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Crack stitching restores integrity to Northolt flats

Client: Private homeowners
Location: Northolt, London Borough of Ealing
Approved Installer: Structural Renovations Ltd
Reference No: CS132

Built in the 1970's with brick / block cavity wall construction, two separate three storey blocks of six privately owned flats per floor were suffering from widespread subsidence caused by tree roots and desiccated clay soils. This had caused significant internal and external cracking of a stepped, tapering nature affecting both blocks on all storeys and elevations, predominantly around window openings. Two flats were so badly damaged they were no longer habitable and the occupants of all 12 ground floor flats had to be moved out while repair works were undertaken.

The Helifix Solution

Helifix carried out structural repair work to all cracked external walls. In addition, other contractors undertook some localised rebuilding together with major underpinning, which involved removal of ground floor slabs, underpinning external and internal walls with augured piles and casting new cantilevered reinforced concrete beams and slabs.

  • To stitch the stepped cracks, generally around 1-4mm wide, above and below various windows, stainless steel HeliBars were bonded into channelled out mortar beds across the crack using HeliBond cementitious grout.
  • The HeliBars varied in length between 1m, 1.5m and 2m depending on whether they were stitching single or multiple cracks. In all some 60 HeliBars were installed and warranty issued for the structural repairs.
  • Some fully grouted stainless steel CemTies were also installed in areas such as stairwells and bin stores where cracks were located at the building corners.

The Helifix repairs, in conjunction with the underpinning, stabilised the properties, secured the masonry and restored structural integrity. Click here to download the case study.