Tarmacadam
Whilst not strictly ‘paving’, there may be times when a landscaper may be called upon to
lay a small area of tarmac. Large areas call for specialised equipment, including heavy duty
vibrating rollers and heated vats in which to prepare the bitumastic sealants and soften the
tarmac material.
By way of introducing tarmac to non-tarmac professionals, it should be known that they are
similar methods of preparation for carrying out the works as those used for paving projects,
including the requirement to reduce dig to a depth suitable to bear the weight of the likely
traffic, especially in driveways and car parks, where oil delivery lorries and dustcarts may
stand, with their engines running. The resultant vibrations may cause settlement in the
subbase under the tarmac veneer.
The ground should be excavated to a depth of not less than 300mm, with suitable sub-base
including MOT Type 1 laid over a geotextile membrane. The tarmac is laid in two distinct
layers known as the base and wearing coats. The base is usually 10mm stone covered with
bitumen and the wearing coat 5mm. Both may be permeable if laid over a permeable sub-base.
(Tarmac may be laid over concrete on some projects requiring a more substantial base, and a
layer or coating of hot laid bitumen should be applied to the whole of the concrete surface)
It should be laid in one ‘sheet’, having regard to the weather conditions. If it is frosty or
raining, it should be deferred until the temperatures have risen and the ground dried out. If laid
over frozen ground, the asphalt will also freeze and become hard, which may cause cracking
once the temperatures rise.
If it is not possible to lay the whole area in one operation, due to loading and availability from
the supplier, the old work should be sawn to a clean line in preparation for the next tranche.
This cut line will require a coat of liquid bitumen to seal and adhere to the new load and
prevent cracking between the separate plates.
If using bags of ‘cold-lay’ tarmac, sometimes required for small areas of patching or creating
ramps between levels of paving and driveways e.g. against public footpaths at entrances, be
aware that you will need heat to make the product malleable. Too often, it is akin to laying a
solid block, rather than a patching product. Practical only on very warm days, or warmed up
by other means, it will require a metal tamp to firm it into position.
