How we know

How we know what we publish

Everything on this site is hedged, because concrete problems genuinely are. That is not useful on its own — two hedged sentences can be hedged for completely different reasons, and a reader has no way to tell which parts of what they are reading will hold up. So every claim we make carries a state naming what kind of statement it is.

There are 6 of them. They are not a scale, there is no score, and none of them is a percentage. Two of them mean we are not making a claim at all.

The 6 states

Each one says what it asserts and — the part that matters more — what it is not asserting. A confidence label read on its own turns into a guarantee, and the only reliable fix is to put the boundary next to it.

Established practice

This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

What it does not mean

It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

What to do with it

You can reasonably expect a contractor to be familiar with this, and it is fair to ask why if their proposal departs from it.

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.

What it does not mean

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.

What to do with it

Treat a proposal that contradicts this as something to ask about rather than something to reject. A good answer exists more often than you would expect.

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honest people reach different conclusions here, and the disagreement is real rather than a matter of one side being out of date.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.

What it does not mean

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.

What to do with it

Ask each contractor what would have to be true for them to change their recommendation. The answer tells you far more than the recommendation did.

Site dependent

There is no general answer worth giving. The right conclusion turns on conditions at your property — soil, drainage, what is under the slab, what has been done before — and those differ enough that a general rule would be misleading.

What it does not mean

It does not mean nothing can be known, and it is not a way of avoiding the question. It means the information that settles it is at your property rather than in an article.

What to do with it

Gather the specific observations that make the difference. The pages here name them, and having them in hand shortens the conversation considerably.

Inspection required

This cannot be settled without somebody qualified being present. Not because the question is difficult in principle, but because it depends on something that has to be measured, opened up, or seen in person.

What it does not mean

It does not mean the situation is serious, and it does not mean you are being pushed toward paying for an inspection. Plenty of things in this category turn out to be minor once somebody looks.

What to do with it

Nothing you read online closes this one. What you can do is arrive at the inspection with the observations that make it quicker and cheaper.

We make no general statement in this state. Where you see it, we are telling you the answer is not available from a website — not offering a weaker version of one.

Not established

We do not have a basis for a claim here. Either the question has not been settled in any way we can point to, or the honest answer is that we have not established it and are not going to guess.

What it does not mean

It does not mean the answer is unknowable or that nobody knows. It means *we* do not have grounds to tell you, and saying so is more useful than filling the space.

What to do with it

Ask somebody who can actually establish it, and be sceptical of a confident answer from anybody who has not looked.

We make no general statement in this state. Where you see it, we are telling you the answer is not available from a website — not offering a weaker version of one.

What sits behind a claim

Grading a sentence is easy. The work is in writing down what stands behind it, so every claim on this site has a record answering the same five questions: why we say it at all, what we considered, what we had to assume, when it stops applying, and — the one most often left out — what specific thing would change our mind.

A claim with nothing that would change it is not a claim, it is a position. Our own checks reject a record that leaves that field vague, which is why you will not find “more information would be needed” in any of them.

We currently publish 20 of these. Every one is listed below, grouped by state, so you can see the grading across the whole set rather than one page at a time.

Established practice (10)

Lifting methods depend on the slab being sound enough to move as a unit.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Lifting works by raising the slab from beneath, which requires the slab to transmit that force across its area.
A slab already broken into small pieces moves as pieces rather than as a slab.
The method is well established where the precondition holds and is not seriously contested.

Still to establish

Slab thickness — partly, on your own
Crack activity — you can check this yourself
Void depth and extent
Soil movement — partly, on your own

Why we say this, and when it may not apply

It is the practical constraint that decides whether lifting is even on the table, and it explains why one contractor may rule it out where another proposes it.

What we had to assume

That the extent of cracking can be established well enough to judge whether the slab acts as a unit.
That there is material beneath capable of taking the lifting pressure.

When this may not apply

Heavily fragmented slabs, where lifting can widen existing breaks rather than restore level.
Very thin sections, which can crack under the lifting itself.
Situations where the cause of settlement is still active and would resume afterwards.

What would change it

Finding cracking more extensive than the surface suggests, once an edge is examined.
Finding the slab thinner than assumed.
Establishing that the ground is still moving rather than having settled and stopped.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

A crack does not on its own establish that anything has settled.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Concrete shrinks as it cures and cracks in response, independently of what is beneath it.
Restrained movement, thermal cycling and loading each produce cracking without settlement.
Settlement cracking tends to be accompanied by vertical displacement, which shrinkage cracking usually is not.

