​The Owner’s representative for a heritage brick masonry building wanted to repair the cracks highlighted within the photograph on the left - without a prior condition assessment. Retained as the consultant for the project, I observed that the cracks resembled those caused by differential movement within the natural stone masonry foundations. I also observed that previous attempts at repointing cracked mortared joints had failed.
A review of the damp and deteriorated conditions within the basement confirmed to me that the below grade walls could not have been waterproofed. There was also evidence of debris that could only have originated from the inner core rubble of the traditional mass masonry foundation walls. I therefore concluded that the cause of the problem was the destabilization of the foundations due to water leaching the lime binder from the mortar/grout that had been used during their construction. (Illustrated by the Figure) I also concluded that it would be unwise to repair the cracked brick masonry - without first addressing the problem that caused the cracks. (I also did not charge for the ad hoc condition assessment!)

​Stainless steel helical masonry ties were installed from within the basement to provide the required restraint during grouting, to stabilize the walls during excavation work, and to provide a better composite action across the masonry assembly. The foundation walls were then exposed and waterproofed. The voids within the inner core rubble were then grouted using very low-pressure techniques to inject a lightweight cellular foamed cement grout. Finally the excavations were backfilled and cracked masonry joints were cut out and repointed using a hydraulic lime heritage repointing mortar.

​This project is  one of several case studies discussed within a chapter devoted to “Addressing the Cause - As Well as the Result” within
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MASONRY PROBLEMS
Investigation, Identification & Restoration
Canadian Project Case Studies

The full technical reason for this phenomenon - often referred to as the ring or halo effect - is too involved to explain briefly within this blog. However, I’ve always found the Figure I have included below as very helpful in understanding what can happen.
Often the approach to restoration is to simply remove visibly deteriorated concrete while ignoring the fact that corrosion will continue within the surrounding concrete. However, the repaired areas will change from anodic to cathodic sites, thereby increasing the remaining cathode to anode ratio - this will increase the rate of corrosion of the remaining anodic sites. (as illustrated by the Figure) For this reason, I believe that the use of corrosion evaluation testing methods in conjunction with a delamination survey can be essential.

This and other restoration issue are included in
INVESTIGATING CONCRETE PROBLEMS
Learning from Those Who Learned the Hard Way!