Causes, Repairs, and Prevention
of Concrete Spalling

Concrete spalling is a common occurance, especially on exterior surfaces that are exposed to freeze and thaw cycles. It's like scaling, but involves bigger chunks breaking loose for no apparant reason.

This kind of spalling is due to corrosion of the steel reinforcement. It can be repaired successfully to extend the life of the structure.	Common spalling on aged exterior concrete. Some prevention and maintenance can significantly delay deterioration.

Common Causes

Low Quality Mix... A cheap/weak concrete mix can result in many problems including spalling.

Improper Installation... Placing and finishing techniques play a huge factor in strength and durability of concrete. Pouring and finishing too wet are big culprits.

Mix Contamination... Sometimes foreign substances get accidentally suspended in the mix. Example: A chunck a mud falls off someone's boot and ends up embedded near the surface.

Corrosion... Corroding rebar overtime will also cause the concrete to deteriorate prematurely and break apart.

Extreme Heat... This is a rare occurance, but concrete exposed to high temperatures, such as a fire, can spall.

Repairing

1. Chip out the edges of the spalled area and use a hose to clean out the hole.

2. Mix up a batch of concrete repair mortar. If the hole is deeper than an inch, add some small gravel to the mix such as pea gravel. Make sure the repair mortar contains a bonding agent or add some liquid bonding agent to the mix.

3. Place the mortar in the hole and smooth with a trowel. Don't overwork it.

4. When it begins to harden brush it lightly with a damp brush for better appearance.

5. For curing, brush some clear sealer over the surface before it gets too hard and begins turning white. If you don't have any sealer, keep it covered with a damp towell for a few days.

Prevention

The most obvious and easiest way to prevent spalling is to use a high quality concrete mix and ensure installation is done adequately. Don't add too much water to the mix and don't finish when bleed water is present, and don't water to the surface to aid in finishing.

Maintain a protective water-repelling sealcoat. Concrete should be resealed every couple of years. This can prevent many issues as well as add years to the life of the concrete.