Laying a tarmac driveway begins with a site assessment. Once measurements have been taken and the required calculations have been made, excavation can begin. Finally a subbase is laid and the tarmac can be installed.
In this Guide:
Planning and Preparation
1. Site Assessment
Before starting work, the site should be assessed for possible drainage issues to ensure water does not pool on top or cause any flooding issues.
Local Regulations should also be considered to ensure you are not in breach of any planning permissions by installing the driveway.
The fall of the driveway should be determined at this stage, and a fall of 1:60 is recommended to allow for surface water runoff.
2. Initial Calculations
The driveway should be measured to determine the amount of tarmac required to cover the area.
A Tarmac driveway will generally be laid in the following 3 steps:
Subbase
Binder Course
Surface Course
The following calculation should then be used to get the amount of tarmac required in m3 as this is the unit your supplier will require when purchasing.
Length x Width x Depth = Tarmac Required in m3
Example:
If a driveway is 10m wide and 15m long and we choose to use the following specification for the job.
Here is our Specification:
Subbase - 150mm
Binder Course - 50mm
Surface Course - 30mm Here are our Calculations:
Subbase - 10m x 15m x 0.15m
Binder Course - 10m x 15m x 0.05
Surface Course - 10m x 15m x 0.03
Here are our required Materials
Subbase - 22.5 m3
Binder Course - 7.5 m3
Surface Course - 4.5 m3
3. Tools Required
A few tools will be needed to install the Tarmac driveway depending on what type of machinery you choose to use.
Tools required to lay a tarmac driveway:
Shovel
Rake
Tamper
Wheelbarrow
Compactor / Roller
Excavator / Spade
Excavation
Any existing material should be removed from site. An excavator can be hired to carry out this task as it is very labour intensive without. A 1.5 tonne excavator is the ideal size for most residential projects.
Excavator Cost
A 1.5 tonne excavator will cost roughly £140 per day on hire and an additional £150 delivery cost.
A 3 tonne excavator will cost roughly £210 per day on hire and an additional £150 delivery cost.
Please Note: When hiring an excavator for a full week, costs per day are significantly reduced.
The material excavated should be moved to another location on the property or taken off site.
Lay the Sub-base
To install the subbase spread the stone evenly across the excavated area and use a compactor to compact the material. The subbase should be level and evenly compacted, 2 rounds of compaction will ensure the stone is stable.
What depth subbase for a tarmac driveway?
A depth of 150mm mot type 1 stone is recommended to provide a stable foundation for a tarmac driveway on a residential property.
Install the Edging
Once the subbase has been installed the edging can be secured. This will provide well defined edges for your driveway and help to keep the tarmac even when compacting. Edging tarmac also helps to preserve the tarmac by stopping water from seeping into the sides and causing freeze thaw degradation.
Some common materials that can be used as edging include:
Kerbs
Bricks
Blocks
Cut Stone
How should the edging be secured?
The edging should be secured using a mortar or concrete mix, this will ensure the edging stays in place over a long period of time.
Install the Tarmac
Firstly a binder course will be installed which will require compaction to level. This is followed by the surface course which contains smoother aggregates and will result in a finer finish to the driveway
1. Installing the Binder Course
The binder course is made up from coarse aggregates and bitumen which provides a solid foundation for the surface course and will form a stronger bind to the subbase than a surface course with finer aggregates.
The binder course will need to be levelled and compacted to roughly 50mm deep; to clarify, this should be a 50mm depth after compaction.
A roller is recommended when compacting the binder coarse as it will allow for easier levelling than a compactor/whacker plate.
2. Installing the Surface Course
The surface course is then laid on top of the binder course and raked to ensure its level before compaction.
A 30mm depth will be adequate to level the tarmac and allow enough movement to achieve a smooth finish without bumps.
A roller is recommended for compaction of the surface coarse as this will make sure the tarmac is compacted fully but also allow the tarmac to move which will make it easier to keep a level surface free from slopes.
A fall of 1:60 is preferred to ensure surface water is able to runoff the driveway and avoid pooling. This means for every 60cm across the surface there should be a 1cm fall in height.
Finishing Touches
Once the tarmac has been laid allow up to 48 hours for the driveway to set. Avoid using the driveway during this time to give the tarmac time to fully cure and harden.
Please note: If you live in an area with a warm climate you may need to allow for an additional 24 hours for the tarmac to set.
Edging may need to be reinstated if the ground was disturbed during installation, although this may just be a matter of a few bags of soil and grass seed to tidy up the edges. Alternatively a decorative gravel could be used but this is dependant on what ties in best to the outside edges of the driveway.
Sources: