Natural Stone – Patios & Driveways
Depending on the intended use of a paved surface, a number of factors should be taken into account when selecting and installing porcelain. Firstly, select the correct thickness of paving for surfaces end usage, be this driveway, patio or pathway. A driveway should be laid to a minimum 30mm thick slab. For standard patio, this should be normally be laid with a 20mm.
Patios
Design and Installation Factors and Considerations
10 years or so ago most natural stone paving was laid to random pattern (see figure ). These days single sized units seem to be the preference or random sized packs of paving laid in rows (see figure ).
Important things to consider when laying to a random pattern are, no straight lines over 1800mm, no cross joints, keep the joints tight and no more than 15mm and no less than 10mm and don’t lay two slabs the same size adjacent to each other. Cross joints are not random in a random pattern, on a driveway they also affect the structural integrity of the driveway.
When laying in rows such as half bond or 1/3 offset bond. Set out the area so as not to have small 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.
Should a stack bond be chosen as the laying pattern, sawn sided paving slabs should be selected due to their minimal dimensional tolerances, noting it may still be necessary with + paving tolerances to lay adjacent units closer together and nip dow joints with a cut off saw to make them even. A stack bond is not suitable for driveways as it does not offer sufficient structural integrity for the turning wheels of vehicles.
When installing sawn and riven natural stone, a minimum fall of 1-60 should be installed to each of the subgrade, the MOT type 1 base, the bedding mortar and the surface course. British Standard BS7533:102 recommends 1-60 as a minimum.
Drainage must also be considered, especially where paving meets a lawn. If there is no drainage at the bottom of the end of the fallthis can often cause a wet, boggy lawn. For large patios, drainage should be installed at every 10m of fall.
Natural stone may also be pre-sealed to reduce maintenance.
Check Points
Firstly its important your supplier purchase ethically sourced stone, this should be checked.
Upon delivery of your paving slabs paving , it is vital to check that all crates are colour matched on the information given on the crates of paving and visual inspection upon opening the crates.
Prior to installation ensure the finished level of the paving is 150mm below the damp proof course of the house and preferably falling 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 row of paving falls away from the building, then a channel drain installed, and the rest of the paving fall towards the channel drain (see figure ).
Excavation (assuming 20mm slabs to be laid)
The minimum excavation depth is be 150mm to accommodate 100mm compacted depth of MOT type 1, 30mm bedding mortar and 20mm for the paving slab. The thickness of the geosynthetic membrane and bonding mortar is approximately 3-4mm.
If you are unsure about the strength of the subgrade conduct the heel test as outlined in British Standard BS7533:102, and adjust the depths of excavation 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 patio base, it is best practice to first lay a geosynthetic non-woven membrane to prevent fine particle migration into the subgrade. The geosynthetic membrane should overlap by a minimum of 300mm.
Good practice, especially on poor subgrades, is to install geogrid/biaxial mesh. This is specifically designed for soil stabilisation and reinforcement. Again geogrid should be overlapped by a minimum of 300mm and suitable zip ties installed to connect them together.
Best practice is to install edge restraints prior to base and sub-base installation so as to provide sufficient load baring support and resist lateral force. The edge restraints should be laid to a concrete bed and haunch and should be below the bedding mortar/laying course.
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 in depth 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 there will be no lines in the MOT type 1.
It is good practice to ‘dip’ the base, which is a method of installing to parallel string lines. Usually the first string line would be 150mm below the damp proof course, and the second running horizontaly 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 – Bedding Mortar
Set out string lines to levels and falls. The string line should not touch the edge of the pavers 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.
Bedding mortar should consist of 1-4 Ordinary Portland Cement (OPC) and one of the following aggregates: 2-6mm, 1-4mm or 2-8mm crushed rock. The mortar mix should have sufficient water added to hydrate the cement and form a ball that holds its shape in your hand when compressed with your fingers. A wet or semi-dry mix is more than acceptable, but not a dry mix.
The mortar beds should be prepared flat (see figure ) with no trowel marks (see figure ), as this will provide a full contact mortar bed. Full contact mortar bed are essential to provide full surface area adhesion between the back of the slab and the mortar bed: voids may cause reflective staining in natural stone and occasionally concrete slabs, and may also cause weak spots. Under no circumstances should paving be laid to dot-and-dab or spots.
The thickness of a mortar bed should be a minimum of 30mm and no more 40mm. As an approximate guide, mostly depending on the moisture content of your mortar mix, 35-40mm will compress to 30mm. It is important to compress sufficiently the mortar when using your rubber maul to achieve sufficient strength.
A good practice is to install geogrid/biaxial mesh to the mortar bed, especially on poor subgrades. This is in addition to that that may have been installed beneath the MOT Tyoe 1 base.
Mortar in ambient temperatures is workable for approximately 2 hours, after that a new mix is required. It is considered bad practice to keep adding water to rehydrate the mortar as the mortar loses strength.
There should be no organic matter such as leaves on the type 1 base prior to laying mortar.
Laying Paving Slabs
Paving slabs should be selected from a minimum of 3 crates to avoid colour banding issues.
Wash the calibration dust, loose debris off the back paving slab, in some cases a brush or sponge may also be necessary to remove thicker layers. If dust and dirt are not removed this can affect adhesion. It is important to also remove any wrapping or packaging material from the slabs.
