Water damages concrete by soaking into its pores, carrying salts to the surface, rusting the steel inside and, in colder parts of Arizona, freezing and expanding. Over time that shows up as cracks, white residue, flaking and a slab that loses strength. Most Arizona homes sit on a concrete slab, so this matters even if you never think about your foundation.
How does water get into concrete?
Concrete looks solid, but it is full of tiny pores and channels. Water moves through them by capillary action, the same way a paper towel pulls up a spill. It gets in through:
- Cracks in the slab, patio or driveway
- Control joints and cold joints where separate pours meet
- Gaps where pipes pass through the slab
- The slab edge, where soil meets the foundation
Inside the house, the most common source is a plumbing leak under the slab. Copper lines buried in concrete can develop pinhole leaks after years of hard water and heat. Outside, monsoon runoff that pools against the foundation does the same work from the other side.
What water does to concrete over time
| Problem | What happens | What you see |
|---|---|---|
| Efflorescence | Water dissolves salts and leaves them on the surface as it evaporates | White, powdery residue |
| Rebar corrosion | Steel inside rusts and expands, pushing the concrete apart | Rust stains, cracks along a line |
| Spalling | The surface layer breaks away | Flaking, pitting and chips |
| Freeze-thaw damage | Water in the pores freezes, expands and cracks the surface | Scaling on patios and walkways |
Freeze-thaw damage is mostly a high-country problem. In Flagstaff, Show Low or Prescott, a soaked patio that freezes overnight can scale and crack in a single winter. In the low desert, heat and repeated wetting and drying do more of the work.
Signs of water-damaged concrete
- White efflorescence on the slab, garage floor or block walls
- Cracks wider than about 1/8 inch, or cracks that keep growing
- Spalling, where the top layer flakes off
- Dark, damp patches that stay wet even on a hot day
- Warm spots on tile floors, which can point to a hot-water leak under the slab
- Flooring that lifts, cups or loses its bond with the slab
Drying a wet slab
A slab holds water far longer than the air above it. Fans can make the surface look dry while the concrete underneath is still wet, and flooring laid over a wet slab can fail months later. Professionals check the concrete itself with moisture meters and run dehumidifiers for several days. If the water came from a sewer backup or floodwater, the surface also needs cleaning and disinfection.
The EPA advises drying water-damaged areas within 24 to 48 hours to prevent mold. Concrete itself doesn't grow mold easily, but the carpet pad, baseboards and drywall touching it do.
How to protect concrete from water damage
- Point downspouts at least 4 feet away from the foundation.
- Grade the soil so it slopes away from the house.
- Seal cracks under 1/8 inch with a concrete crack filler.
- Fix plumbing leaks quickly, and have a plumber check for a slab leak if your water bill jumps for no reason.
- Dry the slab fully after any leak before new flooring goes down.
If water is already on the floor, start with emergency water extraction. Our structural drying service dries the slab and everything on it. Wide or growing cracks are a job for a structural engineer or foundation contractor, and any mold that follows calls for mold remediation.