Problems
Uneven concrete
The concrete no longer sits flat, flush or level with what is next to it.
Uneven concrete comes in two varieties that look similar and need different answers. Either it started level and moved, or it was never level to begin with. On a walk that distinction is visible panel against panel, which is what makes settled sidewalk panels easier to read than most flatwork.
The first is a settlement problem and lifting is relevant. The second is a construction problem, and lifting will not help — you cannot raise concrete to somewhere it has never been. Where the difference is small and confined to one joint, grinding and lifting are the two realistic answers, and which one applies depends on that same distinction.
Telling the two apart
Settlement usually leaves evidence: a step at a joint where two panels have parted company, a gap where the slab has pulled away from a step or wall, cracks that have opened along the low side, or a slab that has tilted rather than dropped evenly.
An original pour problem tends to be smooth and continuous. There is no step, no gap, no cracking pattern that follows the low area — the surface simply runs the wrong way. Water pooling in the middle of an otherwise undamaged patio, with no sign of movement anywhere, often points this way.
What each one needs
Settlement can often be corrected by lifting the slab back to height, provided the concrete is sound. That is the straightforward case.
A pour that was never right is harder. Options narrow to replacing the affected area, or building the surface up with an overlay or self-levelling material where the depth involved is small and the setting is interior or protected. Neither is a cheap correction to a cheap mistake.
Where unevenness matters most
At doorways and thresholds, where a change in height affects how a door swings and where water goes. At the top and bottom of steps, where uneven risers are a genuine fall risk. Anywhere water now runs toward the house rather than away from it.
On an open patio, a quarter of an inch of unevenness is cosmetic. At the top of a flight of steps it is not.
Measuring it before you call anyone
Ten minutes with a straight edge turns a vague complaint into something a contractor can quote against. Lay a long level or a straight board across the affected area and measure the gap under it at the worst point. Do the same across the joint where two sections meet, and note which side is high.
Photograph the level in place with the measurement visible. It sounds fussy, and it is the single most useful thing you can hand somebody who has not seen the property, particularly if you are collecting more than one opinion and want them working from the same facts.
Also check whether the surface runs away from the building or back toward it. A bucket of water poured at the high point will show you in seconds, and which way it goes changes the priority more than the size of the difference does.
What to ask a contractor
- Do you think this settled, or was it poured this way?
- What evidence are you using to decide that?
- If it settled, is the slab a lifting candidate?
- If it was poured this way, what are the realistic options and what do they each cost?
Before you ask anybody for a price
Four things worth settling first. None of them needs a contractor, and none of them needs your contact details — they are simply what separates a useful conversation about an uneven surface somebody has to walk on from an expensive guess.
Cosmetic, functional or structural
We cannot tell you which of these applies to your property — nobody can from a distance. What follows is how the three differ, so you can look at your own with a clearer question in mind.
- Cosmetic is an unevenness you notice only when looking for it, which nobody catches a foot on and which does not pond water.
- Functional is the lip people actually trip on, or the low spot that holds water long enough to matter. This is where most unevenness sits, and it is a safety question before it is a repair question.
- Structural is where the unevenness is a symptom of something moving underneath rather than of wear on top — a whole section tilting rather than an edge wearing down.
- Direction separates the two most common causes: a section standing proud of its neighbours suggests something pushing up, and a section sitting low suggests support that has gone.
What to record before requesting proposals
Contractors price what they can see. Arriving with these already noted is the difference between quotes you can compare and quotes you cannot.
- The height of the worst lip, measured against a coin or a tape in the photograph rather than described in words.
- Where it sits on a route people actually use, and whether that route is used after dark or by visitors rather than only by the household.
- Whether the raised side is nearer a tree, a bed or a boundary — or nearer the house and the ground that was worked during building.
- Anything already done about it, including temporary measures, because a repair that did not hold is useful information.
Keep it in the Project Brief if you would rather not lose track of it — it prints to something you can hand to whoever comes out.
Signs that justify getting somebody out sooner
These are observations, not deadlines. Nothing here is a reason to rush a decision; they are the situations where waiting has a cost worth knowing about.
- The lip is on a route the public uses, or on a route somebody uses in the dark.
- Somebody has already caught a foot on it, whether or not they were hurt.
- The difference is growing between one season and the next.
- It sits on a shared or public boundary surface where responsibility may not be yours alone.
What not to assume
- That grinding the lip solves the problem. It removes the hazard and leaves whatever created it doing exactly the same thing.
- That a section pushed up by growth can simply be reset. Put it back and the growth resumes; the repair expires by design rather than through poor workmanship.
