Ramsay Hall is a 6-storey student residential block at the University College London (UCL) constructed with a concrete frame, concrete floor slabs and brickwork. There are brick slips at all floor levels. The two main elevations are in Whitfield Street and also facing the college internal courtyard.
An inspection of the slab edges identified that the brick slips were inadequately bonded to the structural slab, which itself had failed in places due to corrosion of the reinforcement. In many instances the brick overhang above the slab edges was greater than current standards permit.
We were invited to tender for the remedial works because of our experience in concrete repairs, colour matching mortars and masonry repair and were subsequently awarded the package as a subcontractor to DW Bevan Ltd.
All brick slips were removed from the slab edges to allow inspection of the concrete beneath and overhang of the brickwork above followed by instructions from the client’s structural engineer.
Helifix Helibeams were installed above in areas of excessive brick overhang to strengthen the masonry and allow the slab edges to be repaired in a hit and miss sequence.
Individual bricks above the slab edges were drilled and fixed to the structural concrete using the Helifix DryFix system. Similarly the outer skin of brickwork was retro fixed to the inner skin to all elevations.
Slab edge repairs were carried out using a prebagged polymer-modified mortar. These were either finished recessed to accommodate a coloured mortar that simulated the brickwork or flush over windows to accept a white coating.
Extensive trials were required to produce the mortar that would both match the existing brickwork in both colour and texture.
Other works carried out included concrete repairs to window surrounds and balconies and replacement sealant to expansion joints.
As part of the refurbishment to meet the decent home standards, two residential blocks in Camden Town, London, NW1 were both in need of external concrete repairs, but in each instance was the consequence of very different problems.
The walkways at Cobden House are of filler joist construction, with clinker concrete infills, rendered and painted. Here corrosion was due to water ingress from above and causing spalling on the soffit surface.
Gloucester Avenue is a tiled concrete frame building. Water ingress behind the tiles had caused the reinforcement within the concrete to corrode resulting in concrete spalling and debonding of tiles creating a hazard for pedestrians below.
At Cobden House loose and defective concrete and render were removed. The steel filler joists were then mechanically wire brushed and primed, followed by the installation of stainless steel mesh. High build polymer modified hand placed repair mortars were used for reinstatement. A thin cementitious filler was then applied to the soffits to cover the mapping effect caused by the removal of defective paint, followed by the application of a pigmented anti-carbonation protective coating.
At Gloucester Avenue traditional concrete patch and girth repairs were carried out where localised spalling had occurred. The tiles were reset with stainless steel pins drilled and resin fixed through their faces with a colour match mortar to disguise the pin head.
There was also a concern about the risk of further spalling where there were no signs of deterioration. The application of a migrating corrosion inhibitor (MCI) to the concrete to reduce this risk would have required the complete removal of the tiles. We were able to offer an alternative to this that saved the client both costs and programme.
Holes were drilled through the face of the tile at 200mm centres along the front elevation of the building and Margel Vapour Phase Release pellets were inserted. These act similarly to an MCI without the need to remove any finishes. Tiles were then repaired similarly to where the steel pins were installed.
Banbury Town Hall, built in 1854, is a fine Victorian Gothic building, however due to some poor construction details and a spreading roof, the stone arch between the main hall and high level-viewing gallery had failed some years ago. To prevent further masonry collapse the arch was bricked up.
Once the walls had been repaired and the problems with the spreading roof had been resolved, the local authority decided that the viewing gallery should be reopened and the building returned to its original state. The stonework to the arch therefore had to be strengthened and tied back to the main walls before the infill brickwork could be removed.
From the wide range of remedial ties manufactured by Helifix, CemTies were selected by the historic building consultant at GBS Architects of Oxford as the most appropriate solution. The CemTie is specifically designed for stabilising solid masonry, repairing and securing parapets, cornices and decorative fascias, is ideal for situations and causes limited disturbance.
16mm dia. holes were drilled through the stonework. Helibond grout and the stainless steel tie were then injected into each hole using a pinning nozzle and grout gun.
This method allowed the historic fabric to be retained and the works fully concealed prior to the removal of the infill panel and final decoration.
Masonry problems require the cause to be diagnosed correctly. Only then can an appropriate remedial system be designed and carried out successfully. Remedial works may include:
Structural Renovations Ltd are an Approved Helifix Installer and can offer advice on repair options. In conjunction with Helifix we can provide a full design that can be underwritten by Helifix PI Insurance with 10-year warranties on offer on completed works.