Concrete · Service

Concrete installation, and where it will crack

Concrete cracks. That is not a defect, it is a material property. A good pour decides where the cracks go and keeps them tight and invisible. A bad one lets the slab choose.

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In short

What is concrete installation?

Concrete installation is the forming, pouring, finishing and curing of a slab — a driveway, patio, walkway, garage or shed pad. Most of the work happens before the truck arrives: excavating, compacting a base and setting forms to a drainage fall. Concrete shrinks as it cures and it will crack somewhere. Control joints are how the installer chooses where, and curing is what determines how strong the surface ends up.

Triggers

Signs you need concrete installation

The existing slab has cracks wide enough to catch a heel or wide enough for weeds
The surface is flaking, pitting or shedding a sandy layer — the top has lost its integrity
Sections have sunk or heaved so panels no longer meet flush
Water pools on the slab or runs toward the house instead of away from it
You are adding something new — a patio, a garage pad, a walkway, an equipment slab
A slab is cracked in a spiderweb pattern across most of its area rather than in one line
Reinforcement is visible and rusting where the surface has broken away

Seeing something not on this list? Browse concrete problems by symptom →

The job

How concrete installation actually works

Layout, excavation and drainage planning

The area is marked out and dug to depth, and the fall is set so water leaves the slab and moves away from the building. On a driveway that fall has to work with the street and the garage threshold at the same time.

Watch for: No slope designed in, or slope running toward the house. Water directed at a foundation by a new slab is a far more expensive problem than the slab it came with.
Base preparation and compaction

A layer of crushed aggregate is placed and mechanically compacted in lifts. This is what actually carries the load — the slab spreads it, the base supports it. Soft or organic soil is dug out rather than built on.

Watch for: Base material dumped and raked rather than compacted with a plate or roller, and compaction done in one thick layer instead of several. Uncompacted base settles under load, and a slab bridging a void cracks in a way no amount of thickness prevents.
Forms, thickness and reinforcement

Forms are set to line and grade, then reinforcement — wire mesh or rebar on chairs — is positioned so it sits within the slab rather than on the ground. Thickness is specified for the load: a walkway and a slab that will carry a vehicle are not the same.

Watch for: Mesh laid on the base and "pulled up" during the pour. It rarely ends up where it should, which means it is doing nothing. Reinforcement supported on chairs before the pour is visible on site and easy to check.
Ordering the right mix

The concrete is specified for the job — strength, and in freezing climates an air-entrained mix, which builds microscopic air voids that give freezing water somewhere to expand into.

Watch for: Water added to the truck at the site to make the mix easier to work. Extra water makes placement faster and the finished concrete measurably weaker and more prone to surface failure. It is the most common corner cut in the trade, and it happens in front of you.
Placing, screeding and floating

Concrete is placed, struck off level with a screed, then floated to bring a workable surface up. Bull floating happens early; further finishing waits until bleed water has left the surface.

Watch for: Finishing worked while bleed water is still standing. Working that water back into the surface is a direct cause of the thin, weak top layer that flakes away a few winters later.
Final finish and edging

The surface is given its texture — a broom finish for traction outdoors, a smoother trowel finish inside a garage — and edges are tooled so they do not chip.

Watch for: A slick trowelled finish on an exterior slab. It looks good on handover and is genuinely slippery when wet or icy. Broom finish exists for a reason.
Cutting control joints

Joints are cut or tooled to a depth that creates a deliberate weak line, spaced according to slab thickness, so shrinkage cracking happens along them rather than randomly. Timing matters — too late and the slab has already cracked on its own.

Watch for: Joints too shallow, spaced too far apart, or cut a day later. Any of the three and the slab cracks where it wants to. A cracked panel between correctly cut joints is a different conversation from a crack across the middle of an uncut slab.
Curing

Concrete gains strength through a chemical reaction that needs moisture, not through drying out. Curing means keeping moisture in — a curing compound, plastic sheeting, or wetting — for a period after the pour.

Watch for: A slab left to dry in the sun and wind with nothing on it. It will be walkable on schedule and permanently weaker at the surface than it should have been, and there is no fixing that later.

Money

What does concrete installation cost?

Flatwork is normally priced per square foot, with thickness, reinforcement, access for the truck, and how much excavation and base work is needed driving the spread. Removing an existing slab is a separate line. Decorative finishes cost considerably more than a broom finish. See the Cost Guide.

See the full concrete installation cost guide — by material, size and region →

Straight answer

When concrete installation is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

The ground underneath has not stopped moving. Poor drainage, a settling trench where a service was run, or fill that has not consolidated will crack a new slab the same way it cracked the old one. Fix the ground first — that is the actual repair.
You want a perfectly uniform, crack-free surface indefinitely. No slab delivers that. Hairline shrinkage cracking and colour variation are normal in a correctly built pour. If the appearance standard is that high, pavers let you replace individual units instead.
You are pouring in the wrong weather and cannot wait. Concrete placed in freezing conditions without protection, or in extreme heat without measures to slow surface drying, comes out weaker at the surface. If the schedule cannot flex, that risk should be priced and discussed rather than ignored.
Access will not take a truck and the pour is large. Where a ready-mix truck cannot reach, concrete gets pumped or barrowed, both of which add real cost. On a small area, another material may simply make more sense.
Utilities, a septic field or tree roots sit under the area. Slabs over services mean breaking concrete to reach them later, and mature roots will lift a slab over time. Plan around them or accept the future cost knowingly.
The existing slab is sound but sunken. If the concrete itself has no significant cracking or surface failure and has simply dropped, lifting it costs a fraction of replacement.

