Crack Repair and Refurbishment at City Library
The Welwyn Garden City Library in London has recently been fully refurbished, a process in which Twistfix-registered contractors Newman Building Solutions played a key role. During removal of the library's original windows to install modern aluminium frames, carried out by principal contractor's, major cracking and rotation of masonry panels was discovered above all of the openings and window spans. This cracking had compromised the structural integrity of the entire building and posed a significant health and safety risk.
Consultants from the MACE group undertook several structural surveys and designed a comprehensive scheme to restore the council-owned building's lost structural integrity. This involved diagnosing the cause of the severe cracking and rotation suffered by the masonry panels and proposing a repair design to carry out the remedial work.
The results of these surveys showed that the original construction of the building had been defective. When brick panels are built onto a concrete frame, it is normal for up to a third of brickwork to overhang the concrete toe. It was discovered at Welwyn Garden City Library that defective concrete had led to the brickwork hanging more than halfway over the concrete toe and causing the masonry to bow outwards and sag. Some areas of the brickwork had completely collapsed as well as the extensive rotation to the loose brick slips. Even the concrete toe itself had suffered severe concrete failure caused by reinforcing rods oxidising due to the flawed nature of the original build where misplaced reinforcements had allowed water to penetrate.
To prevent further sagging, Twistfix helical bars were installed deep into the brick panels to form masonry beam that spread structural load. Twistfix wall ties were chosen to allow the work to progress rapidly as these fixings become load-bearing upon installation, eliminating the setting-time that prevents the restoration of structural integrity during crack stitching. Crack repair was carried out after the cracks were raked to a depth of 45mm before being injected with high-strength, rapid-setting Twistfix epoxy resin, giving a strong and durable bond between the displaced sections of masonry. The concrete toe was swiftly repaired with the use of a zinc-rich primer to seal it and prevent any further corrosion. A heavy-duty repair mortar was then applied to further strengthen the concrete before brick slips were re-affixed to the toe with cementitious grout
This entire masonry repair scheme was expertly designed and provides a permanent solution, covered by a 20-year insurance-backed guarantee. As IGL members and approved Twistfix contractors, Newman Building Solutions were able to provide this guarantee as standard.
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