Tarmac Driveway Cracking And Crumbling

What's happening?

Tarmac is a flexible surface: a bitumen-bound wearing course carried by a compacted sub-base. It fails at the top or from below, and the pattern tells you which. Fine cracks in a network, with a grey, dry-looking surface, are the binder oxidising after years of sun and rain, which is a surface-life problem. Cracks that follow a line, an edge or a wheel path, with a dip alongside, mean the base is moving under load. Crumbling at the perimeter means there is no restraint and the edge has nothing to lean on. Ruts and shiny depressions where a car parks are the layer being too thin or laid at the wrong temperature. Once water reaches the base through a crack, frost widens it every winter.

What usually causes it?

• Binder oxidising with age, leaving a dry, brittle surface that cracks in a network
• A sub-base too thin or poorly compacted for vehicle loads, giving cracks along the wheel paths
• Unrestrained edges with no kerb, block edging or haunching, so the perimeter crumbles away
• Tarmac laid too thin, laid cold, or rolled after it had cooled, so it never compacted properly
• Water entering an existing crack and frost widening it each winter
• Fuel, oil or diesel spills dissolving the bitumen and softening the surface in patches
• Tree roots lifting the surface, or a settled service trench opening a straight crack

Is it dangerous?

Not an immediate hazard, but a crumbling edge and an open crack are both trip risks, and a rut holds water that freezes. The real issue is speed of decline. Tarmac depends on being sealed: as soon as water gets to the base through a crack, the base softens, the surface flexes more, and the crack grows. A drive left through two or three winters with open cracks usually needs more than a surface repair by the end of it. Softening from a fuel spill spreads as long as the contamination remains.

Can I fix it myself?

Read the pattern before deciding anything. Photograph the cracks and note whether they are a fine network across the whole drive, straight lines, or confined to wheel paths and edges. Press a screwdriver into a crumbling edge to see whether it is only the surface or the base beneath as well. Keep the cracks clear of soil and weeds, and brush loose material out so water is not held in them. Cold-lay repair material will close a small isolated crack or pothole for a while and is a reasonable stop-gap before winter. It will not fix a moving base, an unrestrained edge or a surface that has reached the end of its life.

When should you call a driveway and patio installer?

Call a driveway specialist when cracks run in lines rather than a network, when the edges are breaking up, when there are ruts or soft patches where the car stands, or when a pothole has gone through to the stone below. Those are base and thickness faults and patching them repeatedly costs more than dealing with them once. Get a fuel or oil spill assessed rather than surfaced over, since the contamination keeps attacking the bitumen underneath.

What will the driveway and patio installer actually do?

• Inspect the crack pattern and core or excavate to establish the layer thicknesses and the state of the sub-base
• Identify whether the fault is surface ageing, base movement, edge restraint or contamination
• Excavate and rebuild the sub-base in compacted layers where the base has failed, rather than overlaying a moving one
• Cut out contaminated or crumbling areas back to sound material before resurfacing
• Install a proper edge (kerb, block edging or haunching), so the perimeter is restrained
• Lay and roll the new surfacing to the correct thickness and falls while it is at working temperature

Who fixes this

• Driveway repair
• Tarmac driveway

Questions people ask

Sources & References

1. Building Regulations: Approved Document H (drainage and waste disposal)
2. GOV.UK: Guidance on the permeable surfacing of front gardens
3. RoSPA: Garden safety advice