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Block Paving Installation Process
Here we will cover the various stages of concrete block paving installation, including: –
1. Block Paving Installation – Design
Once you have chosen the particular block paver you wish to have installed on your driveway or patio area, you can use the manufacturer’s software to create a laying pattern if you have not prepared one of your own.
Considerations to be taken into account include the colour of the block (it should contrast with, rather than clash with the brickwork on your home) and whether the driveway is being extended or widened from its existing size and shape.
Changing the surface of an existing driveway provides an excellent opportunity to start again with a blank sheet of paper, dealing with questions such as: –
- Do you need an additional car parking space in your block paving installation?
- Would you prefer a curved driveway rather the straight one that the original house builder may have installed?
- Is a separate footpath required leading to the front door, or for side access?
- Would you like any features building in to your p block paving installation such as planting areas to be included?
A typical block paving layout plan for a driveway could appear like this one, showing a 90º herringbone pattern and a border block: –
The final design for the driveway or patio area should incorporate any kerbs or edging restraints between the driveway and the garden, surface and underground drainage (including disguising unattractive man hole covers) and steps up to raised areas or to provide access to the front door. Get your block paving installation and design right and you will grossly improve the kerb appeal of your home.
2. Block Paving Installation – Excavation
The first job in a block paving installation is to mark out the area which needs to be excavated, either with pegs and a string line or with a proprietary groundwork line marker spray paint which can be used on grass, tarmacadam, paving slabs or soil.
Prior to any excavation though, you should be aware of the position of all existing underground services including drainage, gas and water pipes, and any cables such as telephone and cable television. Any damage caused to these services will not only add to the expense of the project but will also delay your block paving installation.
The size of the block paving installation will dictate whether a mini-digger should be used as digging by hand will be back breaking work and take much longer. The area should be excavated to the required depth, allowing for the sub-base, sand and block thicknesses, whilst ensuring that the finished surface level is still 150 mm below the damp proof membrane of the property. This is to satisfy Building Regulations and reduce the effect of rainwater splashing above the damp proof course during a heavy downpour, which could eventually lead to a damp problem inside the house. The slope of most driveways will dictate the position of any drainage but if the area is relatively flat then a fall needs to be created to allow surface water to drain away effectively, leaving no puddles. This slope should be approximately 1 in 40 across the width of the drive and 1 in 80 along the length to be effective on an otherwise flat area.
3. Block Paving Installation – Edge or Kerb Restraints
In most cases, kerbs or edge restraints are vital in any block paving installation, between a newly block paved surface and any soft landscaping such as a border or a lawn to hold the blocks of a driveway within a firm border, like a frame to a picture, giving the surface area integrity.
A string line should be positioned to determine the line of the edge restraints and to set them at the correct height, using a spirit level. The edging blocks should be concreted into position with 1 part cement to 6 parts ballast (a mix of gravel and sharp sand), to create a 100 mm deep foundation. This will hold the blocks in firmly to provide strength and longevity. The kerb blocks are now mortared into place using a trowel and tapped into their final position with a rubber mallet. Once in the correct position, you should haunch the back of the edge restraint blocks – this involves laying mortar at a 45º angle half way up the back of the kerb, that is, the side facing the soft landscaping.
4. Block Paving Installation – Surface Drainage
Once the site has been excavated but before any sub-base material is added, all the surface and underground drainage supplies need to be installed. These can consist of open gullies, linear drainage (aco drains) and soak-aways or underground rainwater harvesting systems.
If any steps are to be constructed, now is the time to prepare the concrete pad which will support them, so that it has time to harden prior to building the steps. The concrete foundation and the mortar holding the edge restraints and surface drainage in position should also be allowed to harden, or cure before the sub-base for the block paving is installed.
5. Block Paving Installation – Sub-base Material
As with most home improvement projects, and certainly with a block paving installation, preparation is one of the most important factors in the project. Whether you are sanding down an internal door prior to painting it or laying a sub-base for a driveway, appropriate preparation is vital. A badly laid sub-base with insufficient material or which has been poorly compacted will inevitably lead to sunken areas on the driveway. The only solution for which is to remove the blocks, install a good quality sub-base and re-lay the blocks – it may as well be done correctly in the first place.
