Why Your Concrete is Cracking: 6 Common Causes (And How to Fix Each)

When you notice cracks forming in your driveway, patio, or walkway, the instinct is to worry. In Murrieta, concrete cracking is common — but not all cracks mean the same thing, and not all cracks require the same fix. Here’s how to read what your concrete is telling you.

Cause 1: Shrinkage Cracks During Curing

What they look like: Hairline cracks that form in a random map-like pattern, usually appearing within the first few weeks after a new pour. Often called “crazing.”

Why it happens: As concrete sets, it loses moisture and shrinks slightly. If the concrete cures too fast — common in Murrieta’s dry summer heat — the surface shrinks faster than the interior, creating tension that produces surface cracks.

What to do: Hairline shrinkage cracks are typically cosmetic and don’t affect structural integrity. If the cracks are truly hairline (less than 1/16 inch wide), sealing the surface is usually sufficient. Wider shrinkage cracks may warrant a surface repair.

Cause 2: Missing or Improper Expansion Joints

What they look like: Cracks that run straight across a slab, often at intervals. They may widen or close with temperature changes.

Why it happens: Concrete expands and contracts with temperature. Expansion joints — the deliberate cuts made in slabs — give the concrete room to move without cracking. When joints are missing, spaced too far apart, or cut too shallow, the concrete cracks at the weakest point instead.

What to do: Structural cracks from joint failure can be repaired with epoxy injection or polymer-modified filler. The joint spacing issue can’t be fully corrected without replacement, but sealing the new crack prevents water infiltration that would worsen it.

Cause 3: Tree Root Intrusion

What they look like: Raised or heaved sections with cracks at the edge, often lifting one side of a slab higher than the other. Usually progressive — gets worse year over year.

Why it happens: Established trees — particularly eucalyptus, ficus, sycamore, and Chinese pistache — have aggressive surface roots that grow beneath concrete and lift it as they expand. This is one of the most common causes of driveway and patio damage in Murrieta.

What to do: Repairing concrete without addressing the root problem is temporary. The roots will continue to grow and re-crack any new concrete within 5–10 years. The right sequence is: consult with a certified arborist in Murrieta to assess root removal options, then repair or replace the affected concrete once the root source is resolved.

Cause 4: Clay Soil Shrinkage and Settlement

What they look like: Settled sections — slabs that have sunken below their original elevation, often with cracks at the edges where settling occurred. Common in Menifee, Perris, and parts of Murrieta and Lake Elsinore.

Why it happens: Inland Southern California has significant expansive clay soil deposits. Clay absorbs water and swells; as it dries out in summer, it contracts and creates voids beneath concrete slabs. Over multiple wet-dry cycles, slabs sink into those voids.

What to do: If the slab is structurally sound, mudjacking can lift it back to grade by pumping a grout mixture beneath it. If the slab has cracked significantly through the settlement, replacement may be more practical. Addressing drainage to reduce the wet-dry cycle in the soil helps prevent recurrence.

Cause 5: Overloading or Impact Damage

What they look like: Spider-web or star-shaped crack patterns radiating from a central point. May appear where heavy equipment parked, or where a vehicle dropped a load.

Why it happens: Standard residential concrete is designed for passenger vehicle loads. Heavy trucks, RVs, or equipment can exceed the load capacity of a residential slab — especially if the slab was poured thin (under 4 inches) or with inadequate subbase compaction.

What to do: Impact cracks are typically localized. We can cut out the damaged panel, re-prep the subbase, and pour a replacement section. For areas that will regularly see heavy loads, we recommend a 6-inch slab thickness with heavier rebar spacing.

Cause 6: Water Under the Slab (Erosion or Plumbing Leaks)

What they look like: Soft spots, settled sections, or cracks that develop relatively quickly. Sometimes you can hear a hollow sound when tapping the slab. May appear near irrigation heads or where water pools.

Why it happens: Water washing soil out from beneath a slab — from irrigation runoff, a slow plumbing leak, or poor drainage — creates voids that the slab eventually drops into. This is distinct from clay shrinkage: it’s active erosion rather than seasonal movement.

What to do: Fix the water source first. Then, depending on the extent of voiding, mudjacking can fill the voids and re-level the slab, or the section may need replacement if the void is too large or the slab too damaged.

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When to Call a Professional

If you’re unsure what type of cracking you have, or if cracks are wider than 1/4 inch, have vertical displacement (one side higher than the other), or are progressing in length over time, those are signs to have a contractor assess in person. A quick visual inspection can usually identify the cause and determine whether repair or replacement makes more sense.

We offer free on-site estimates throughout Murrieta, Temecula, Menifee, Wildomar, and Hemet. Contact us and we’ll tell you exactly what you’re dealing with before you commit to any work.