Learning centre
Concrete terms, and what a professional is trying to establish
Two vocabularies. The first is the 20 pieces of information a conclusion about concrete actually turns on — what somebody qualified is trying to find out when they walk around your property. The second is the 22 words they will use while doing it.
Knowing the words matters more than it sounds like it should. A homeowner who does not know what a control joint is cannot ask why one is missing, and somebody who thinks spalling and scaling are the same word cannot tell whether two proposals describe the same condition.
What a professional is trying to establish
Ordered by how often each one turns out to be the open question across the claims we publish, counted rather than chosen. The first few are the ones worth understanding if you only read part of this.
18 of the 20 are things you can establish or partly establish without anybody visiting.
Slab thickness
Partly within your reach Open in 6 of the claims we publish.
How thick the concrete actually is, which is often not what was specified.
Why it matters
It affects what the slab can carry, how it cracks, and whether some repair methods are viable at all.
How it gets established
Measuring at an exposed edge, a core, or a drilled hole. An exposed edge is the cheapest and is sometimes already available.
What you can do: If any edge is exposed — at a joint, a break, or where the slab meets a drain — photograph it with a tape or a coin against it. Do not break concrete to find out.
Commonly misread: Thickness at one edge is not thickness throughout. Slabs are routinely thinner in the middle than at the perimeter.
Where this comes up: Lifting methods depend on the slab being sound enough to move as a unit; Grinding a raised edge removes the trip hazard without addressing why the edge rose; A hollow sound when concrete is tapped suggests a void but does not establish one.
Soil movement
Partly within your reach Open in 6 of the claims we publish.
Whether the ground under and around the concrete is moving, and if so in which direction and in response to what.
Why it matters
Concrete rarely fails on its own. Most of what looks like a concrete problem is the ground beneath it doing something, and a repair that ignores the movement gets undone by it.
How it gets established
Repeat elevation readings over time, soil type for the area, and evidence of what the ground has done to nearby structures, fences and paving. A single visit shows position; two visits apart show movement.
What you can do: Mark and date the position of an edge or a gap and look again after a wet spell and after a dry one. Two dated observations are worth more than one careful description.
Commonly misread: Movement that has stopped and movement that is ongoing produce the same photograph. Only time distinguishes them.
Where this comes up: Lifting methods depend on the slab being sound enough to move as a unit; Water where it should not be is more often a symptom of something else than the problem itself; Grinding a raised edge removes the trip hazard without addressing why the edge rose.
Subgrade and compaction
Needs somebody on site Open in 6 of the claims we publish.
What the slab was placed on, and whether it was compacted properly before the pour.
Why it matters
Poor compaction produces settlement years later that looks identical to settlement from any other cause, and it changes whether a repair addresses the reason or just the result.
How it gets established
Excavation or test holes at the edge, sometimes original construction records where they survive. Frequently it is inferred from the pattern of movement rather than observed directly.
Commonly misread: Original construction quality is often assumed to be unknowable. The pattern and timing of movement frequently narrow it considerably.
Where this comes up: Concrete that is uneven does not automatically need replacing; Neither polyurethane foam nor cementitious slurry lifting is the better method in general; A tree near displaced concrete is not by itself evidence that roots caused it.
Whether damage is surface or full depth
Partly within your reach Open in 6 of the claims we publish.
Whether deterioration is confined to the top layer or goes through the section.
Why it matters
It is the main division between resurfacing-type work and replacement-type work, and it is not reliably visible from above.
How it gets established
Sounding, probing at a broken edge, or a core. Sometimes evident where a piece has already come away.
What you can do: Where material has already come loose, photograph the exposed edge so the depth is visible. Do not chip at sound concrete to find out.
Commonly misread: Extensive surface damage looks worse than a small full-depth failure and is often much less consequential.
Where this comes up: Concrete that is uneven does not automatically need replacing; A new surface over concrete that is deteriorating through its depth does not address the deterioration; Sealing is a preventive measure rather than a correction of existing damage.
Void depth and extent
Needs somebody on site Open in 5 of the claims we publish.
