Concrete Driveway Cracking, Flaking Or Pitting

What's happening?

Paving Expert says all concrete contracts slightly during curing, which is the primary cause of small surface cracks, and that it expands and contracts with temperature when set. It says movement joints should be made in a non-reinforced slab at about 30 times the slab thickness, so every 3.0-3.6m for a 100mm slab, and notes that there are only two types of concrete: that which has cracked, and that which is about to crack. It advises avoiding de-icing salts, as they can attack the surface of concrete. It lists salt or frost damage, repairs to services and removal of damaging tree roots as the circumstances that justify a patch repair, and says a shallow repair for salt and frost damage cuts the perimeter to at least 40mm. It says there is no such thing as an invisible concrete patch repair.

What usually causes it?

• Shrinkage cracking as the concrete cured, which Paving Expert says is the primary cause of small surface cracks
• A slab with no or too few movement joints, so cracks form where they will
• Expansion and contraction with temperature once the concrete has set
• De-icing salts attacking the surface, with frost damage
• Tree roots, services or a poor sub-base moving the slab
• An old or badly mixed slab that has deteriorated at the surface

Is it dangerous?

No. Cracks and flaking are mainly cosmetic. Paving Expert says stains alone are not sufficient justification for breaking out and patching a concrete bay.

Can I fix it myself?

Avoid de-icing salts, as Paving Expert advises. For minor surface damage, a shallow repair means marking the area, sawing the perimeter to at least 40mm, chipping out the damaged concrete, cleaning and placing fresh concrete flush, which Paving Expert says can be trafficked in 3-4 days. It says this will always be visible. Hire a contractor for anything larger: Paving Expert says it may be advisable to tie new concrete to the existing with dowels. A wide or lifting crack that is growing suggests the base or a tree root is moving the slab, so have it looked at. For a new or replacement slab, the ready-mixed concrete trade body BRMCA lists a designated concrete for house drives and domestic parking and recommends the PAV2 designation where de-icing salts are likely to be frequently applied.

When should you call a driveway and patio installer?

Call a driveway contractor when cracks are wide or growing, when the slab is moving or lifting, when flaking covers a large area, or when you want a bay replaced. Tell them about any tree roots or services nearby.

What will the driveway and patio installer actually do?

• Check whether the damage is surface scaling, shrinkage cracks or structural movement
• Cut out and repair damaged surface areas with a shallow or full-depth repair
• Replace a bay where salt or frost damage, services or tree roots require it
• Add movement joints where the slab has none
• Advise on avoiding de-icing salts, on a concrete mix suited to salt exposure, and on the repair being visible

Who fixes this

• Driveway repair
• Concrete driveway installation

Questions people ask

Sources & References

1. Paving Expert: plain concrete bases
2. Paving Expert: concrete movement joints
3. Paving Expert: repairing and replacing paving
4. BRMCA: ready-mixed concrete practical guide