Spalling Concrete in Parking Garages: Causes and Repair

In short: concrete spalls when the rebar inside it rusts. Rust takes up more room than steel, so it pushes the concrete apart from the inside until pieces break off. In parking garages the cause is almost always water and road salt. The repair removes the damaged concrete, treats the steel and rebuilds the section.

What is spalling concrete?

Spalling is when the surface of the concrete breaks off in flakes or chunks. It shows up on slab edges, column corners, ramps, ceilings and walls. Before it spalls, the concrete often delaminates: a layer separates from the concrete behind it, but hasn’t fallen yet. That hidden layer is why engineers sound the concrete before they mark out a repair.

Why parking garage concrete spalls

• Road salt. Cars bring in salty water every winter. Over the years the chlorides soak into the concrete and reach the rebar.
• Freeze-thaw. Water in the concrete freezes and expands, again and again.
• Cracks and leaks. A crack or a leaking joint lets water straight to the steel.
• Thin cover. Where the rebar sits close to the surface, the damage starts sooner.

Signs to look for

• Rust stains running from cracks or from the underside of a slab
• Flaking or popped concrete at column bases, curbs and slab edges
• Exposed or rusted rebar
• Concrete that sounds hollow when tapped
• Water dripping through the slab above, especially after a thaw

How spalled concrete is repaired

1. The engineer surveys the garage and marks the repair areas.
2. The edges are saw-cut and the damaged concrete is removed back to sound material.
3. The rusted rebar is cleaned and treated. Steel that has lost too much is replaced, as the engineer calls for.
4. The section is formed where needed and rebuilt with new concrete or repair mortar.
5. The engineer reviews the repair before the area reopens.

Shoring goes in first where a column, beam or slab has to carry load during the work.

Spalling repair in Toronto and the GTA

We repair spalled columns, slabs, ramps and walls in parking garages and in commercial and industrial buildings, as part of our concrete repair and parking garage restoration work. We work to the restoration engineer’s spec, with our own crews and forms.

Questions people ask

Is spalling concrete dangerous?

It can be. Loose pieces can fall from ceilings and columns, and the rust behind them weakens the steel. Have an engineer look at it early.

Can spalling be patched?

Not well on its own. A patch over rusting rebar usually comes loose again. The damaged concrete has to be removed and the steel treated first.

Who should we call first?

A restoration engineer, who assesses the garage and writes the repair spec. Then a contractor prices and does the work.

Have a repair spec or a garage that needs work?

Send it and we’ll reply the same day. Get a free quote or call (416) 785-7838.