How to install Clay Pavers. Clay pavers are timeless classics that look equally good on old and new properties, thanks to the wide variety of colours, surface finishes and textures. Due to their low water absorption and density, clay pavers weather well and last a long time when installed correctly.
Design and Installation Factors and Considerations
T1 to T4 clay pavers are acceptable for a patio, noting T4 is overkill for a patio and likely to be an unnecessary greater expense.
T-rating under BS EN 1344 classifies a clay paver according to its transverse breaking load, which is the measured force (in Newtons) required to fracture the unit in a controlled bending test. It is not the same as flexural strength expressed in MPa, although flexural stress can be calculated from the breaking load and the unit’s dimensions. The classes range from T0 to T4, with T4 being the highest standard category. In practical terms, the T-rating indicates the paver’s resistance to cracking under bending forces such as vehicle wheel loads, with T3 generally suitable for residential driveways and T4 offering a greater margin for heavier or more frequent vehicular use.
Consider the laying pattern to be used, such as stack bond, half bond, 1/3 offset bond, or herringbone. These are the strongest bonds and are especially good on driveways. Set out the area so that minor cuts of less than 1/3 are avoided at the edges of the paved areas: this is important not only for aesthetic reasons but also for the structural integrity of the paving. Inboard cuts should be installed to avoid cuts less than 1/3.
When installing clay pavers, a minimum fall of 1:60 should be provided for each subgrade, the MOT type 1 base, the laying course, and the surface course. British Standard BS7533:102 recommends 1-60 fall; however, 1-80 is accepted as the minimum. The British Standard BS7533:102 specifies a tolerance of 2 mm for level variation between adjacent paving units.
Drainage must also be considered, especially where paving meets a lawn. If there is no drainage at the bottom of the end fall, it can often cause a wet, boggy lawn. Drainage should be installed every 10m of fall for large paved areas.
Check Points
Upon delivery of your clay pavers, it is vital to check that all the batch codes match on the crates of paving. If the batch codes do not all match, contact suppliers and change the crates for all matching batch codes. Clay pavers are fired in large kilns, and there are often visual variations between batches. Differing batch codes are a warning sign that the pavers may vary notably in shade and/or pattern, creating an unintended, undesirable colour banding effect.
Before installation, ensure the finished level of the paving is 150mm below the damp-proof course of the house and, preferably, falls away from the building. Should there be no option to fall the paving away from the house, the best practice would be to have the first 300mm to 500mm of paving fall away from the building, then install a channel drain, and have the rest of the paving fall towards the channel drain.
Excavation
The minimum excavation depth is 200mm to accommodate a 100mm compacted depth of MOT type 1, a 40mm bedding mortar/laying course, and 60mm for the clay paver.
If you are unsure about the strength of the subgrade, conduct the boot test as outlined in British Standard BS7533:102, assess the subgrade as per British Standard BS7533:102, and adjust the excavation depths and foundation depths/layers accordingly to meet British Standard BS7533:101.
Subgrades with a CBR below 5% should increase the base depth to 150mm; below 2% layers on a reinforced concrete slab, or consult BS7533:101 or seek professional advice.
All subgrade assessment records must be saved and filed.
The fall of the formation level should match that of the surface course and the foundation layers that follow.
Base – Sub-base Installation
When installing your base, it is best practice to lay a geosynthetic nonwoven membrane over the computed subgrade to prevent fine particle migration into the subgrade. The geosynthetic membrane should overlap by a minimum of 300mm.
Best practice, especially on poor subgrades, is to install geogrid/biaxial mesh. This is specifically designed for base stabilisation and reinforcement. Again, the geogrid should be overlapped by a minimum of 300mm, and suitable zip ties can be installed to connect them together, but shouldn’t be relied upon.
Edge restraints should have a vertical face below the laying course.
Install edge restraints into a 75mm -100mm moist concrete race/bed and haunch to a minimum of 50% to their rear. Apply haunching as you go to create a monolithic installation. Do not install the haunch after the concrete has begun to cure.
It is essential to allow the concrete to sufficiently harden before installing and compacting the MOT type 1 base.