Still to establish

Crack activity — you can check this yourself
Vertical displacement — you can check this yourself
Joint condition — you can check this yourself
Age and history — you can check this yourself

Why we say this, and when it may not apply

Cracking has several ordinary causes that have nothing to do with ground movement, and treating every crack as settlement leads to repairs aimed at the wrong thing.

What we had to assume

That the crack can be seen well enough to tell whether the two sides are at different heights.
That the observation is of the crack itself rather than of a joint doing its job.

When this may not apply

Where cracking is accompanied by clear vertical displacement, movement is a stronger possibility.
Where cracks have widened measurably over time, something is ongoing.
Where cracking appears in a pattern that follows a slope or a low point rather than the slab geometry.

What would change it

A dated measurement showing the crack has changed width or displacement over time.
A straightedge reading showing the two sides sit at different heights.
Finding the crack ignores the control joints rather than running along them.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

A new surface over concrete that is deteriorating through its depth does not address the deterioration.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

An overlay bonds to the existing surface and depends on that surface staying sound.
Deterioration continuing beneath an overlay carries the overlay with it.
The division between surface and full-depth damage is established by sounding or at an exposed edge, not from the top.

Still to establish

Whether damage is surface or full depth — partly, on your own
Finish and sealer history — partly, on your own
Freeze exposure — partly, on your own

Why we say this, and when it may not apply

Resurfacing is visually transformative, which makes it an attractive answer to problems it does not solve. The distinction between surface and full-depth deterioration is the whole question and it is not visible from above.

What we had to assume

That the depth of deterioration can be established before the work is specified.
That the existing surface is sound enough for a bond where it is intact.

When this may not apply

Where deterioration genuinely is confined to the top layer, resurfacing addresses it directly.
Where an overlay is being used for appearance on sound concrete, this concern does not arise.

What would change it

Sounding results, or an exposed edge showing how deep the deterioration goes.
Finding the surface has been coated before, which changes what will bond.
Establishing whether the freeze exposure that caused it is ongoing.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Grinding a raised edge removes the trip hazard without addressing why the edge rose.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Grinding removes material from the high side, which changes the profile and not the position.
Where the underlying movement continues, the difference in height returns.
As a hazard-removal measure specifically, it is well established and not contested.

Still to establish

Soil movement — partly, on your own
Slab thickness — partly, on your own
Reinforcement — partly, on your own
Vertical displacement — you can check this yourself

Why we say this, and when it may not apply

It is a legitimate and often sensible piece of work, and it is also frequently sold as a repair. Both things are true and a homeowner should know which they are buying.

What we had to assume

That there is enough material to remove without exposing reinforcement or thinning the section unduly.
That the hazard rather than the level is the thing being addressed.

When this may not apply

Where the movement has genuinely stopped, grinding may be the whole of the necessary work.
Where the height difference is too large, grinding cannot reach it without excessive removal.

What would change it

A dated observation showing whether the height difference is still increasing.
Establishing the thickness available at that point.
Establishing whether reinforcement sits close to the surface there.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Sealing is a preventive measure rather than a correction of existing damage.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

A sealer works by limiting what gets into the concrete, which is a preventive mechanism.
Applying it over a surface that is already deteriorating does not reverse the deterioration.
Its preventive role is not contested.

Still to establish

Finish and sealer history — partly, on your own
Whether damage is surface or full depth — partly, on your own
Freeze exposure — partly, on your own

Why we say this, and when it may not apply

Sealer is inexpensive and widely sold, and it is regularly proposed for surfaces where the deterioration has already happened. Knowing which side of that line you are on determines whether the money does anything.

What we had to assume

That the surface is sound enough for the sealer to do its job.
That the exposure the sealer protects against is actually the exposure present.

When this may not apply

On sound new concrete, sealing is straightforwardly worth considering on its own terms.
Where the surface is already deteriorating, sealing is not the first question.

What would change it

Establishing whether the surface is currently sound or already breaking down.
What has previously been applied, which affects what will adhere.
How much freeze exposure and de-icing that surface actually sees.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Sealing a joint keeps water and debris out; it does not stop the movement the joint exists to accommodate.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Control and expansion joints are placed to give movement a predictable location.
A flexible sealant excludes water and debris while still permitting that movement.
A rigid filler in a joint that needs to move transfers the movement elsewhere.