Whether there is a gap between the underside of the slab and the material beneath it, how deep, and over how much of the area.
Why it matters
It is the difference between a slab that is unsupported and one that is merely uneven, and it determines whether lifting has anything to push against.
How it gets established
Probing, sounding, or drilling test holes. In some cases ground-penetrating survey. All of it requires equipment and access to the slab.
Commonly misread: A hollow sound when tapped is suggestive but not conclusive — several other things produce it, including a thin section over sound base.
Where this comes up: Concrete that is uneven does not automatically need replacing; Lifting methods depend on the slab being sound enough to move as a unit; Neither polyurethane foam nor cementitious slurry lifting is the better method in general.
Crack activity
You can establish this yourself Open in 4 of the claims we publish.
Whether a crack is still moving — opening, closing seasonally, or displacing vertically — or has been stable for years.
Why it matters
An active crack and a dormant one of identical appearance call for different work, and repairing an active one as though it were dormant is a common way to waste money.
How it gets established
Dated measurement of the same point over time, sometimes with a fixed gauge across the crack. Two readings in different seasons are far more informative than one.
What you can do: Draw a line across the crack, write the date beside it, and photograph it. Repeat in a few months. This costs nothing and answers a question nobody can answer from a single photo.
Commonly misread: Width is treated as severity. A wide dormant crack is often less consequential than a narrow one that is still moving.
Where this comes up: Lifting methods depend on the slab being sound enough to move as a unit; A crack does not on its own establish that anything has settled; Sealing a joint keeps water and debris out; it does not stop the movement the joint exists to accommodate.
Freeze exposure
Partly within your reach Open in 4 of the claims we publish.
How often the concrete goes through freezing and thawing while wet, which depends on climate, orientation and drainage together.
Why it matters
Freeze–thaw damage has a characteristic appearance and a mechanism that other causes do not share, so establishing exposure narrows the surface conditions considerably.
How it gets established
Regional climate records combined with how wet that particular surface actually gets and how much sun it sees.
What you can do: Note whether the affected area stays wet longer than the rest, and whether it is shaded. A north-facing slab that holds water behaves differently from a south-facing one that dries.
Commonly misread: Regional climate is treated as the whole answer. Two surfaces on the same property can have very different exposure.
Where this comes up: A new surface over concrete that is deteriorating through its depth does not address the deterioration; Sealing is a preventive measure rather than a correction of existing damage; Sealing a joint keeps water and debris out; it does not stop the movement the joint exists to accommodate.
Access
You can establish this yourself Open in 3 of the claims we publish.
Whether equipment, material and spoil can physically get to and from the work, and what is in the way.
Why it matters
Access changes which methods are practical and is one of the largest legitimate reasons two proposals for the same work differ. It is not a detail.
How it gets established
Measuring the narrowest point on the route, and noting gates, steps, slopes and overhead obstructions.
What you can do: Measure your narrowest gate or gap and photograph the route from the street. Mention anything that has to be protected or moved.
Where this comes up: Neither polyurethane foam nor cementitious slurry lifting is the better method in general; Where water is contributing, correcting it first tends to protect whatever slab work follows; Two proposals for what looks like the same job frequently differ in what is actually included rather than in price for identical work.
Age and history
You can establish this yourself Open in 3 of the claims we publish.
When the concrete was placed, what has happened to it since, and when the problem was first noticed.
Why it matters
Timing separates whole categories of cause. Something appearing in the first year points somewhere quite different from something appearing after fifteen.
How it gets established
Owner recollection, property records, previous invoices, and dated photographs — including ones taken for unrelated reasons.
What you can do: Write down your best estimate of when it was poured and when you first noticed the problem, and look through old photos of the house. Holiday photographs regularly settle this.
Commonly misread: "It has always been like that" and "it happened gradually" are frequently the same situation described differently, and they lead to opposite conclusions.
Where this comes up: A crack does not on its own establish that anything has settled; Slab thickness measured at one point is not thickness throughout; New concrete continues gaining strength for weeks after it is walkable.
Drainage
You can establish this yourself Open in 3 of the claims we publish.
