Cold Lay Tarmac: What It Is Good For and How to Use It
Updated: 3 days ago
Cold lay tarmac is a bagged repair material that you can use straight from the bag, with no heating and no plant. It is good at what it is designed for: filling potholes, patching trenches and tidying small damaged areas on a driveway or path. It is not a way to surface a whole drive, and it will never match the strength or finish of the hot-laid tarmac used on properly built tarmac driveways.
What is cold lay tarmac?
Cold lay is a mix of aggregate and bitumen with a solvent or reactive binder added so it stays workable at air temperature. Hot tarmac arrives from the plant hot and hardens as it cools. Cold lay works the other way round: it goes down cold and firms up as it is compacted and as the solvent slowly leaves the mix.
There are two broad types. Solvent based products harden gradually over days and weeks as the solvent evaporates. Water activated or reactive products cure much faster once water is sprinkled over each compacted layer. Both come in fine 6mm grades for paths and light use and coarser 10mm grades for heavier traffic.
Is cold lay tarmac any good?
Yes, for small repairs, as long as you prepare the hole and compact it properly. A well rammed cold lay patch in a driveway pothole can last for years. The patches that fail are nearly always ones tipped in loose, laid in a wet or dirty hole, or left proud with no compaction, so they lift out under the first few tyre turns.
Where it falls short is anything structural or anything large. Cold lay has no binder course under it, it does not bond to the old surface the way hot material does, and it never fully matches the colour and texture around it. It also does nothing about the cause of the pothole. If water is getting under the drive or the sub-base has gone soft, a cold patch will be back to a hole within a season or two.
How to use cold lay tarmac
You need a stiff brush, a spade or trowel, a hand rammer (or a hired plate compactor for anything over a square metre) and enough material. One UK cost guide puts a 25kg bag at roughly 0.2-0.3m² of coverage, and a deep pothole uses it up fast. Buy more than you think.
Cut back to sound material. Remove loose stone and crumbling tarmac until the edges are firm. Square, vertical edges hold a patch far better than a feathered dish.
Clean and dry the hole. Brush out dust, leaves and standing water. A wet or dusty base is the most common reason patches fail.
Prime the edges if the product calls for it. A bitumen bond coat or jointing spray around the edges helps keep water out of the joint.
Fill in layers. Deep holes go in two or more layers, each one compacted before the next goes in. Trying to compact 80mm of loose material in one go leaves the bottom soft.
Overfill slightly and compact hard. Leave the last layer about 10mm proud, then ram or plate it down until it is level with the surrounding surface. Wet the rammer to stop the material sticking.
Seal the joint. Sealing round the edge of the patch slows water getting into the join between old and new.
Most bagged products can take light traffic straight away, but full hardening takes much longer, especially in cold or damp weather. Avoid turning car wheels on the patch while stationary for the first few weeks.
Can you lay a whole driveway in cold lay tarmac?
Technically you could spread it, but it is a false economy and nobody who lays drives for a living would do it. A properly built drive has a compacted sub-base of at least 100mm, a binder course of around 50mm and a surface course of around 20-25mm on top. Cold lay replaces only the top of that, has none of the structural strength of a hot binder course, and costs far more per square metre once you buy it in 25kg bags.
If the drive is broken up in more than a few places, the useful question is whether it can be resurfaced or needs digging out. A proper relay means digging out, building the base and laying hot tarmac in two layers, and our guide to tarmac driveway cost covers what a full relay typically costs compared with patching.
Hot lay vs cold lay: the practical differences
Strength: hot tarmac is compacted with a roller while hot and bonds into a dense, continuous layer. Cold lay relies on hand compaction and a slower cure.
Finish: a hot surface course gives a uniform black finish. Cold patches stay visible.
Bond: hot material laid against a cut and sealed edge forms a tight joint. Cold material sits in the hole and depends on compaction and sealing.
Who lays it: cold lay is a genuine DIY product. Hot tarmac needs a crew, a roller and a delivery timed to the job, and is not a weekend task.
Modern tarmac, hot or cold, is bound with bitumen rather than tar. Tar has not been used in asphalt production since the 1980s.
When is a cold patch the wrong answer?
Check these before you buy bags:
The patch area keeps growing. Several potholes in a line or a spreading area of crazing usually means water and a weak base, not a surface problem.
The surface is sinking. A dip or rut means the layers below have moved. Filling the dip with cold lay adds weight and hides the cause.
Edges are crumbling. Frayed edges usually mean there is no kerb or edging restraint. Pavingexpert is clear that free edges of a bitmac drive need edgings, and no patch fixes a missing edge.
Water ponds on the drive. If the falls are wrong, puddles will keep softening any patch you put in.
Cold lay tarmac questions, answered
Can you lay cold lay tarmac in the rain?
Standard solvent based products should not be laid in rain or into a wet hole, because water stops them bonding. Some products are designed for wet weather or are water activated, so read the bag. In cold weather the material stays workable but takes longer to harden.
Can you put cold lay tarmac over concrete?
You can patch a hole in a concrete drive with it, and it will stick if the concrete is clean, dry and primed. It will look like a black patch on a grey drive. For a pattern imprinted surface, a matching concrete repair or a reseal is usually the better route; our pattern imprinted concrete driveways page shows how those drives are built.
Does cold lay tarmac need sealing?
Not the patch itself, but sealing the joint round its edge helps keep water out. If the whole drive looks faded and grey, that is a different job, covered in our post on tarmac restorer.
When to call a contractor
Use cold lay for the odd pothole, a service trench or a damaged corner. If your drive has more patches than original surface, sinks in places or holds water, it is time for a proper look at the base. With over 25 years of Wolverhampton drives behind us, we are happy to tell you whether a patch, a resurface or a full relay makes sense. You can ask us for a free site visit.
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