- That the hazard can wait for the wider decision. Addressing a trip risk and deciding the future of a surface are two decisions on two timescales.
- That because it is outside, it is nobody's liability. Who is answerable depends on where the boundary falls, and that is worth establishing.
How we know what this page says
Each of these is something this page says. What follows is why we say it, what we had to assume, and what would change our mind — so you can weigh it rather than take it on trust. How we grade what we publish.
Concrete that is uneven does not automatically need replacing.
Strong field consensus Most experienced people would say the same thing, though it rests more on accumulated field experience than on anything formally settled. You will find few practitioners who disagree, and some who qualify it.
Evidence considered
- Unevenness is a description of where the slab sits, which can change without the concrete itself deteriorating.
- Several repair categories exist specifically to correct position while leaving sound concrete in place.
- The condition of the concrete and the condition of what supports it can differ independently.
- Where a previous position correction was carried out and did not hold, that is evidence about whether the movement is still active.
Still to establish
- Void depth and extent
- Subgrade and compaction
- Whether damage is surface or full depth — partly, on your own
- What the concrete adjoins — partly, on your own
- Previous repairs — you can check this yourself
Why we say this, and when it may not apply
It is the most common assumption homeowners arrive with, and acting on it is expensive. Unevenness describes position; replacement addresses condition, and the two are separate questions.
What we had to assume
- That the concrete itself is structurally sound rather than broken through its depth.
- That whatever moved the slab can be identified and, where it is still active, addressed.
When this may not apply
- Where the slab has broken into multiple pieces that move independently, position correction has little to hold.
- Where the surface has deteriorated through its depth as well as moved, correcting position leaves the other problem.
- Where the concrete adjoins or supports part of the building, the question stops being a paving question.
What would change it
- Evidence that the slab is cracked through its full depth in more than one place.
- Evidence that the ground is still moving, which would undo a position correction.
- Finding that the slab is tied into a foundation rather than independent of it.
- Finding that a previous correction was already tried here and did not hold.
Strong field consensus does not mean this: It does not mean the question is closed, and it does not mean a contractor who sees it differently is wrong or dishonest. Consensus is a description of what most people think, which is not the same as proof.
A tree near displaced concrete is not by itself evidence that roots caused it.
Mixed evidence Competent, honest people reach different conclusions here, and the disagreement is real rather than a matter of one side being out of date. Both positions have support and both have failure cases.
Evidence considered
- Roots can and do lift concrete where they grow beneath it.
- Trees and slabs on the same property also respond to the same soil and moisture conditions, producing correlation without causation.
- Removing a mature tree can itself cause ground movement as soil moisture changes.
Still to establish
- Trees and roots — partly, on your own
- Soil movement — partly, on your own
- Subgrade and compaction
Why we say this, and when it may not apply
Root damage is real and common enough to be the first thing people reach for, which means it is also the most frequently misattributed cause. Removing the wrong tree is not reversible.
What we had to assume
- That whether roots are actually under the slab can be established, which often requires excavation.
- That the species and its rooting habit are identifiable.
When this may not apply
- Where roots are visibly under and against the slab, the causal path is direct.
- Where displacement follows the line of a visible root, attribution is much stronger.
What would change it
- Excavation at the edge showing whether roots are beneath the slab.
- The species and mature rooting habit of the tree in question.
- Whether displacement follows the root line or the slab geometry.
Mixed evidence does not mean this: It does not mean the choice does not matter, and it does not mean you should pick whichever is cheaper. It means the deciding factor is usually something specific to your property rather than a general rule.
Common questions
Can uneven concrete be ground down instead of lifted?
Grinding can remove a small offset at a joint and is a legitimate answer to a trip hazard where appearance is not a priority. It leaves a visibly different finish, it cannot correct slope, and it does not address why the slab moved. It is a targeted fix for one specific problem rather than a general one.
Is self-levelling compound an option outdoors?
Most self-levelling products are formulated for interior use and do not hold up to freeze–thaw cycling and UV exposure outdoors. Ask specifically what a contractor is proposing and what it is rated for before agreeing to it on an exterior slab.
Work it out, or judge the quote
Related guides
Sunken concrete
A slab that now sits lower than it should — almost always a ground problem, not a concrete problem.
Read more →Trip hazards
A step at a joint in a walkway or drive — the most common reason homeowners finally act.
Read more →Concrete leveling
Raising settled slabs back toward their original height instead of tearing them out.
Read more →Concrete settlement
The process behind sunken slabs: why ground loses volume and what makes it stop.
Read more →Repair or replace?
The central question: when repair holds, when it is money spent twice, and how to tell.
Read more →