Tarmac ages in three separate ways and people tend to blame all of them on dirt. The surface goes grey as the bitumen oxidises. It grows moss and algae, especially along the shaded edges. And it develops cracks, crumbling and potholes as the base beneath moves or water gets in.
Only the second of those is a cleaning problem. Recognising which of the three you actually have is the difference between a job that transforms the drive and a job that disappoints. This guide walks through all three, in the order you should tackle them.
Assess before you clean
- Walk the drive and mark cracks wider than a hairline; those need sealing before winter regardless of appearance.
- Press suspicious soft patches — a spongy or depressed area suggests fuel damage or base failure, not dirt.
- Check the edges for crumbling, which is nearly always a restraint problem.
- Note where water stands, and how long after rain it takes to clear.
- Look at the colour in a sheltered spot versus an exposed one; the difference tells you how much of the greyness is oxidation.
- Look for a spider-web pattern of fine cracking, which indicates the base is fatiguing under load.
Cleaning tarmac without damaging it
Tarmac holds together through the bitumen binding its aggregate, and excessive pressure strips the fines from the surface. Once you have scoured a patch, it is visibly rougher and paler than its surroundings permanently. So the method leans heavily on chemistry and much less on force.
Apply a biocide across the whole surface and give it a full dwell. Moss on tarmac often has a surprisingly strong hold, and killing it properly means it lifts off rather than needing to be scraped away.
Wash with a rotary flat-surface cleaner at moderate pressure, keeping constant movement. Never hold a lance close and static, and never use a turbo nozzle. Work in full runs so there are no visible seams, and rinse thoroughly.
The result should be a uniform, moss-free, clean-looking surface. It will still be grey. That is the correct outcome, not a failure of the clean.
Repairs: cracks, potholes and edges
Cracks are the priority because they are how water gets into the base, and water in the base is how potholes are born. Clean the crack out, then fill with a bitumen-based crack sealant. Doing this in late summer, before the wet season, prevents a great deal of winter damage.
Potholes need cutting back to sound material with square edges, cleaning out, priming and filling with a proper cold-lay or hot-lay material, then compacting. A shovel of loose material tipped into a hole and driven over will be back out within weeks.
Crumbling edges usually mean there was never adequate restraint. Installing a haunched kerb or edging along the affected side stops the erosion continuing. Patching the edge without adding restraint simply gives the same problem a new date.
Colour restorers: an honest assessment
- A bitumen-based restorer is a coating that recolours the surface to black. It genuinely transforms appearance in a way cleaning cannot.
- It is a coating with a maintenance cycle, not a permanent repair — expect to reapply on a rolling basis.
- It must go onto a clean, dry, sound surface, so the cleaning stage is still required first.
- It will not fix cracks, potholes or soft patches; those must be repaired before application.
- Applied over a failing surface, it briefly disguises problems and then fails along with them.
- Some products can be slippery when first applied, so grip on slopes is worth checking.
Fuel and oil damage is a special case
Diesel and petrol dissolve bitumen. A drive with a history of fuel drips under a parked vehicle will show a softened, sunken, sometimes tacky patch, and that patch is chemically damaged rather than dirty.
No amount of cleaning brings it back, and a colour restorer applied over it will not adhere reliably. The honest repair is to cut out the affected area and patch it, then keep future drips off the surface with a drip tray if the vehicle is a known offender.
Catching a fresh spill quickly with absorbent granules, before it soaks in, is the only real prevention.
Drainage: the thing that decides how long it lasts
Almost every tarmac failure has water somewhere in its history. Water sitting on the surface promotes moss, works into hairline cracks, and freezes and expands in winter. Water getting into the base softens it until the surface above deforms.
So before spending on cleaning or coating, deal with the drainage. Clear the gullies, make sure the falls actually take water somewhere, and fix the low spot that always holds a puddle. A drive that drains properly will outlast an identical one that does not by a considerable margin.
When restoration is no longer the right answer
If the drive shows extensive web-like cracking across large areas, multiple potholes, or a surface that flexes underfoot, the base has failed. Surface work is money spent on a problem that lives underneath it.
A useful test is proportion: if you are repairing more than a modest fraction of the total area, an overlay or full replacement is likely to be better value than a series of patches that will each need revisiting.
We would rather tell you that up front than clean a drive that needs digging up.