It often begins with a thin brown line on the underside of a balcony. A year later the line is a crack, and one morning a piece of concrete is lying on the pavement. This is spalling, and it is common on an island where sea air reaches almost every building. It is also one of the home problems that you should not leave until later.
What is actually happening
Reinforced concrete relies on the concrete to protect the steel inside it. Over time, moisture and salts work their way through cracks and porous or thin concrete until they reach the bars. The steel then rusts, and rust takes up more space than the steel it replaces. That expansion pushes outward until the concrete cover cracks and falls away, which exposes more steel to the weather.
Balconies are especially vulnerable. They are exposed on several sides, they often hold water on top, and their thin slabs may have little concrete covering the steel. Coastal homes get more salt, but inland buildings are not immune.
The signs, from early to urgent
- Rust-coloured staining on a soffit, edge or wall
- Hairline cracks running in straight lines, often following the bars
- Bulging or flaking paint that keeps coming back
- A hollow sound when an area is tapped gently
- Pieces breaking away and visible rusty steel
- Sagging, wide cracks or movement in the balcony
If concrete has already fallen
Treat this as a safety issue. Keep people off the balcony and prevent anyone walking beneath it if you can do so safely. Remove anything heavy from the balcony, and get a perit to assess it promptly. If there is an immediate danger to people below, contact the emergency services. Do not stand underneath it and knock pieces loose unless a professional has told you to.
Who to call
Start with a perit if steel is heavily corroded, cracks are wide, the balcony has moved, or you are unsure how serious it is. They can assess the structure and specify the repair. For localised damage that has already been assessed, a mason can carry out the concrete work, and a waterproofing specialist can deal with the water getting in from above.
In an apartment block, sort out responsibility first. Balconies can raise questions about what is private and what is shared, so check your contract and speak to the administrator. Our guide to common-area repairs explains how to approach this conversation.
What a proper repair involves
A repair that lasts usually follows this order, adapted to the perit's or contractor's specification:
- Remove all loose and contaminated concrete, going back to sound material.
- Expose the corroded steel and clean it thoroughly.
- Protect the steel, or add or replace bars where too much has been lost.
- Rebuild the section with a suitable repair mortar.
- Finish and protect the surface with a coating that suits the location.
- Fix the water source, including falls, drains and balcony waterproofing.
The common failure is skipping straight to step five. Filler and paint over active corrosion can look neat for a season, while the steel continues to rust behind it.
Questions to ask before you book
- How will you find the full extent of the damage, not only the visible patch?
- How will the steel be cleaned and protected?
- Which repair product will you use, and why?
- What will you do about water entering from above?
- What access is needed, and who will arrange any permits for works over a street?
Exterior access and street obstruction can affect both cost and timing, as our facade painting guide explains. Post photos of the soffit, top surface and any exposed steel on Qabbad, and ask each provider to quote against the same scope.
Frequently asked questions
Is spalling concrete dangerous?
It can be. The immediate risk is falling pieces, and advanced corrosion can also weaken the structure. Any falling concrete, exposed steel or balcony movement should be assessed promptly by a perit.
Can I just patch and paint a spalled balcony?
Not if the steel is corroding. A surface patch hides the problem while rust continues underneath, so the repair can crack again. The corroded steel and contaminated concrete need to be dealt with first.
Why is spalling so common in Malta?
Salt-laden air, moisture and ageing reinforced concrete are a difficult combination. Water pooling on balconies and limited concrete cover over the steel can speed up the process.