Block Paving Installation Guide
Header Photo Credit – Taylormade Landscapes
First and foremost when starting or quoting for any driveway, SuDs specification should be taken into account. With local planning authorities now handing out large fines to contractors for constructing non-compliant driveways, this is an imperative.
Levels Assessment
Next consideration is the finished surface course levels which are often governed by three key levels; garage floor, public footpath levels and the damp proof course (DPC) on the house. The block paved surface course should finish 150mm below DPC.
It’s worth pointing out at this stage that some driveways and car parking areas are level or have little fall, which may only leave the option of permeable paving or a channelled drainage system, dishing into individual gulleys and drains.
Due Diligence
Next step is to locate gas pipes and CAT scan to detect any electric cables or gas pipes, investigating by hand excavation as necessary.
Marking Out & Excavation
Mark out site and double check measurements. A good contractor will always design a project to avoid small cuts of less than 1/3 of the unit size if possible.
Excavate to firm ground which would be a minimum depth of 230mm assuming 50mm deep blocks are being used as the surface course to allow for the base, laying course and block. Noting poor sub-grades may require a sub-base or a capping layer or improvement layer.
Once you have excavated to formation level, ensure your sub-grade is graded to the same fall as your surface course which should be a minimum 1-80 longitudinal fall and if levels are acceptable, a cross fall of 1-100. Variation in base and laying course depths may lead to uneven compaction, which in turn may increase the chance of failure.
At this stage it would be good practice to employ the foot test as described in British Standard BS7533:102 which would give you an indication of the Californian Bearing Rating (CBR) which you can then relate to BS7533:101 and design your sub-base/base accordingly. It is always better to remove another grab wagon off-site and bring another load of type 1 in or 6f2, than have to relay the whole project 6 months down the line due to base failure.
Any soft spots or ‘cows belly’ as we call it up North should be dug deeper and filled with lean mix or compacted type 1.
Compact the subgrade. If the weather is inclement, remove saturated spoil and install a layer of 6F2 and compact. It is bad practice to install a base on a saturated subgrade.
Base & Sub-base Construction
At this stage, install a geotextile separation membrane. If the sub-grade is weak or heavy clay in particular a Marl clay, then I would highly recommend installing a geogrid to help with stability and to distribute the load.
Upon delivery of your MOT type 1, a close inspection should be carried out to its moisture content. It should be moist but not saturated. If it is too dry, it will not be lubricated sufficiently and will lack interlocking capacity. Too wet, it can lose its load-bearing capacity.
Next, install the edge restraints either on a concrete race or edge beam at a minimum of 100mm base depth. The edge restraints should feature a vertical face extending down to the underside level of the laying course and need to be haunched in concrete at the base and rear to reduce lateral movement at a minimum of 50% of the vertical face. Laying and haunching as you go ensures a stronger, monolithic unit. Adding haunching at a later date creates a weak bond and is bad practise.
Lay MOT type 1- assuming non permeable surface courses – and compact in layers using a ride on double barrelled vibrating roller or a walk behind forward and reverse diesel heavy-duty whacker plate with a minimum of 5 passes longitudinal and horizontal.
For driveways steeper than 1 in 20, intermediate edge restraints should be installed.
Screeding
By using sharp sand when the first compaction of the laying course is completed, the sand will partially travel up the bottom of the joint which provides superior interlocking capacity. The sand should be moist but not saturated as this will aid compaction. You will be aiming for a final compacted depth of 30mm throughout.
Screed rails should be used on large areas. When removing the screed rails, fill the voids with sharp sand and compact with a float. I recommend leaving these areas slightly higher by a couple of millimetres. The block pavers should be left 3-5mm higher than the edge restraints, ready for final compaction.
The laying course should be of a smooth, even gradient. To achieve this, there are several techniques. However, my preferred way was to compact a layer of sharp sand with one pass with a compaction plate at approximately 40mm depth, re screed to 33mm and then lay the block pavers.
If you prefer, distribute the laying course material in a single layer and compact it using a whacker plate. Scratch out the top 10mm with a landscaper’s rake prior to laying the blocks. Alternatively, screed out 25mm of the laying course material, compact it, and then screed out an additional 10mm of loose material before starting the laying process.