Upon delivery of your MOT type 1, a close inspection should be carried out of 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. If it is too wet, it can lose its load-bearing capacity.
Next, install MOT type 1 to a minimum and consistent compacted depth of 100mm and at the same fall as the subgrade. The MOT type 1 should be installed in layers no more than 70mm deep, which will compact to approximately 50mm depth. Compaction should consist of 5 passes, both horizontally and perpendicular. A good indication that sufficient compaction has been achieved is the absence of lines in MOT type 1.
It is good practice to ‘dip’ the base, which is a method of installing two parallel string lines. Usually, the first string line would be 150mm below the damp proof course, and the second, running horizontally parallel to the bottom of the patio, 150mm from the subgrade. The string line is pulled taught every 1m to ensure an even distribution of MOT type 1, with no humps or hollows. Should there be low spots, they can be filled with MOT type 1 and compacted; high spots may be raked to low spots or levelled.
Laying Clay Pavers
Set out string lines to levels and falls, both horizontally and perpendicular.
The string line should not touch the edge of the pavers’ surface and should be 1-2mm away to ensure it is not displaced.
Before laying mortar, organic matter, such as leaves, should not be present on the type 1 base.
Set out your baseline string line, ensuring it is parallel to the house.
Perpendicular string lines should be installed 90 degrees to the baseline and no more than a metre apart. Horizontal string lines should be installed every 1m parallel to the baseline. This is to keep the joints even and in line.
For distances over 6m, line tingles or intermediate pins should be used to prevent line sag. The horizontal lines should be set a couple of mm off the aris so the line isn’t fouled. The horizontal string lines will require moving every metre, adjustments made if necessary, and making sure you remain parallel to your start point or baseline.
Start laying against the edge restraints or baseline, working up the gradient.
Before laying, check that the batch codes match to avoid colour banding. Even if batch codes match, clay pavers should be taken from at least three packs to avoid colour banding. Rather than removing blocks from individual layers, take them out of the packs vertically and diagonally at 45 degrees.
Mortar beds should be 1 part OPC, to 4 parts crushed rock 2/6mm as the preferred option, or 1/4mm, 2/8mm, or G85/20, properties of which should follow table C4 in BS7533:102.
Each clay paver should have a BS7533-certified bonding mortar applied to a minimum 95% coverage at a thickness of 1-2mm.
Clay pavers laid bound are generally hand-gapped at 5-6mm, DO NOT BUTT JOINT. Therefore, multiple perpendicular and horizontal string lines are required to ensure the chosen pattern remains perpendicular to the baseline, and horizontal string lines ensure the pattern remains parallel to the baseline. Due to the ±5 mm dimensional tolerances, spacers should not be relied upon solely.
When cutting blocks, use a cut-off saw, table saw, or block splitter. No blocks should be less than 1/3 of their size. Inboard cuts are a good practice, especially at the entrance to driveways. Cuts smaller than 1/3 can affect the structural integrity of the driveway.
If the clay pavers have a tumbled or chipped edge, it is good practice to dress and distress the cut aris. The cut aris can be rounded off using another clay paver and distressed/chipped slightly with a brick hammer.
Where possible, place the cut face of a block against an adjacent block chamfer instead of an edge restraint.
Clean the surface of clay pavers as you go to remove stains. Further mortar or bonding mortars stains should removed immediately.
Surface flatness of the blocks, should not exceed 10mm when measured with a 3m straight edge.
To meet BS7533:102 adjacent blocks should not exceed a 2mm tolerance.
Jointing
Check the weather forecast. If rain is imminent, then delay if necessary.
Clean the surface of the paving to ensure there is no contamination. A leaf blower is handy here.
Carry out a visual assessment of the surface course.
A BS7533 certified slurry grout is the preferred jointing material.
Aftercare
Regular maintenance is key, not only to the aesthetics but also to the longevity of the patio. Light power washing and proprietary cleaners are recommended.
Any deterioration should be attended to as soon as possible.
Clay pavers may be sealed with a breathable impregnator, but it is not a necessity.
