Header Image – Credits to Mark Loft Stockholm
Clay Pavers Installation Unbound Patio
Clay pavers are timeless classics that look equally good on old and new properties, mainly because there are so many different varieties of colour and texture. Due to their low water absorption and density, clay pavers weather well and last a long time, provided they are installed correctly.
Design and Installation Factors and Considerations
Consider the laying pattern to be used, such as stack bond, half bond, 1/3 offset bond, or the herringbone patterns. These are the strongest bonds and are especially good on driveways. Set out the area so as not to have minor cuts of less than 1/3 at the edge of the paved areas: this is important not only for aesthetic reasons but also for the structural integrity of the paving.
When installing clay pavers, a minimum fall of 1-60 should be installed to each subgrade, the MOT type 1 base, the laying course and the surface course. British Standard BS7533:102 recommends a fall of 1-60 as a minimum. The British Standard BS7533:102 tolerance for level variation between two paving units is 2mm.
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 differ notably in shade and/or pattern, creating an unintended and undesirable patchwork quilt effect.
Prior to 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 of falling the paving away from the house, the best practice would be that the first 300mm of paving falls away from the building, then a channel drain should be installed, and the rest of the paving falls towards the channel drain (see figure).
Excavation
The minimum excavation depth is 190mm to accommodate 100mm compacted depth of MOT type 1, 30mm sharp sand laying course and 60mm for the clay paver.
If you are unsure about the strength of the subgrade, conduct the heel test as outlined in British Standard BS7533:102 and adjust the excavation depths accordingly to meet British Standard BS7533:101.
The fall of the formation level should march that of the surface course.
Compact the subgrade.
Base – Sub-base Installation
When installing your base, it is best practice to lay a geosynthetic, non-woven membrane to prevent fine particle migration into the subgrade. The geosynthetic membrane should overlap by a minimum of 300mm.
A good practice, especially on poor subgrades, is to install geogrid/biaxial mesh. This is specifically designed for base stabilisation and reinforcement. Again geogrid should be overlapped by a minimum of 300mm and suitable zip ties installed to connect them together.
Install edge restraints on a concrete race/bed and haunch to a minimum of 50% up the side of the edge restraint. If you lay clay pavers as your edge restraint, apply bonding mortar to their underside. It is essential to allow the concrete to sufficiently harden before installing a type 1 base.
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. 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 that there will be no 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 at the bottom of the patio 150mm from the subgradel. The string line is pulled taught every 1m to ensure there is 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 Course Installation
Install sharp sand as per BS7533:101 specifications.
The thickness of the sharp sand laying course should be 30mm.
Screeding
When the first compaction of the laying course is completed using sharp sand or grit sand, as recommended in BS7533:101, the sand will partially travel up the joint, which provides superior interlocking capacity to grano or similar aggregates. The sand should be moist but not saturated, as this will aid compaction. You will aim for a final compacted depth of 30mm throughout.
Screed rails should be used in large areas. When removing screed rails, fill the voids with sharp sand and compact them 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 the final compactions.
The laying course should have a smooth, even gradient. There are several techniques for achieving this; however, my method was to compact a layer of sharp sand with one pass at 40mm depth, reseed to 33mm, and lay block pavers.
Or
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.
Or
Screed out 25mm of the laying course material, compact it, and then screed out an additional 10mm of loose material.
Laying Clay Pavers
Set out string lines to levels and falls.
The string line should not touch the edge of the pavers’ surface and should be 1-2mm away to ensure it is not displaced. String lines should have a tingle or intermediate line pin every 6m to prevent line sag.
Prior to 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.
Clay pavers are generally hand-gapped. Therefore, multiple perpendicular and horizontal string lines are required to ensure the chosen pattern remains perpendicularly straight, and horizontal string lines ensure the pattern remains parallel to the baseline.
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.
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, remembering the block will be installed appropriately 3mm higher than edge restraints. 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. With cheaper blocks that don’t match the codes, the colour shading can be almost night-day differences. Blocks should be taken from at least three 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 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, not forgetting to install loosely and not butt joint.
Many sands have a high iron and clay content, so it is essential to keep them off the surface of the blocks, especially open textured blocks, as staining may be difficult to remove.
Final Compaction And 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 rake is handy here.
Compaction should be carried out with a geosynthetic matt attached to the bottom of the compaction plate to prevent chipping and spalling.
Brush in kiln-dried sand to fill the joints to flush or full, compact again, and top up if necessary.
Brush excess kiln-dried sand off the surface of the blocks.
Jointing sand stabilising products are available to hold the kiln-dried sand in place, prevent migration into the laying course, and reduce weed growth. DanSand is a highly alkaline kiln-dried sand that resists weed growth.
To meet BS7533:102 adjacent blocks should not differ in level by more than 2mm.
Carry out a visual assessment of the surface course.
Surface depressions of the blocks, should not exceed 10mm when measured with a 3m straight edge.
The joints will be partially permeable for 6-8 weeks until they begin to naturally silt up. A further sanding may be necessary.
Polymeric sands may be used to joint the clay pavers.
Aftercare
Regular maintenance is key, not only to the aesthetics but also to the longevity of the patio. A light power washing, and proprietary cleaners are recommended. The joints must be topped up with sand at regular intervals, especially after power washing.
Any deterioration should be attended to as soon as possible.