Pattern Selection
Both 90-degree and 45-degree herringbone patterns are by far the strongest Interlocking of all the patterns.
Stretcher bonds, random and half stretcher bonds are also a choices. Basket weave and ‘squared’ laying patterns are not recommended for driveways as they are prone to translocation when under pressure from turning wheels.
Laying The Block Pavers
Contrary to popular belief the ‘nibs’ on the sides of block pavers are not joint spacers as such, but are actually to protect block pavers from damage whilst in transit. Block pavers should be loosely packed together not too tightly, to give a minimum 2mm gap – 5mm being the maximum joint width.
With the above information in mind setting up string lines both perpendicular and horizontal are essentials, so as to not wander out of square and keep the perpendiculars in line. Distances over 6m line require ‘tingles’ or intermediate pins to be used to prevent line sag. The horizontal lines should be set a couple of mm off the block so the line isn’t fouled, remembering the unit will be installed appropriately 3mm higher than the edge restraints. The horizontal string lines will require moving to new locations every metre or so, with adjustments made if necessary and make sure you remain parallel to your start point or base line.
Begin laying against the edge restraints or base line working up the gradient. Before laying check the batch codes match, with cheaper blocks nonmatching codes the colour shading differences can almost be night/day. Blocks should be taken from a minimum 3 packs to avoid the patchwork quilt effect. Rather than removing blocks from rows take them out of the packs vertically and diagonally at 45 degrees.
When cutting blocks use a cut off saw, table saw or block splitter. No blocks should be less than a 1/3 of their unit size. Inboard cuts are a good practice to use especially at the entrance to driveways as smaller pieces may become dislodged.
Where possible, place the cut face of a block against an adjacent block chamfer instead of an edge restraint – not forgetting to install loosely and not butt joint.
Many sands have a high iron and clay content, so it is important to keep them off the surface of the blocks, especially open textured block, as staining may be difficult to remove.
Compaction
Compact the paving using a vibrating plate compactor with a geosynthetic protection matt fitted to the base.
Lay block pavers with a chamfered or tumbled edges and compact the surface without joint kiln dried sand initially.
For pencil edged blocks, spread joint filling sand over the surface before compaction to protect the edges of blocks and to stop them coming into contact with each other.
Inspect the completed paved surface, and remove or remediate any cracked or chipped blocks.
In inclement weather, especially in winter when the surface of the block pavers rarely dries out, the washing in technique of kiln dried jointing sand may be employed, but it is important not to saturate the laying course or this may cause the sand to become liquified. Therefore, the laying course material should be free draining with minimal fines. ‘Wet sanding’ is also a good way to reduce silica dust inhalation.
Cover the surface with kiln-dried joint filling sand and carry out a second compact pion.
Tolerances – The surface tolerances are 10mm under a 3 metre straight edge.
Finishing
Brush excess kiln dried sand off the surface of the blocks.
Joint stabilising products are available to hold the kiln dried sand in place and prevent migration into the laying course.
To meet BS7533:102 adjacent blocks should not differ in level by more than 2mm to avoid trip hazards. Conduct out a visual assessment of the surface course. Surface depressions of the blocks, should not exceed 10mm when measured with a 3m straight edge to avoid depressions and ponding.
Maintenance
Maintaining a block paving driveway in the UK involves regular care and attention to ensure its longevity and appearance. Here are the key factors: 1. Regular Cleaning Keeping the block-paved surface clean with regular brushing to remove debris will prevent the buildup of organic matter and protect it from staining and algal growth.
Occasional light pressure washing to remove algae dirt is recommended; avoid heavy pressure washing. Power washing will remove jointing sand and may therefore, require topping up. Weed and moss killers may be applied regularly to prevent their growth and spread. Sealants may be applied and reapplied every few years or as per the manufacturer’s specifications. They are a good defence against moss, algae, oil, and diesel stains. Channel drains require regular maintenance, as do any surface defects or degradation. A reserve of block pavers should damage occur, or persistent oil stains become a problem is recommended. In areas with low areas and water pools upon the surface, hire a professional to lift and relay that area as soon as possible. Pooling water may create a slip hazard and rapidly deteriorate the surface with freeze-thaw cycles and encourage algal growth. Avoid using rock salts as these can degrade the surface.
Gareth Wilson – Paving Site
