Should you seal a tarmac driveway?

Sealing tarmac gets argued about more than it should. Some contractors treat it as essential on every drive; others dismiss it as cosmetic. Both are wrong, and the honest answer depends on the surface in front of you.

What sealing genuinely does

Tarmac is stone held together by bitumen. The bitumen provides the black colour, the flexibility and the waterproofing, and it oxidises — reacting with oxygen and UV, hardening, embrittling and losing colour.

A restorative bitumen-based sealer does three real things:

• Replenishes binder at the surface, which restores the black and, more usefully, the flexibility.
• Seals fine cracks before water gets through them into the base. This is the one that saves money.
• Slows further oxidation by putting a sacrificial layer between the binder and the weather.

That is protective, not decorative. The colour is a side effect of restoring the binder.

When it is worth doing

• The surface is grey but sound — no soft spots, no interlinked cracking. This is the ideal moment and the cheapest intervention in the drive's life.
• Fine hairline cracking has started but has not opened up. Sealing now keeps water out; leaving it does not.
• The surface has gone coarse and open as binder has thinned, but the stone is still held.
• It is a commercial surface taking heavy use, where a coating system extends the resurfacing interval considerably.

When it is money wasted

• Soft or springy areas. Water is already in the base. Sealing the top changes nothing and the failure continues underneath.
• Interlinked or crocodile cracking. That is fatigue failure from loading beyond what the base supports. It is structural, and a seal is a delaying tactic at best.
• Brand new tarmac. It needs to cure and weather first — commonly several months. Sealing too early traps volatiles and can leave a soft, tacky surface.
• A drive about to be resurfaced anyway. Obvious, but people do it.

When it makes things worse

Two situations. Sealing over standing water or a damp surface traps moisture and the seal fails early, often peeling. And sealing over live moss and algae locks the growth in, where it keeps working under the coating and lifts it.

Both are preparation failures rather than problems with sealing itself, which is why the clean and the treatment matter as much as the product.

How often

For a domestic drive in this climate, expect to be looking at it again somewhere between years three and five. Sooner on a south-facing drive taking full sun, or one that gets gritted through winter. Commercial surfaces taking constant traffic want it more often.

The test is simple enough to do yourself: if the surface has gone visibly grey and coarse again, the sacrificial layer has done its job and gone.

The short version

On a structurally sound drive, sealing is one of the genuinely worthwhile maintenance jobs — not because of the colour, but because of what it keeps out. On a drive with a base problem it is the wrong spend entirely, and any contractor who will not walk your drive before quoting is not in a position to tell you which you have.