The ravages of time are particularly noticeable on high-rise balcony structures, where weather conditions can play havoc on even the most basic elements of a building. Canadian cities are full of once attractive residential towers that are unsightly as well as unsafe due to the structural damage to balcony slabs and railings.
Take, for example, a 30-year-old, eight-storey apartment building in Ottawa that had such badly deteriorating balconies and railings that the tenants could no longer use them.
On top of safety issues, the condition of the balconies and railings made the building unsightly, reducing the building’s curb appeal, and possibly its marketability. Delaying repairs could have led to more severe deterioration and, in time, higher repair costs.
In order to restore the structural integrity of the balcony slabs, the building owner undertook a major rehabilitation project — the first major work on the balconies since the building first opened.
It all began with a pre-construction survey detailing the remedial measures required and an estimate of overall costs.
The scope of the work
The reinforced concrete building had a brick masonry façade. There were 56 reinforced concrete cantilevered balcony slabs, with a total area of 463 square metres. Balcony railings consisted of steel handrails with intermediate metal panels. The balcony slabs and railings exhibited extensive deterioration. The most severe concrete delamination and spalling were along the balcony edges, the result of freeze-thaw action.
On some balconies, crumbling concrete forced the building’s owners to remove concrete fragments and shore the edges of the slab. Exposed reinforcing steel was visible on some balconies, and the metal railings showed significant corrosion on the panels, handrails and the railing posts. There were loose railing anchors and the railings no longer met current Ontario Building Code (OBC) requirements.
Jamie Shipely, senior research consultant of the Canada Mortgage Housing Corporation, says that the owner had no choice in the matter. The slabs had to be repaired or replaced (and upgraded to meet OBC standards), and the new exposed concrete had to be protected from moisture and freeze-thaw damage.
Work was carried out over a seven-month period. Workers removed and replaced deteriorated concrete with Portland cement concrete for through-slab repairs, and polymer-modified concrete and repair mortars for patching repairs. Since more than half of the building’s balconies required major through-slab repairs, it was essential to carefully plan and execute shoring, formwork and concrete placement.
The contractor used a two-component, multi-coat membrane over the new exposed concrete slabs. The polyurethane membrane is waterproof and applied in liquid form. It is designed for heavy use.
The balcony railings were removed and replaced with custom fabricated, galvanized steel railings. Before installation, they were coated with polyurethane enamel.
In the end, all involved considered the project a triumph.
Shipley says that the work restored the structural integrity of the balconies, thereby extending the service life of the balcony slabs.
He adds that the success was in the project’s problem-solving approach, particularly in the detailed survey of balcony conditions before work began. The survey allowed everyone to have a clear idea of the scope of the work needed, something that Shipley says was key.
Paula Gasparro is manager of business development, multi-unit mortgage insurance, at the Canada Mortgage and Housing Corporation.