Flexible Cabro Block Pavement
Construction of a flexible block pavement involves preparation and installation of the following layers. To all residential flexible block or brick paving installations, whether on a drive, patio or for a path the following is necessary to obtain a durable flexible pavement.
Sub Grade
The surface needs to be dug off to a depth of approx. 200mm removing any organic material. Ensure sub-grade does not have much clay or deep rooted weeds.
Kerbs
Kerbs must be laid on and haunched with concrete in order for it to restrain the body of the paving and prevent it from disappearing into the garden. Kerbs for flexible block pavements are normally laid on a concrete bed directly over the sub-grade layer or in a shallow channel excavated into the sub-base to ensure a full 100mm depth of bedding material. Bedding the kerbs over the un-altered sub-base results in too shallow a bed and haunch.
Sub Base:
The blocks are not mortared together, they are separated from each other by 3mm or 4mm of loose silica sand. The blocks are laid on a sand bed, there is no cement or concrete used in the bedding, except for the perimeter edges. How can such a construction carry the weight of cars, vans, etc?-The Sub-base
This is the load-bearing layer of a block pavement, and should never be omitted.
The sub-base should be a minimum 100mm thick, but in exceptional circumstances could be reduced to 75mm for paths or patios on good ground
Note that the completed paving will need a slope of not less than 1:80 to ensure adequate drainage of surface water.
The laying course material needs to be a consistent thickness so the slope must be established at this stage in the construction process, in the surface levels of the sub-base.
Edge Course
Following completion of the sub-base, the edging courses of the paving should be constructed before placing the bedding layer and the blocks. Blocks should be laid on a concrete bed and haunched to prevent lateral movement of the paving.
Laying Course
The paving blocks should be laid directly onto a bed of coarse, grit sand, 25-40mm thick. This sand may also be known as sharp sand, concreting sand.
Avoid using BUILDING SAND - it is too soft and when waterlogged, may move beneath the paving, causing settlement.
Paving Layer
The paving blocks should be laid to a specific pattern.
A fully interlocked pattern should be used for areas used by vehicles whenever possible or practical. Other patterns are fine for foot-traffic areas such as paths and patios.
The perimeter edge courses of the paving should have been laid after the sub-base, and should by now be set solid on their concrete bed and haunching.
Lay all the full blocks first, taking care not to stand on the levelled bedding layer, but working from the laid paving. Use a tight string line as a guide to the laying line if required and generally aim at a 3mm joint between blocks.
Compacting
Use a vibrating plate compactor to consolidate the blocks once they are laid.
The plate compactor vibrates the paving units, driving them downwards and settling them into the laying course.
Jointing is achieved by filling the 2-5mm close joints with specially selected jointing sand which then generates a phenomenal amount of frictional interlock between the adjacent blocks.
Dry jointing required can only be done in dry conditions using kiln-dried silica sand, designed for this purpose.
Simply brush the sealing sand over the surface repeatedly, allow to trickle down into the joints between the paving units. Once the joints are as full as possible, all of the excess sand should be swept off the paving, or into a corner where it can be salvaged for re-use.
The vibrating plate compactor should make a couple of passes over the paving, in different directions, to vibrate and settle the sealing sand, and complete any partial compaction of the paving units.
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