Where water goes when it lands on or near the concrete, including roof water, irrigation and run-off from higher ground.
Why it matters
Water is behind a large share of concrete problems, and it is the one contributing condition a homeowner can often change. A repair carried out while water is still arriving tends not to last.
How it gets established
Watching where water actually goes during rain or with a hose, tracing downspout discharge, and looking at the fall of the ground away from the slab.
What you can do: Go out during heavy rain and watch. Photograph where water pools, where it runs and where downspouts discharge. This is the single most useful thing most owners can do.
Commonly misread: Standing water is often read as the problem. It is more often the symptom of a slope or a discharge point, and the slab is the third thing in the chain rather than the first.
Where this comes up: Water where it should not be is more often a symptom of something else than the problem itself; Where water is contributing, correcting it first tends to protect whatever slab work follows; Freeze–thaw deterioration has a characteristic appearance that helps distinguish it from other surface damage.
Finish and sealer history
Partly within your reach Open in 3 of the claims we publish.
How the surface was finished originally and what has been applied to it since — sealers, coatings, de-icing salts.
Why it matters
Several surface conditions trace to finishing or to what was put on afterwards, and a coating over a surface that is still deteriorating traps the problem rather than fixing it.
How it gets established
Owner recollection, product records, and the appearance of the surface itself.
What you can do: List anything applied to the surface, including de-icer, and roughly when. Photograph any patchy sheen or peeling.
Where this comes up: A new surface over concrete that is deteriorating through its depth does not address the deterioration; Sealing is a preventive measure rather than a correction of existing damage; Freeze–thaw deterioration has a characteristic appearance that helps distinguish it from other surface damage.
Reinforcement
Partly within your reach Open in 3 of the claims we publish.
Whether there is steel or fibre in the slab, of what kind, and where it sits within the depth.
Why it matters
It changes how cracks behave, whether pieces stay together when they move, and whether a partial repair can be tied into what is there.
How it gets established
Visible at a break or a core, detectable with a cover meter, or occasionally recorded in construction documents.
What you can do: If concrete has already broken and reinforcement is visible, photograph it. Do not create a break to look.
Commonly misread: Reinforcement is widely assumed to prevent cracking. It is mostly there to control what a crack does after it forms.
Where this comes up: Grinding a raised edge removes the trip hazard without addressing why the edge rose; Two proposals for what looks like the same job frequently differ in what is actually included rather than in price for identical work; Whether a repair can be partial rather than full depth depends on how deep the damage goes.
Water source
Partly within your reach Open in 3 of the claims we publish.
Where water reaching the concrete is coming from — roof, ground, irrigation, a plumbing leak, or below.
Why it matters
The correction is completely different for each, and some of them are not concrete work at all. A slab repair carried out over a leaking supply line is money spent on the wrong trade.
How it gets established
Observation during and after rain, isolating irrigation, checking meter movement with fixtures off, and sometimes leak detection.
What you can do: Note whether the wetness tracks rainfall, irrigation, or neither. Wetness that ignores the weather is worth investigating before anybody quotes concrete work.
Where this comes up: Neither polyurethane foam nor cementitious slurry lifting is the better method in general; Water where it should not be is more often a symptom of something else than the problem itself; Where water is contributing, correcting it first tends to protect whatever slab work follows.
Joint condition
You can establish this yourself Open in 2 of the claims we publish.
Whether the control and expansion joints are intact, sealed, filled with debris, or absent.
Why it matters
Joints are where movement is supposed to happen. When they stop working, movement appears somewhere it was not intended to, and that is often what gets reported as a crack.
How it gets established
Visual inspection along every joint line.
What you can do: Walk every joint and photograph any that are open, filled with soil, or have lost their sealant. This is quick and it is frequently where the answer is.
Commonly misread: A crack that runs along a joint is often not a failure at all. A crack that ignores the joints is more interesting.
Where this comes up: A crack does not on its own establish that anything has settled; Sealing a joint keeps water and debris out; it does not stop the movement the joint exists to accommodate.
Use and loading
You can establish this yourself Open in 2 of the claims we publish.
What actually goes on the concrete — vehicle weights, delivery traffic, equipment, or foot traffic only.
Why it matters
A slab adequate for cars can fail under a delivery lorry, and load history explains cracking that otherwise looks like a material problem.
How it gets established
Owner knowledge of what uses the surface and how often.
What you can do: Say plainly what goes on it, including the occasional heavy thing. A skip delivery two summers ago is relevant and is exactly the kind of detail people leave out.
Where this comes up: Neither polyurethane foam nor cementitious slurry lifting is the better method in general; New concrete continues gaining strength for weeks after it is walkable.
Vertical displacement
You can establish this yourself Open in 2 of the claims we publish.
Whether the two sides of a crack or joint are at different heights, and by how much.
Why it matters
Displacement means something has moved rather than merely shrunk, which changes the range of causes and the repair options.
How it gets established
A straightedge across the crack, or a level, with the difference measured against it.
What you can do: Lay something rigid and straight across the crack and photograph the gap under it, with a tape or a coin in frame for scale.
Where this comes up: A crack does not on its own establish that anything has settled; Grinding a raised edge removes the trip hazard without addressing why the edge rose.
What the concrete adjoins
Partly within your reach Open in 2 of the claims we publish.
What the slab meets — a foundation, a garage, a step, a wall — and whether the two are connected or independent.
Why it matters
It determines whether movement is a paving question or a building question, and that is the most consequential fork in the whole process.
How it gets established
Inspection at the junction, sometimes excavation. Whether a slab is tied to a foundation is often not visible from the surface.
What you can do: Photograph where the concrete meets the building, close enough to see whether there is a gap, a sealed joint, or a continuous pour.
Commonly misread: Concrete that touches the house is assumed to be part of the house. Most of the time it is not, which is good news.
Where this comes up: Concrete that is uneven does not automatically need replacing; Movement in concrete that adjoins the house should be treated as a building question until somebody establishes otherwise.
Local requirements
Partly within your reach Open in 1 of the claims we publish.
What the relevant authority requires for this work — permits, inspections, setbacks, specification.
Why it matters
It affects cost, timeline and sometimes whether the work is permitted at all, and it varies enough between neighbouring jurisdictions that no general statement is safe.
How it gets established
Asking the authority that has jurisdiction over the property, or a contractor who works in that jurisdiction routinely.
What you can do: Ask your own municipality directly. We deliberately do not publish permit requirements for any location, because getting one wrong would be worse than not answering.
Where this comes up: We do not state what permits or local requirements apply to any specific property.
Previous repairs
You can establish this yourself Open in 1 of the claims we publish.
What has already been done to this concrete, by whom, and when.
Why it matters
A previous repair changes what is physically there, and a repair that failed is evidence about the cause. It is also the thing most often left out of a description.
How it gets established
Owner knowledge, invoices, and visible differences in colour, texture or joint pattern.
What you can do: Find any paperwork and photograph the patched areas. If a previous repair did not hold, say so — it is useful information, not an embarrassment.
Commonly misread: Owners often assume a failed repair reflects the contractor. Sometimes it does; often it means the underlying cause was never addressed.
Where this comes up: Concrete that is uneven does not automatically need replacing.
Trees and roots
Partly within your reach Open in 1 of the claims we publish.
What is growing near the concrete, how big, how close, and whether roots are actually under the slab.
Why it matters
Roots can lift concrete, and removing a tree can cause the ground to move as well. Both directions matter, and one is frequently overlooked.
How it gets established
Visible root position, species and mature size, and excavation where it matters. Proximity is visible; whether roots are under the slab often is not.
What you can do: Photograph what is growing nearby with the slab in frame so the distance is legible, and note anything removed in recent years.
Commonly misread: A tree near lifted concrete is assumed to be the cause. Sometimes it is; sometimes both the tree and the slab are responding to the same soil conditions.
Where this comes up: A tree near displaced concrete is not by itself evidence that roots caused it.
The words a contractor will use
Alphabetical, because that is how you will look one up. Where a term is routinely confused with another, the entry says which and how to tell them apart — those confusions are specific and predictable, and naming them works better than defining both words separately and hoping.
- Apron — also called garage apron, driveway apron, transition slab
The section of concrete immediately in front of a garage, or where a driveway meets the street.
Why it comes up. It settles more often than the rest of the driveway, because it sits where backfill was placed against the building and where every vehicle changes angle.
Discussed properly at /concrete-driveway-cost/, /concrete-settlement/.
- Bearing capacity — also called load-bearing capacity, how much the ground can carry
How much weight the ground can support without deforming. It is a property of the soil, not of the concrete.
Why it comes up. It explains why the same slab performs differently on two properties, and why adding load — a heavier vehicle, a delivery — can start a problem that was not there before.
Discussed properly at /concrete-settlement/, /concrete-replacement/.
- Control joint — also called contraction joint, saw cut, score line
A deliberate groove cut or tooled into the slab, so that when the concrete shrinks it cracks along that line instead of somewhere random.
Why it comes up. Concrete is going to crack. Control joints decide where. A slab with too few of them, or none, tends to crack where nobody wanted it to.
Commonly confused with. A crack. A crack running neatly along a straight groove is usually the joint doing its job. A crack that ignores the grooves is the more interesting one.
Discussed properly at /cracked-concrete/, /tools/crack-severity/.
- Curing — also called setting, hardening, drying
The chemical process by which concrete gains strength after it is placed. It continues for weeks after the surface is hard enough to walk on.
Why it comes up. It is why you are told to keep off it, and off it with a vehicle for considerably longer. The restriction is not the contractor being cautious for its own sake.
Commonly confused with. Drying. Concrete does not harden by drying out — it hardens by reacting with water, which is why keeping it damp early on helps rather than hurts.
Discussed properly at /concrete-replacement/, /projects/.
- Curling — also called lifting at the edges, warping
The edges or corners of a slab lifting upward because the top of the concrete has dried and shrunk more than the bottom.
Why it comes up. It produces a raised edge that looks exactly like something pushed the slab up from below, when in fact the slab pulled itself up. The distinction changes the whole approach.
Commonly confused with. Heave or root lifting. Curling is the concrete deforming; heave is the ground moving. A curled edge is usually at a joint or a corner and is often accompanied by a gap underneath.
Discussed properly at /uneven-concrete/, /trip-hazards/.
- Differential settlement — also called uneven settlement
Different parts of the same slab have settled by different amounts, so it is not just lower — it is tilted or stepped.
Why it comes up. It is what actually causes most visible damage. Concrete that sinks evenly often shows nothing at all; concrete that sinks unevenly cracks, steps and creates trip hazards.
Commonly confused with. Uniform settlement, which is usually harmless and frequently unnoticed. The damage comes from the difference, not from the depth.
Discussed properly at /concrete-settlement/, /uneven-concrete/, /trip-hazards/.
- Efflorescence — also called white staining, salt bloom, chalky deposit
A whitish deposit left on the surface when water moves through the concrete, dissolves salts, and evaporates leaving them behind.
Why it comes up. It is usually cosmetic in itself, and it is evidence that water is moving through the concrete — which is worth knowing about even when the staining is not.
Commonly confused with. Scaling and mould. Efflorescence brushes off or dissolves; a deteriorating surface does not.
Discussed properly at /poor-concrete-drainage/, /flaking-and-scaling-concrete/.
- Expansion joint — also called isolation joint
A gap, usually filled with a compressible material, that separates the slab from something else — a wall, a step, another slab — so the two can move independently.
Why it comes up. Where one is missing or has been filled with something rigid, movement gets transferred into whatever the slab is touching, which is how a paving problem becomes a building problem.
Commonly confused with. A control joint. A control joint controls cracking within one slab; an expansion joint separates one thing from another. Filling the second with rigid material defeats the point of it.
Discussed properly at /cracked-concrete/, /repairs/.
- Full-depth repair — also called cut and patch, partial replacement, section replacement
Removing an area of concrete through its entire thickness and pouring a new section in its place.