Still to establish

Joint condition — you can check this yourself
Crack activity — you can check this yourself
Freeze exposure — partly, on your own

Why we say this, and when it may not apply

Joints are widely misunderstood as flaws, and sealing them is sometimes proposed as a way of stopping movement. It is a useful piece of work described wrongly.

What we had to assume

That the joints present were placed deliberately rather than being cracks that happen to look like joints.
That the movement they accommodate is within what the sealant can follow.

When this may not apply

Where a joint has already failed structurally, sealing is not the whole of the work.
Where there are no joints at all, the movement has nowhere intended to go and that is a different conversation.

What would change it

Walking the joints and establishing which are intact, open, or filled with soil.
Whether cracking follows the joints or ignores them.
How much seasonal movement the joints are actually taking.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Slab thickness measured at one point is not thickness throughout.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Slabs are poured onto ground that is rarely perfectly level, so depth varies with the base beneath.
Perimeters are frequently thicker than the middle, sometimes deliberately.
Multiple measurements across an area routinely differ.

Still to establish

Slab thickness — partly, on your own
Subgrade and compaction
Age and history — you can check this yourself

Why we say this, and when it may not apply

A single edge measurement is often the only one available, and treating it as the thickness of the slab leads to method choices that do not hold up.

What we had to assume

That the point measured is representative enough to be worth recording at all, which it usually is.

When this may not apply

On a small slab, variation has less room to develop.
Where construction is documented and was inspected, the specified depth may be reliable.

What would change it

Additional measurements at other points.
Original construction documentation.
Whether the base beneath was level before the pour.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Whether a repair can be partial rather than full depth depends on how deep the damage goes.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

A partial-depth repair removes and replaces deteriorated material down to sound concrete.
Where deterioration reaches through the section, there is no sound concrete beneath to build on.
The boundary is established by sounding, probing or a core rather than visually.

Still to establish

Whether damage is surface or full depth — partly, on your own
Reinforcement — partly, on your own
Slab thickness — partly, on your own

Why we say this, and when it may not apply

It is the technical distinction behind two repair categories that sound similar and cost very differently, and it cannot be judged from the surface.

What we had to assume

That the extent of deterioration can be established before the work is specified rather than discovered during it.
That reinforcement position is known well enough not to be damaged in removal.

When this may not apply

Where deterioration is visibly through the section already, the question is settled.
Where the area is small enough that full-depth is simpler regardless.

What would change it

Sounding or coring results.
Reinforcement position and cover.
Whether the mechanism causing the deterioration is still active.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

New concrete continues gaining strength for weeks after it is walkable.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Strength development is a chemical process that continues well past the point the surface is hard.
It is why loading restrictions after placement exist at all.
The behaviour is not contested.

Still to establish

Use and loading — you can check this yourself
Age and history — you can check this yourself

Why we say this, and when it may not apply

It is settled material behaviour, it explains restrictions that otherwise look arbitrary, and it is the reason a slab that feels finished is not ready for a vehicle.

What we had to assume

That curing conditions were within normal ranges, since temperature and moisture affect the rate.

When this may not apply

Mixes designed for early strength behave differently and the restrictions differ with them.
Cold or very dry conditions during placement change the picture.

What would change it

What mix was used, which the contractor can state.
The conditions during and after placement.
What load is intended and when.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Photographs can establish what a condition looks like but not what caused it.

Established practice This is how the work is normally done, and it is not seriously contested among people who do it. It usually reflects material behaviour or long-standing method rather than opinion.

Evidence considered

Several distinct causes produce visually similar results.
The information that distinguishes them — movement over time, void, subgrade, thickness — is not visible in an image.
Photographs do reliably narrow the field and make an on-site visit shorter.

Still to establish

Soil movement — partly, on your own
Void depth and extent
Subgrade and compaction
Crack activity — you can check this yourself

Why we say this, and when it may not apply

Remote assessment is offered widely and it is worth being direct about what it can and cannot do. Photographs are genuinely useful — for narrowing, not for concluding.

What we had to assume

That the photographs are clear, in scale and taken from more than one angle, which materially changes how much they narrow.

When this may not apply

Where a photograph captures something conclusive on its own — an exposed break, a visible root under the slab — it can settle a specific question.
Photographs taken over time can establish change, which a single photograph cannot.

