A sub-base is an important part of any tarmac surface. It provides strength, stability, and helps with drainage. MOT Type 1, an aggregate mixture, is the most commonly used material for the construction of a tarmac subbase. Concrete however can also act as a suitable base.
So, if you have an old concrete driveway that’s seen better days, you might be wondering: can you simply lay tarmac straight over it? The short answer is yes, but there are some factors to consider. In this article, we cover every you need to know about tarmacing over concrete.
Benefits of tarmacing directly over concrete
There are many benefits to tarmacing over an existing concrete surface. Removing the need to rip up the old slab can substantially reduce the project costs, both in labour and the disposal it comes with. The cost, however, isn’t the only advantage worth considering.
Strong, stable foundation
Concrete provides a solid and durable base for the tarmac layer, helping the finished surface better withstand heavy loads.
Reduced waste and environmental impact
Reusing existing materials results in less waste being sent to landfill and lowers the demand for new material.
Faster installation
With the sub-base already in place, the preparation stage is shorter. This means the tarmac surface can often be installed and completed more quickly.
When not to lay tarmac over concrete
Old concrete can make a suitable sub-base, but it needs to be in reasonable condition. If the surface shows major cracks or significant deterioration, removal should be considered instead.
A sub-base helps the tarmac surface maintain its structural integrity over time. Laying tarmac over concrete that’s visibly past its best is almost guaranteed to result in premature surface failure.
Minor cracks and damage may be repairable, and the surface may still be suitable. More significant damage is likely to compromise structural strength, shortening the tarmac’s lifespan and increasing the need for repairs. Signs that tarmac shouldn’t be laid over concrete include:
- Major cracking
- Uneven with sunken sections
- Deep pothole
- Fretting and crumbling
Best base types for tarmac
MOT Type 1 and Type 3 are the best sub-bases to lay tarmac over. Concrete, however, is completely suitable too, with all three offering great load-bearing capacity and stability. MOT Type 1 is an aggregate mixture and the standard choice for driveways, offering a strong, well-compacted base. MOT Type 3 is also an aggregate mixture, but with reduced fines, allowing for greater drainage.
Both Type 1 and Type 3 are excellent sub-base materials but serve different purposes. Installing either from scratch means excavating the ground and laying the aggregate, which can cost thousands of pounds. Removing old concrete alone typically costs around £22 to £35 per square metre. Should it be in good condition, laying tarmac over it instead can save both this removal cost and the expense of installing a new sub-base from scratch.
Tarmacing over concrete – should you do it?
Laying tarmac directly over concrete is well worth considering. A concrete sub-base can offer the same quality as one laid on a traditional sub-base. The concrete however should be in structurally sound condition. Any damage in the concrete will quickly be reflected in the finished surface above.
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If you’ve got a question about tarmac or need expert advice, contact A&MT today. With over 50 years’ experience, we’re a team of professional surfacing contractors, highly experienced in tarmacing. From replacing your concrete driveway to the reinstatement of potholes, we’ve got you covered.
For a free, no-obligation quote and site visit, get in touch with our team of experts. Whatever you need, wherever you are, no project is too big or small for us. We’re proud to complete work throughout Cambridgeshire, including Peterborough, Cambridge, Huntingdon, Wisbech, Ramsey, and March – as well as the surrounding counties.
