You notice it first as a rust-colored streak on a concrete wall, or a chunk of concrete that’s popped off a step, a column, or the edge of a foundation. Underneath, there’s usually a piece of steel that’s been rusting. This is called spalling, and near the coast it deserves its own page.
Why the coast is harder on concrete
Caltrans’s corrosion guidelines treat structures within about 1,000 feet of marine water as exposed to a marine atmosphere, meaning salt-laden air and fog. That’s a highway-engineering threshold, not a map of which houses will spall, but it’s a useful rule of thumb. Much of Leucadia, Old Encinitas, and Cardiff west of I-5 near the beach is inside that kind of distance.
Here’s the mechanism, simply put. Concrete protects the steel inside it by staying alkaline. Over years, chlorides from salt air work their way in, especially through cracks or where the concrete cover over the steel is thin. Once enough chloride reaches the rebar, it starts to rust. Rust takes up more space than steel, so it pushes outward and cracks the concrete from the inside. Pieces break off, more steel is exposed, and the cycle speeds up.
We treat marine exposure as a reason to look, not as a diagnosis. Plenty of old concrete near the beach is fine.
Where it tends to show up
- Foundation edges and stem walls where the concrete cover is thin or the grade is wet.
- Exterior stairs, landings, and balconies, especially ones with steel railings set into the concrete.
- Retaining and garden walls with rebar near the surface. See retaining wall repair.
- Garage slabs and driveways near the beach.
- Steel in crawl spaces: anchor bolts, hold-downs, and connectors. See raised foundation repair.
- Posts and columns with steel bases.
For condo buildings, balconies and other elevated elements have their own inspection law (Civil Code §5551 for HOAs with three or more units). That’s a different scope from foundation repair, but if you’re on a board, it’s worth knowing the two overlap near the coast.
How we assess it
- Sounding. Tapping the concrete with a hammer to find hollow areas that have delaminated but not yet fallen off.
- Crack and stain mapping. Rust stains and cracks that follow the line of the rebar.
- Exposure and cover. How close the steel is to the surface, and how wet the area stays.
- Structural role. Spalling on a decorative garden wall is a maintenance item. Spalling on a footing, a beam, or a balcony support is structural.
When the element carries load, we coordinate with licensed engineers as needed on the repair design.
How spalled concrete gets fixed
- Patch repair. Remove loose concrete, clean or replace corroded steel, apply a bonding agent, and patch with a repair mortar suited to the exposure.
- Section replacement where the concrete is too far gone to patch.
- Coatings and sealers to slow future chloride entry on repaired and nearby surfaces.
- Drainage fixes so water doesn’t sit on or against the concrete. See foundation drainage.
- Replacing corroded connectors in crawl spaces with hardware rated for the exposure.
One honest note: patching over a spall without dealing with the corroded steel is a short-term fix. The rust keeps going and the patch pops off. We’d rather do it right once.
Questions we hear around town
Is a rust stain on my foundation serious?
It means steel near the surface is corroding. Whether it’s serious depends on what that concrete does. Worth an inspection. See foundation inspection.
Can I paint over it?
Paint hides it for a while. The corrosion keeps working behind it.
We live a mile inland. Do we need to worry?
Salt exposure generally drops off with distance from the water, but cracks and wet spots can still let water reach steel.
Is spalling covered by crack repair?
It’s related, but spalling repair also has to address the steel. See foundation crack repair.
Get a Free Quote
Send a photo of the spalling and tell us how far you are from the water. We’ll look at the steel, not just the surface, and give you a Free Quote. See cost factors.