What would change it

A second set of dated photographs of the same point.
A scale reference in frame.
An exposed edge or break included in the frame.

Established practice does not mean this: It does not mean the practice is right for your property, that any particular contractor follows it, or that following it guarantees an outcome. Established practice describes what is normal, not what will happen at your address.

Strong field consensus (5)

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.

Water where it should not be is more often a symptom of something else than the problem itself.

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

Water arrives somewhere because of where it is directed and how the ground falls, both of which are upstream of the slab.
Correcting drainage frequently resolves conditions that were being attributed to the concrete.
Repairs carried out while water is still arriving have a poor record.

Still to establish

Water source — partly, on your own
Drainage — you can check this yourself
Soil movement — partly, on your own

Why we say this, and when it may not apply

Homeowners generally report the water, and the water is generally the third thing in a chain that starts with a slope, a discharge point or a leak. Fixing the visible end of the chain does not stop it.

What we had to assume

That the water has an identifiable source, which is usually but not always the case.
That the source is accessible enough to be corrected.

When this may not apply

Where the water table is genuinely high, there may be no upstream source to correct.
Where the concrete itself has failed in a way that admits water, the slab is part of the chain.
Where a plumbing leak is the source, this is not a concrete question at all.

What would change it

Establishing that wetness does not track rainfall or irrigation, which points at a leak or groundwater.
Watching where water actually goes during rain, which frequently identifies the source outright.
Meter movement with all fixtures off.

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.

Where water is contributing, correcting it first tends to protect whatever slab work follows.

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

Water contributes to several of the mechanisms that damage and move concrete.
A correction carried out while the contributing condition continues is exposed to it from day one.
Drainage work is frequently cheaper than the concrete work it protects.

Still to establish

Drainage — you can check this yourself
Water source — partly, on your own
Access — you can check this yourself

Why we say this, and when it may not apply

Sequencing is one of the few things a homeowner can influence directly, and getting it wrong is a common way for good work to fail early.

What we had to assume

That water is in fact contributing, rather than being coincidental.
That the drainage correction is within reach at reasonable cost.

When this may not apply

Where water is not part of the mechanism, sequencing this way delays the actual work.
Where a trip hazard or similar makes the concrete an immediate safety matter, that comes first.
Where the drainage correction requires the concrete to be lifted anyway, the sequence is set by access.

What would change it

Observation during rain establishing whether water actually reaches the affected area.
Establishing that the wetness does not track rainfall, which points elsewhere.
Finding the slab must come up regardless, which reorders the work.

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.

Freeze–thaw deterioration has a characteristic appearance that helps distinguish it from other surface damage.

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

The mechanism is repeated expansion of water within the concrete as it freezes, which damages the surface from just below it.
That produces a pattern of loss different from mechanical damage or from a finishing defect.
Exposure depends on how wet a surface stays and how much sun it sees, not on regional climate alone.

Still to establish

Freeze exposure — partly, on your own
Finish and sealer history — partly, on your own
Whether damage is surface or full depth — partly, on your own
Drainage — you can check this yourself

Why we say this, and when it may not apply

Surface conditions are the ones homeowners most often misattribute, and freeze–thaw is one of the few with a mechanism distinctive enough to narrow things from appearance alone.

What we had to assume

That the surface in question actually goes through freezing while wet, which varies within a single property.
That the appearance has not been altered by a coating or a previous repair.

When this may not apply

In regions where freezing is rare, other surface mechanisms are far more likely and this is not the first explanation.
Where a coating has failed, the appearance can mimic this closely.
Where de-icing salts have been used, the picture is mixed rather than clean.

What would change it

Whether that specific surface stays wet longer than the rest of the property.
What has been applied to it, including de-icer.
Whether the loss is confined to the top layer or goes deeper.

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.

Two proposals for what looks like the same job frequently differ in what is actually included rather than in price for identical work.

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

Proposals vary in whether they include removal, disposal, base preparation, reinforcement, jointing and restoration.
Access, protection and reinstatement are legitimate cost drivers that differ between contractors on the same site.
The same words are used for different amounts of work across the trade.

Still to establish

Access — you can check this yourself
Slab thickness — partly, on your own
Reinforcement — partly, on your own

Why we say this, and when it may not apply

It is the single most useful thing a homeowner can understand before comparing quotes, and it is the reason a comparison by total is usually a comparison of two different things.

