Patio Sinking on One Side: Causes and Repair Options

A level patio doesn't stay that way forever. If one side of your concrete patio has dropped an inch or two — or more — the slab is telling you something is wrong underneath it. Ignoring it leads to cracking, tripping hazards, water pooling against your foundation, and a repair bill that only grows.

This guide covers why patios sink unevenly, how to diagnose what's happening under your slab, and what your actual repair options cost.

Why Does a Patio Sink on Just One Side?

If the whole patio dropped uniformly, that would be one thing. But one-sided sinking tells you the problem is localized. Here are the most common causes:

Soil Erosion and Washout

Water is the number one culprit. When drainage isn't right — gutters discharging near the patio, no grading away from the slab, or just years of rain — water gets under the concrete and washes soil out. This creates voids. Once the void gets large enough, the slab drops into it.

This usually happens on one side because that's where water collects and enters. A downspout on one corner of the house, a low spot in the yard that sends runoff toward the patio — these cause asymmetric erosion.

Poor Soil Compaction at Installation

Concrete patios need a properly compacted gravel base. If the contractor skipped compaction or used the wrong fill material, soil settles over time. It won't settle evenly — areas with looser fill drop faster. This often shows up in the first 3–7 years after installation.

Tree Roots

Roots grow toward moisture. If there's a tree near your patio, roots can grow under the slab, lift one side, then die and leave a void when they decompose. The result: the side that was pushed up is now unsupported and drops. You'll sometimes see cracks running across the slab where the root was.

Plumbing or Utility Lines

A slow leak in a buried water line, irrigation pipe, or even a sewer line under or adjacent to the patio can saturate and erode soil on one side. You may not see or hear the leak — just the sinking.

Clay Soil Expansion and Contraction

In DFW and parts of North Carolina, expansive clay soil is a real issue. Clay swells when wet and shrinks when dry. A patio installed on clay without proper base prep will move with the seasons. If drainage pushes more moisture to one side, that side moves more — and eventually settles lower than the other.

How to Diagnose the Problem Before You Repair

Don't just call a contractor and ask them to lift the slab without knowing what caused the sinking. If you fix the slab without fixing the cause, it'll sink again.

• Check drainage first. Where does water go when it rains? If it flows toward the sinking side of the patio, that's your primary problem.
• Look for voids. Knock on the slab with your fist or a rubber mallet. A hollow sound means there's air underneath — classic void from erosion.
• Check for cracks. Are cracks running across the slab? Is there a pattern that suggests roots or a point-source void?
• Inspect gutters and downspouts. A downspout dumping next to the patio is a very common cause that's easy to fix.
• Look for nearby trees. Any tree within 10–15 feet is a root suspect.

If you suspect a plumbing leak, a plumber can run a camera through the line and pressure-test it before you spend money lifting the slab.

Repair Options: What They Cost and When to Use Them

Option 1: Mudjacking (Slab Jacking)

Mudjacking is the traditional method. A contractor drills 1.5–2 inch holes through the slab, then pumps a slurry mixture of water, soil, and cement underneath. The slurry fills the void and hydraulically lifts the slab back to level.

• Cost: $3–$8 per square foot, typically $500–$1,500 for an average patio
• Timeline: One day. Usable within 24 hours.
• Best for: Slabs with voids from erosion, minor settlement, no major cracking
• Limitations: The fill material is heavy, which can contribute to future settling. Not ideal for slabs in poor condition.

Option 2: Polyurethane Foam Lifting (PolyLifting)

This is the modern version of mudjacking. Instead of a slurry, contractors inject expanding polyurethane foam through smaller holes (5/8 inch). The foam expands, fills the void, and lifts the slab. It cures in 15–30 minutes.

• Cost: $5–$12 per square foot, typically $800–$2,500 for a patio
• Timeline: Half day. Usable within an hour.
• Best for: Slabs with clean voids, areas near plumbing or utilities (lighter material), faster turnaround
• Limitations: More expensive than mudjacking. Not appropriate if the slab itself is cracked and structurally compromised.

Option 3: Grout Injection / Deep Soil Stabilization

For patios sinking due to clay soil or deeper soil instability, grout injection stabilizes the soil underneath the base material — not just the void directly under the slab. This is less common for residential patios but relevant in DFW where clay movement is significant.

• Cost: $8–$20 per square foot depending on depth and scope
• Best for: Patios on expansive clay with recurring settlement issues

Option 4: Remove and Replace

If the slab is extensively cracked, the concrete has spalled, or the sinking is severe enough that lifting won't restore a clean level surface, replacement is the right call. Trying to lift a compromised slab often just reveals more problems.

• Cost: $8–$15 per square foot for a new concrete patio with proper base prep
• Timeline: 2–4 days for demo, base work, pour, and cure
• Best for: Slabs older than 20–25 years, major cracking, multiple repairs already attempted, root damage that fractured the concrete

If you go the replacement route, this is your opportunity to fix whatever caused the original sinking — better drainage, proper compaction, thicker base material, and control joints that give the new slab room to move.

What If There's Only a Small Drop?

If the sinking is less than an inch and the slab is otherwise in good shape, some homeowners choose to grind down the high side rather than lift the low side. This is called concrete grinding or trip hazard removal and costs $3–$6 per linear foot. It won't fix the underlying void but can eliminate the immediate safety hazard while you address drainage.

This is a band-aid, not a fix — but it buys time and removes the trip hazard cheaply.

Address the Root Cause or It Sinks Again

Here's what contractors see constantly: a homeowner pays to mudjack or lift a patio, and 2–3 years later it sinks again because the drainage issue was never fixed. Don't spend $1,000 lifting a slab if a $300 downspout extension or re-grading job would have prevented the problem.

Before any repair, address:

• Gutters and downspouts: Extend them at least 6 feet from the patio. Direct water away from the slab.
• Grading: The yard should slope away from the patio at a minimum 2% grade (about 1/4 inch per foot).
• Tree removal or root barriers: If a root is the cause, removing the tree (or installing a root barrier) is part of the long-term fix.
• Plumbing repairs: If a leak is contributing, fix it before lifting the slab.

A good concrete contractor will assess the cause before recommending a repair method. If they jump straight to mudjacking without looking at drainage, get a second opinion.

Typical Cost Summary

• Mudjacking: $500–$1,500 for most patios
• Polyurethane foam lifting: $800–$2,500
• Slab replacement (200 sq ft patio): $1,600–$3,000
• Drainage corrections (downspout + re-grade): $200–$800
• Concrete grinding (trip hazard only): $150–$400

The most cost-effective path for most homeowners with a structurally sound slab that has settled 1–3 inches: fix drainage first, then mudjack or foam lift. Total investment typically runs $700–$2,000 and buys you 10+ years of stability if the drainage issue is resolved.

Ready to get started? Get a free concrete estimate from a local contractor.