Why it comes up. It is the middle ground between patching and replacing everything, and it is the right answer when damage goes all the way through but only in places.
Commonly confused with. Partial-depth repair, which removes only the deteriorated top portion and leaves sound concrete beneath. The word 'partial' appears in both and means different things.
Discussed properly at /repairs/, /concrete-replacement/.
- Grinding — also called saw cutting a lip, shaving, levelling the edge
Removing material from the higher side of a step so the two surfaces meet flush, without moving either slab.
Why it comes up. It is often the quickest and cheapest way to remove a trip hazard. It changes the profile, not the position, and if something is still moving the step comes back.
Commonly confused with. Levelling. Grinding removes the hazard; levelling moves the slab. Both produce a flush surface on the day.
Discussed properly at /trip-hazards/, /repairs/.
- Heave — also called frost heave, lifting, upward movement
The ground beneath the concrete expanding and pushing it upward — often because water in the soil froze, sometimes because the soil itself swells when wet.
Why it comes up. It is the mirror image of settlement and it is frequently seasonal, which means a slab can rise in winter and drop back in summer. Measuring once misses that entirely.
Commonly confused with. Root lifting and curling, both of which also raise concrete. Heave tends to be seasonal and reversible; the other two are not.
Discussed properly at /guides/freeze-thaw-soil-concrete-risk/, /uneven-concrete/.
- Mix strength — also called psi, concrete grade, strength class
A specification of how strong the hardened concrete is designed to be. It appears on a proposal as a number with units.
Why it comes up. It is a legitimate difference between proposals and one a homeowner can simply ask about. We do not publish which figure your project needs, because that depends on use, exposure and local practice.
Commonly confused with. Thickness. A stronger mix in a thinner slab is not automatically better than the reverse; they are separate specifications doing different jobs.
Discussed properly at /how-to-compare-concrete-quotes/, /concrete-replacement/.
- Mudjacking — also called slabjacking, grout jacking, pressure grouting
Lifting a slab by pumping a cement-based slurry through holes drilled in it, filling the space underneath and raising the concrete.
Why it comes up. It is one of the two main lifting methods, it is usually the cheaper one, and it is the older of the two — which is why it is sometimes described as outdated by people who sell the other one.
Commonly confused with. Polyurethane foam lifting. They achieve the same thing by different means, with genuinely different trade-offs in weight, hole size and behaviour in wet ground.
Discussed properly at /mudjacking/, /polyjacking-vs-mudjacking/.
- Polyurethane foam lifting — also called polyjacking, foam jacking, polyfoam lifting
Lifting a slab by injecting a two-part polyurethane through small holes; the material expands as it reacts and raises the concrete.
Why it comes up. It is the other main lifting method, usually costs more, uses smaller holes and a much lighter material. Whether that lightness matters depends on the site.
Commonly confused with. Spray foam insulation, which is a different product entirely. Also mudjacking — see that entry for the actual comparison.
Discussed properly at /polyjacking/, /polyjacking-vs-mudjacking/.
- Reinforcement — also called rebar, wire mesh, steel, fibre
Steel bars, welded mesh or fibres embedded in the concrete to help it hold together when it cracks or is loaded.
Why it comes up. It is one of the most common places two proposals differ silently, because it is invisible once poured and it materially affects cost.
Commonly confused with. Crack prevention. Reinforcement mostly controls what a crack does after it forms rather than stopping it forming.
Discussed properly at /concrete-replacement/, /how-to-compare-concrete-quotes/.
- Resurfacing — also called overlay, topping, skim coat
Applying a new layer of cementitious material over the existing slab, bonded to it, to give a new surface.
Why it comes up. It transforms appearance for a fraction of replacement cost, which makes it attractive for problems it cannot solve. It depends completely on what is underneath staying sound.
Commonly confused with. Replacement. A resurfaced slab is the old slab with a new coat. Anything wrong below the bond line is still there.
Discussed properly at /concrete-resurfacing/, /resurfacing-vs-replacement/.