What we had to assume

That both proposals are for the same physical area, which is worth checking before anything else.
That each proposal states its scope in enough detail to compare, which many do not.

When this may not apply

Where two proposals genuinely itemise the same scope, the difference is price.
Where one proposal is not specific enough to establish scope, there is nothing to compare yet.

What would change it

Each proposal stating removal, base preparation, thickness, reinforcement and restoration explicitly.
Establishing whether both are pricing the same area.
Establishing access constraints, which affect method and cost legitimately.

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.

Mixed evidence (2)

Neither polyurethane foam nor cementitious slurry lifting is the better method in general.

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

The two methods differ in material weight, injection hole size, working time and how the material behaves in wet ground.
Each has situations where its properties are an advantage and situations where they are a disadvantage.
Experienced practitioners disagree, and the disagreement does not track experience or competence.

Still to establish

Void depth and extent
Subgrade and compaction
Use and loading — you can check this yourself
Water source — partly, on your own
Access — you can check this yourself

Why we say this, and when it may not apply

Both are marketed as the modern correct answer, usually by whoever owns the equipment. The genuine differences are real but they are trade-offs rather than a ranking, and homeowners are entitled to know that the disagreement is honest.

What we had to assume

That both methods are available in the area and competently executed, which is not everywhere true.
That the choice is being made on suitability rather than on which equipment is already on the van.

When this may not apply

Where only one method is realistically available locally, the comparison is academic.
Where access limits equipment, the decision may be made by the site rather than by the merits.
Where the ground is saturated, the material properties matter more and the trade-off shifts.

What would change it

Establishing how much load the surface actually carries, which changes how much the material weight difference matters.
Establishing the moisture condition of the ground beneath.
Establishing the depth and extent of the void, which affects material volume and behaviour.

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.

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.

Site dependent (1)

A hollow sound when concrete is tapped suggests a void but does not establish one.

Site dependent There is no general answer worth giving. The right conclusion turns on conditions at your property — soil, drainage, what is under the slab, what has been done before — and those differ enough that a general rule would be misleading.

Evidence considered

Sounding is a real technique and a change in tone does indicate a change in what is beneath.
A thin section over sound base, delamination within the concrete, and an actual void can all produce a similar change.
Confirming which requires probing or drilling.

Still to establish

Void depth and extent
Slab thickness — partly, on your own
Whether damage is surface or full depth — partly, on your own

Why we say this, and when it may not apply

It is the one test homeowners can do themselves and it gets reported as conclusive. It is genuinely useful and genuinely not conclusive, and both halves matter.

What we had to assume

That the comparison is against an adjacent area of the same slab rather than against expectation.
That the surface is dry and clear enough for the difference to be audible.

When this may not apply

Over a large area of consistent tone, there is nothing to compare against and the test says little.
Where the surface is already delaminating, the tone reflects the surface rather than the base.

What would change it

Probing or a test hole establishing whether there is a gap and how deep.
Establishing the thickness at that point.
Whether the same tone appears across the whole slab or only in one area.

Site dependent does not mean this: It does not mean nothing can be known, and it is not a way of avoiding the question. It means the information that settles it is at your property rather than in an article.

Inspection required (1)

Movement in concrete that adjoins the house should be treated as a building question until somebody establishes otherwise.

Inspection required This cannot be settled without somebody qualified being present. Not because the question is difficult in principle, but because it depends on something that has to be measured, opened up, or seen in person.

Evidence considered

Slabs adjoining a building may be independent of it or tied into it, and the two look similar from above.
Where they are tied, movement in the slab is movement in the structure.
The distinction generally requires inspection at the junction and sometimes excavation.

Still to establish

What the concrete adjoins — partly, on your own
Subgrade and compaction
Soil movement — partly, on your own

Why we say this, and when it may not apply

It is the one fork in this whole subject where getting it wrong is expensive in a way that cannot be undone later, and whether a slab is independent of the foundation is frequently not visible from the surface.

What we had to assume

That the junction is accessible enough to be examined.
That the caution is worth the cost of establishing it, which for anything touching the house it generally is.

When this may not apply

Where the slab is visibly separated from the building by an open or sealed joint, the question is usually settled.
Where original construction is documented, it may be answerable from records.

