Spalling Concrete Repair Ottawa

What spalling concrete means on a foundation

Ottawa Parging Experts treats spalling as a substrate problem rather than a finish problem, because with spalling the wall itself is coming apart and the parge coat is only the casualty sitting on top of it. Where a soft coat turns to powder and a debonded coat lifts in plates, spalling leaves craters. You can see rounded stone aggregate standing proud in the bottom of the void, or the hollow cells of a concrete block, or in the worst cases a rusted bar of reinforcing steel.

Depth is the give-away. Parge coats are usually somewhere between a quarter inch and half an inch thick, so a defect that stops at that depth is a coating failure. Once the void goes deeper and you are looking at stone, sand, and cement paste rather than a smooth grey skin, the concrete is spalling. Poke into the crater with a screwdriver. If material keeps coming out and the hole gets deeper as you go, the damage is still live rather than an old scar.

Exposed steel changes the conversation. Rust occupies several times the volume of the metal it came from, so a corroding bar works as a slow wedge that keeps pushing concrete off from the inside. A spall with a rust stain running down from it is not going to stabilise on its own, and it is worth having looked at rather than left through another couple of winters.

Why concrete spalls on Ottawa foundations

Concrete spalls when water gets into it and then freezes. Ottawa supplies both conditions generously. Industry guides for this market estimate 50 or more freeze-thaw cycles a year, and around 17 nights annually drop to -20°C or colder, nearly all of them in January. Water held in the pore structure expands as it freezes, and if that expansion has nowhere to go it fractures the paste holding the aggregate together. Repeat that a few dozen times a winter across a few decades and the surface layer separates and falls.

Some concrete is more vulnerable than the rest from the day it was placed. Pours made with too much water, poorly consolidated walls with honeycombing behind the forms, and older foundations built before air entrainment was standard all have a more open pore structure for water to occupy. Block walls have a weak point of their own: the face shells are thin, and once water reaches the cores through a cracked joint, freezing pushes those shells off in slabs.

Position tells you the rest. The band from grade to roughly 12 to 18 inches above it takes the worst of the punishment, because that is where snow piles against the wall, where meltwater runs down, and where de-icing salt tracked off driveways and walkways ends up. Chloride pulls moisture in and attacks embedded steel, which is why the deepest craters on an Ottawa house are usually on the driveway side, at the base of steps, or beside a walkway. Much of the region also sits on Leda clay, the sensitive marine clay left behind by the Champlain Sea, and a wall that has moved on that soil has cracks for water to enter through.

Rebuilding spalled concrete before parging returns

Coating over a spall is a cosmetic act with a short shelf life. A parge coat spanning a void has nothing behind it to carry load, the crater underneath keeps holding water, and deterioration continues out of sight until the patch drops off and the hole is bigger than it started. Substrate first is not a preference here, it is the order the physics requires.

The repair begins by removing everything unsound. We chip out to solid concrete all the way around the crater and cut the perimeter square, slightly undercut rather than feathered, so the new material is locked into the wall. Where reinforcing steel is exposed we expose it fully, clean the corrosion off, and treat it, because leaving rust buried under a patch means the wedge keeps working.

The void is then rebuilt with repair mortar in lifts, keyed to the prepared edges and brought back flush with the surrounding wall. Only once the substrate is sound and cured does a new coat go on, and for that we use polymer-modified, fibre-reinforced cement parging, or flexible acrylic parging where the wall stays damp or has a history of movement. We will point out the drainage problems feeding the spall as well, because a rebuilt crater in a wall that is soaked six months a year is a repair on a timer.

What spalling concrete repair costs in Ottawa

Spalling prices on depth and area rather than on the square footage of coating involved, because the labour sits in the removal and the rebuild. A single shallow crater on an otherwise sound wall generally falls in the $300 to $600 patch range. Several spalled areas, or one deep pocket with steel to clean and treat, usually lands between $600 and $1,500. Where spalling runs along a whole wall or the substrate has failed in several places, the rebuild plus a recoat runs $1,500 to $6,000, and a full perimeter recoat prices at $15 to $30 per linear foot, roughly $2,250 to $4,500 on a typical 150 linear foot home.

Repair mortar and parging both need above-freezing temperatures to cure, so the working season here runs spring through fall, about 158 frost-free days from late April to early October. If what you have is a shallow surface pop that has not changed in years, we will say so and leave it alone. If steel is showing, we will tell you that too, and explain why waiting on that one usually costs more than dealing with it.