Your options

Types of concrete installation

Mix, reinforcement and sealers

Ready-mix, rebar, wire mesh, control joints and sealers, explained properly.

Concrete vs pavers

The genuine head-to-head for driveways and patios, including repairability.

Thickness and planning guides

Slab thickness by use, driveway planning and freeze-thaw care.

Compare concrete options side by side →

Straight answer

Can I do this myself?

Reasonable to DIY

Small, low-stakes pours — a shed pad or a post base — with bagged mix, accepting a home-grade finish
Excavating and removing spoil ahead of a contractor
Sealing a cured slab as ongoing maintenance, with the product the installer recommends
Keeping a new slab wet or covered during the curing window, if the contractor asks you to

Call a licensed pro

Anything a vehicle will drive on. Thickness, base and reinforcement all have to be right together
Any pour large enough to need a ready-mix truck, because placement and finishing are time-limited once it arrives
Finishing itself — the window between too wet and too stiff is short and unforgiving
Joint cutting, which has to happen at the right depth within the right window
Anything structural, or anything against or supporting a foundation

Before you sign

What to check when hiring for concrete installation

How thick will the slab be, and what reinforcement, for this use?

A vehicle slab and a walkway are different specifications. A contractor who quotes one thickness for everything is quoting a habit.
How are you preparing and compacting the base, and in how many lifts?

The answer separates the contractors whose slabs last from the ones whose slabs settle. Compaction in lifts is the phrase you want to hear.
What mix are you ordering, and is it air-entrained?

In any climate that freezes, this matters directly to whether the surface survives winters.
How will reinforcement be supported during the pour?

On chairs, before the concrete arrives. "We pull it up as we go" means it will end up on the bottom doing nothing.
Where will the control joints go, how deep, and when will you cut them?

Spacing, depth and timing. Getting a specific answer tells you they are planning the cracking rather than hoping.
How will you cure it, and for how long?

Curing is invisible and free to skip. Naming a method and a duration is a good sign.
Which way does water run when you are finished?

Away from the house. Ask to see it on the plan before the forms go in, not after the pour.
Is removal and disposal of the existing slab included?

Broken concrete is heavy and disposal is priced by weight. It is a common exclusion.

All concrete hiring checklists →

Local pros

Concrete Installation near you

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Related work

Often done at the same time

Driveway Installation

The vehicle-rated version of this work

Concrete Repair

When the slab can be saved

Concrete Leveling

Lifting a sound slab that has sunk

Concrete Demolition

Getting the old slab out

All concrete services →

FAQ

Concrete Installation — questions people ask

Still have a question? Talk to our team →

How long before I can walk on and drive on new concrete?

Light foot traffic is usually possible within a day or so, but vehicles need considerably longer — concrete continues gaining strength for weeks after it is hard enough to touch. Ask your contractor for both dates specifically, because driving on a slab early is one of the few homeowner actions that can damage an otherwise good pour permanently.

Why did my new concrete crack?

Some cracking is inherent — concrete shrinks as it cures and the shrinkage has to go somewhere. The question is whether it went where it was supposed to. Cracks that follow control joints are the system working. Random cracks across a panel usually mean joints were too shallow, too far apart or cut too late, the base settled, or too much water went into the mix.

What are control joints and why do they matter?

They are deliberate grooves cut or tooled partway through the slab, creating a plane of weakness so shrinkage cracking follows the line instead of wandering across the surface. The crack still happens — it happens down inside the joint where you cannot see it. Depth and spacing are both governed by slab thickness, which is why "we cut some joints in" is not an adequate answer.

Does concrete need to be sealed?

In freeze-thaw climates and anywhere de-icing salts are used, sealing is worthwhile protection for the surface, and it is reapplied periodically rather than once. In mild climates it is more about appearance and stain resistance. Ask which product and when the first application should happen — sealing too early, before the slab has cured, causes its own problems.

What causes concrete to flake and pit at the surface?

Usually a weak surface layer, and the two common causes are too much water in the mix and finishing worked while bleed water was still on the surface. Freeze-thaw cycling and de-icing salts then attack that weakened layer. Air-entrained mix, proper finishing timing and curing are the defences, and all three are decided on pour day, not afterwards.

Can new concrete be poured over an existing slab?

Sometimes, as a bonded or unbonded overlay, but it needs the existing slab to be structurally sound and it adds height that has to work with thresholds and drainage. Where the old slab is cracked because the base under it failed, an overlay reproduces the failure and adds weight to it. Removal is often the honest answer even though it is the expensive one.