What would change it

Examination at the junction establishing whether there is a separation.
Original construction documentation.
Whether movement is also visible inside the building.

Inspection required does not mean this: It does not mean the situation is serious, and it does not mean you are being pushed toward paying for an inspection. Plenty of things in this category turn out to be minor once somebody looks.

Not established (1)

We do not state what permits or local requirements apply to any specific property.

Not established We do not have a basis for a claim here. Either the question has not been settled in any way we can point to, or the honest answer is that we have not established it and are not going to guess.

Evidence considered

Permit requirements for the same work differ between adjacent municipalities.
They are amended locally and on their own schedule.
The authority with jurisdiction answers this directly and for free.

Still to establish

Local requirements — partly, on your own

Why we say this, and when it may not apply

Requirements differ between neighbouring jurisdictions and change without notice. Publishing one that turned out to be wrong would be worse for a homeowner than publishing nothing, and there is a correct place to ask.

What we had to assume

That the homeowner can identify which authority has jurisdiction, which is occasionally not obvious.

When this may not apply

A contractor who works in that jurisdiction routinely will usually know, and can be asked.

What would change it

Nothing we could publish. This is answered by the authority with jurisdiction over the property, not by a website.

Not established does not mean this: It does not mean the answer is unknowable or that nobody knows. It means *we* do not have grounds to tell you, and saying so is more useful than filling the space.

What keeps coming up

Across those 20 records the same pieces of information keep being the thing still to establish. That repetition is worth noticing: it is a fair picture of what somebody qualified is actually trying to find out when they look at concrete, and there are only 20 of them in total.

The order below is counted from the records rather than chosen by us.

Slab thickness — open in 6 of our 20 records; partly within your reach
Soil movement — open in 6 of our 20 records; partly within your reach
Subgrade and compaction — open in 6 of our 20 records
Whether damage is surface or full depth — open in 6 of our 20 records; partly within your reach
Void depth and extent — open in 5 of our 20 records
Crack activity — open in 4 of our 20 records; you can establish this yourself
Freeze exposure — open in 4 of our 20 records; partly within your reach
Access — open in 3 of our 20 records; you can establish this yourself
Age and history — open in 3 of our 20 records; you can establish this yourself
Drainage — open in 3 of our 20 records; you can establish this yourself
Finish and sealer history — open in 3 of our 20 records; partly within your reach
Reinforcement — open in 3 of our 20 records; partly within your reach
Water source — open in 3 of our 20 records; partly within your reach
Joint condition — open in 2 of our 20 records; you can establish this yourself
Use and loading — open in 2 of our 20 records; you can establish this yourself
Vertical displacement — open in 2 of our 20 records; you can establish this yourself
What the concrete adjoins — open in 2 of our 20 records; partly within your reach
Local requirements — open in 1 of our 20 records; partly within your reach
Previous repairs — open in 1 of our 20 records; you can establish this yourself
Trees and roots — open in 1 of our 20 records; partly within your reach

Why this matters

Because it lets you judge the advice instead of trusting the tone. A confident paragraph and a careful one look similar, and the difference between them is not visible in the writing. Here it is written down.

What homeowners commonly misunderstand about this

That a grading is a probability. It is not. There is no number behind any of these states, and if we gave you one it would be invented.
That “established practice” means it applies to you. It means the practice is normal. Whether it fits your property is a separate question and usually a site-dependent one.
That a contractor contradicting a graded claim is wrong. Frequently they are looking at something we cannot see. The grading tells you whether their answer is worth a follow-up question, not whether it is right.
That this replaces an inspection. Two of the six states exist specifically to say it does not.

Questions to ask next

Which of the things still to establish apply to my concrete, and which of those can I establish myself before anybody visits?
When a contractor makes a recommendation, what would have to be true for them to change it?
Which parts of their proposal depend on something nobody has measured yet?

Information still needed

Ours, not yours: the sources behind several of these claims are not yet verified to the standard we set for publishing a citation, and until they are, they stay hidden rather than being shown as support. What you see on an evidence card is the reasoning, and where a verified source exists it is listed. Where none is listed, none has been verified.

Nothing here is an inspection, a diagnosis, or a substitute for somebody qualified looking at your property. When you are ready, we will help connect you with a contractor who can evaluate your specific situation — and we will tell you plainly if we cannot.

Next: what we cannot tell you from here, the terms and the 20 things a professional establishes, and how to record what you have.