally be discouraged as resin does not bear shear forces very well when perpendicular to the rod so unless the load potential on the helical bars was totally axial (parallel to the helical rods) then it’s not a good idea. Any potential for cross-plane movement requires high quality cementitious grout.