- Scaling — also called flaking, peeling, surface loss
The thin top layer of the concrete coming away over an area, leaving a rougher surface beneath but not deep holes.
Why it comes up. It is frequently traced to the finishing, to freeze exposure while wet, or to de-icing salts — which means the cause is often in the history rather than in the concrete.
Commonly confused with. Spalling, which has depth. Also normal wear: a surface that has simply been walked and driven on for twenty years is not necessarily scaling.
Discussed properly at /flaking-and-scaling-concrete/, /concrete-sealing-and-coatings/.
- Sealer — also called sealant, concrete seal, penetrating sealer
A liquid applied to hardened concrete to reduce what soaks into it. Some sit on the surface; others penetrate.
Why it comes up. It is cheap, widely sold, and preventive. Applied to a surface that is already breaking down, it does not reverse anything.
Commonly confused with. A coating, which builds a film with its own thickness and appearance. Also joint sealant, which is a different product for a different job.
Discussed properly at /concrete-sealing-and-coatings/.
- Settlement — also called sinking, subsidence, dropping
The concrete has moved downward because the ground beneath it has moved, compressed or washed away. The concrete itself may be perfectly sound.
Why it comes up. It is the usual explanation for a slab that is now lower than it was, and it is the word most often used for any downward movement whether or not that is what happened.
Commonly confused with. Shrinkage. Concrete shrinks as it cures, which produces cracking without anything sinking. Settlement usually leaves one side of a crack lower than the other; shrinkage usually does not.
Discussed properly at /concrete-settlement/, /sunken-concrete/.
- Spalling — also called popping, chipping, breaking away
Pieces of concrete breaking away from the surface, leaving pits or craters with visible depth.
Why it comes up. It looks alarming and is one of the most common reasons homeowners start looking. Whether it matters depends almost entirely on how deep it goes, which the appearance does not tell you.
Commonly confused with. Scaling. Scaling is the loss of a thin surface layer over an area; spalling is pieces coming out, leaving depth. They can share a cause and they do not share a remedy.
Discussed properly at /spalling-concrete/, /concrete-resurfacing/.
- Subgrade — also called base, sub-base, what it sits on
The prepared ground the concrete was poured onto. Usually compacted soil, gravel or crushed stone.
Why it comes up. Most concrete problems are subgrade problems wearing a concrete costume. Whether it was compacted properly before the pour determines a great deal of what happens afterwards.
Discussed properly at /concrete-settlement/, /repairs/.
- Void — also called gap under the slab, unsupported slab
An empty space between the underside of the concrete and the material that should be holding it up.
Why it comes up. It decides whether lifting methods have anything to push against, and whether the slab is unsupported or just uneven. It is also not visible from above.
Commonly confused with. A hollow sound, which suggests a void but also has several other explanations — including a thin section sitting on perfectly sound base.
Discussed properly at /voids-under-concrete/, /sunken-concrete/.
Why this matters
Because the single biggest advantage a homeowner can have in this conversation is being able to ask a specific question. “Is that spalling or scaling?” and “is that crack following a control joint?” are questions a good contractor will answer gladly and a poor one will deflect, and you cannot ask either without the words.
What homeowners commonly misunderstand about this
- That the jargon is there to exclude you. Mostly it is not — the words are precise and the precision is useful. Where a term is used vaguely, that is worth noticing on its own.
- That a longer word means a bigger problem. Efflorescence sounds far worse than settlement and is usually far less consequential.
- That knowing the terms means knowing the answer. It means you can follow the reasoning and check whether it holds together. The answer still depends on the things on the first list.
Questions to ask next
- Which of these conditions am I actually looking at, and what makes you say that rather than the one it gets confused with?
- Which of the things on the first list have you established, and how?
- Which are you assuming, and what happens if the assumption is wrong?
Information still needed
This page defines vocabulary. It establishes nothing about your concrete — the first list is precisely the set of things it cannot establish for you, which is why each entry says how it gets established instead.
Next: how to record what you can establish yourself, and what remains out of reach from here.
When you are ready, we will help connect you with a contractor who can evaluate your specific situation.