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Structural integrity restored to HA properties

Client: Affinity Sutton Homes
Location: Plymouth, Devon
Approved Installer: RM Construction
Reference No: CS164

This terrace of 22, two storey, housing association properties of traditional cavity wall construction was built in a shallow crescent shape. Prior to an upgrade programme of external wall insulation, a structural survey was carried out which identified masonry cracking of varying degrees. Most of the cracks were on the external rear elevation, although there was also some damage on the front elevation and internally, primarily in homes at the centre of the crescent. Thermal movement, and a lack of adequate movement joints, was the main cause of the problems. The concave shape of the terrace's rear elevation had 'squeezed' the masonry, resulting in deformation of the wall profile, reduction in cavity width and wall tie damage. Structural integrity needed to be reliably restored with the minimum of disruption as the properties would remain occupied during the works.

The Helifix solution

An appropriate repair scheme was devised using a combination of Helifix masonry repair products.

  • To reconnect the external masonry to the main structure at first floor level and restore lateral restraint, eight HD BowTies were installed in the rear elevation of each property. Inserted through clearance holes in the wall, they were power-driven through parallel floor joists before being bonded into the masonry.
  • Some 4,000 DryFix remedial wall ties, of varying lengths due to varying cavity widths, were installed across all elevations and party wall apexes. These were simply power-driven into both leaves, via small pilot holes, for a solid mechanical connection.
  • Remedial movement joints were created between all the properties on both the front and rear elevations. Moveable HeliBars in plastic sleeves were bonded across the vertically cut joint which was filled with a flexible mastic.
  • Cracks were stitched at various locations by bonding stainless steel HeliBars, into channelled-out mortar beds, with HeliBond grout.
  • The rear elevation of one central property was so badly distorted that the outer leaf had to be rebuilt by RM Construction, using StarTies, to reinstate the cavity.

Once all the concealed repairs were completed, with minimal disturbance to the building fabric or the occupants, the properties were structurally secured but visually unaltered. Download the case study