Before the sub-base is installed and compacted, there is an option to lay a geo-textile membrane. Some contractors may refer to it as a weed membrane but there are doubts as to its usefulness for that purpose on a well-constructed driveway. Unless there is a known threat from particularly pernicious weeds such as Japanese Knotweed or Horse Tail. The main purpose of a membrane in a block paving installation is to prevent particle migration of the Type 1 MOT hard core down into the subsoil where it can potentially be washed away. This could lead to sunken areas within your new block paved driveway or patio.
String lines should be set to identify the levels you are working to. MOT Type 1 roadstone, or hard core, can then be laid inside the edge restraints, raked level and compacted with a vibrating plate. The hard core should be at least 100 mm thick after compaction but should be laid in 50 mm deep layers. Approximately 70 mm to 75 mm of hard core should be installed first as this will compact down to around 50 mm, though it will take 6 or 7 passes with the vibrating plate to achieve this. This process should be repeated so that there is a total of at least 100 mm compacted hard core. By doing it in this way you will ensure proper compaction at the lower levels of the sub-base. Installing 150 mm of hard core and then compacting it, will result in the lower levels of the sub-base remaining loose, this will eventually settle and cause undulations in the finished block paved surface.
6. Block Paving Installation – Screed
Once the sub-base has been installed and the levels have been checked, a 30 mm to 50 mm deep layer of slightly damp sharp sand should be laid, raked and compacted. If the sand is too dry it will not compact effectively and will remain loose. A good guide is to try to form a ball of sand in your hand – if the ‘ball’ collapses and the sand falls apart once you open your clenched fist, it is too dry.
A second layer of sharp sand approximately 20 mm thick is then applied on top of the compacted layer. With string lines, a straight edge and screeding rails, this second layer of sand should be levelled to create the desired falls. A screeding rail can be a straight length of copper pipe which is temporarily embedded in the second layer of sand to be used as a guide for the straight edge. Once this is moved, the gap should be back-filled with sand and the screeding rail is moved to its next position.
7. Block Paving Installation – Laying the Blocks
For almost all block paving installations on driveways and patio areas you will require more than one pack of blocks, which are normally delivered to the site on wooden pallets. Before accepting delivery of the blocks you should try to ensure that they are all from the same manufacturing batch, just as you would with batches of wall paper or paint. Slight colour differences can occur between batches which are manufactured at different times, due to the mixture of concrete, pigments and even the amount of moisture in the atmosphere at the time of production.
When laying blocks, even if they are all from the same manufacturing batch, you should use blocks from at least 2 or 3 different pallets at the same time to minimise any slight differences in colour across the newly paved surface. Failure to do this, especially when laying blocks with a multi-blend of colours, can result in a concentration of particular colours in certain areas of the driveway or patio which will give a patchwork quilt look.
Positioning the blocks – You should always start laying blocks from the bottom of a slope (start at the top and they could slip down during the laying process), and preferably starting from a straight edge or a perfect right angle. When laying one block against others, you should hold it directly above its proposed position and then place it down vertically, rather than with the leading edge first, otherwise you will cause an indent in the top layer of sand and the block will not sit level. Because the top layer of sand was screeded and not compacted, blocks will sit approximately 4 to 5 mm above the required finished level initially, allowing them to be compacted later.
Border blocks – Most block paved driveway and patio areas look better with a block border of a contrasting colour (or even a different size and texture) from the main blocks, fitted in a line inside the edge restraint blocks. The easiest way to do this is once you have installed all of the full blocks, position a border block inside the edge restraint over the main blocks and mark it’s inside position on the main blocks. These can be removed from the driveway, cut along the scribed mark and replaced leaving exactly the space you need to insert your border block.
When all of the full blocks are in position in your desired pattern, you will need to cut others to fill the smaller gaps. Paving blocks are cut with a block splitter or a diamond disc stone saw, though the latter will generally give a better cut than the former. Water should be used with a stone saw to reduce the dust but whichever method you employ, health and safety is critical at this potentially dangerous part of the process. As a general rule you should try to avoid using small sections of block as infill pieces which are less than a third of the original block size as these are less likely to sit level, on the sand below.
8. Block Paving Installation – Finishing Touches
When your block paving installation is completed and all infill sections of cut blocks are in position and border blocks are in place, any debris on the surface should be cleared away and the blocks swept clean.
Kiln dried sand, sometimes referred to as silica sand, is then spread over the surface, swept into the joints between the blocks and compacted with a vibrating plate. More sand is applied, swept and compacted again to lock all the blocks together. This process should be repeated until all the joints are full of sand and the block paving surface is properly compacted. Any excess sand can then be removed from the surface.