Paving slabs should always be stacked vertically on timber skids to avoid chipping or damage.
The back of the paving slabs should be fully coated with a British Standard BS7533 certified bonding mortar/slurry primer, applied with a grout flat at 1-2mm thickness (see figure ).
The British Standard BS7533:102 tolerance for level variation between two paving units is 2mm.
A consistent joint width of 10-15mm is best practice. As there are generally dimensional tolerances of +/- 5 it is good practice to use a string line to check, periodically, that joint lines are straight horizontally and perpendicular. Measuring back to the base line, to make sure the paving is square or parallel is good practice. Usually measuring back would involve measuring at either end and in the middle as a minimum.
Using a washboy, clean the paving of mortar or bonding mortar as you lay.
Rake the joints out of mortar as you lay the paving, so a full joint of grout may be installed. Do not wait until the end of the day as the mortar is likely to have hardened.
The paving should not be walked on for a minimum of 24 hours. Clients should be made aware of this and paved areas cordoned off.
Jointing
Allow the mortar bed to cure sufficiently prior to grout installation this can be up to 28 days in some instances. Read the manufacturer’s specifications or contact their helpline for guidance as needed. If you grout before the mortar bed has sufficiently cured you may get efflorescence staining or water staining.
The use of single part vacuum packed brush-in grouts are not recommended.
Check the weather forecast. If rain or freezing temperatures are imminent then delay grouting.
Check the joints are of sufficient depth to receive the grout, usually a minimum 20mm depth.
Clean the surface of the paving to ensure there is no contamination of the grout.
Using a leaf blower remove excess water from the joints and surface of the paving.
Install the chosen grout as per manufacturers’ specifications, ensuring the joints are full with no voids.
Aftercare
Regular maintenance is key, not only to the aesthetics but also to the longevity of the patio. A light power washing, proprietary cleaners are recommended. Regular brushing/sweeping to remove dirt and debris build up and proprietary cleaners are recommended and. Should any deterioration arise they should be repaired immediate.
Under no circumstances should brick acid be used on natural stone.
Breatheable may be applied to the paving if not already presealed.
Driveways
Whereas the installation process is virtually the same on a driveway as a patio, there are some critical considerations and specifications to be made and implemented.
Design Factors & Considerations
Often, the falls on a driveway are governed by the levels of the garage floor and the pavement. Consideration should be given as to whether an adequate fall can be achieved as porcelain paving surface tension can hold water this may cause a slip hazard, especially in freezing temperatures.
Colour of paving slabs should be carefully considered. Tyre marks on lighter coloured porcelain will be very unsightly and can be difficult to remove.
A minimum 30mm thick paving slabs are recommended for driveways.
Sustainable Drainage System (SuDS) compliance regarding water management is required in the installation of a driveway, ensuring water dies not run onto the highway. Aqua cells, which act in a similar way to a soak away, are often used to manage driveway surface water run-off. Aqua cells should be installed 5m from the property and 2m from a boundary. A minimum B-125 specification channel drain should be used on a driveway.
Consider the laying pattern to be used, such as half bond or 1/3 offset bond. Set out the area to ensure no small cuts of less than 1/3 at the edge of the paved areas. This is not only for aesthetic reasons but also for the structural integrity of the paving. If small cuts less than a 1/3 cannot be avoided, the ‘inboard’ cutting technique should be employed. Inboard cutting is an installation technique which eliminates small cut pieces at the edge of driveway that are usually structurally weak, and it replaces those small cuts with larger cut pieces. This often means making small alterations to the laying pattern, which is why the initial setting out important.
The British Standard BS7533:102 tolerance for level variation between two paving units is 2mm.
A stack bond is not suitable for driveways as it does not offer sufficient structural integrity for the turning of vehicle wheels.
As per patios, minimum fall of 1-60 should be installed to each of the the subgrade, the MOT type 1 base, the bedding mortar and the surface course. British Standard BS7533:102 recommends 1-50 but accepts 1-60 as a minimum.
Excavation and Base Installation
Firstly, locating piped and cable services – such as gas, electric and broadband – and their depthsis essential. A CAT scanner and Genny cable detectors are recommended. The white service boxes at the sides of newer properties show where cables and pipes enter the ground: digging carefully beneath them to locate the depth at where the pipe bends is a good indication of their overall depths.
Inspect manholes with regards to their depths to ensure that sufficient Type 1 base depth can be achieved. The structural condition of manhole chambers should be checked: often on old properties the mortar perishes between the bricks and when compacting around chambers this can cause damage and collapse.
Consider the weight of the homeowners’ vehicles, such as car, van or even motor home. Vehicles heavier than a standard vehicle will alter the design of driveways based on: refer to British Standard BS7533:101 for guidance.
The bare minimum excavation depth for a porcelain driveway is 210mm: 150mm MOT type 1, 30mm mortar bed and 30mm paving unit, assuming standard vehicle usage.
Install edge restraints to retain the driveway on a concrete race and haunch to a minimum of 50mm up the side of the edge restraint.
For compaction, use a double-barrelled roller in 100mm layers, or forward and reverse diesel whacker 40/60 plate in 70mm layers.
If you are unsure about the strength of the subgrade, conduct the heel test as outlined in British Standard BS7533:102, and adjust the depths of excavation accordingly to meet the design specified in British Standard BS7533:101.
The fall of the formation level should match that of the surface course.
Compact the subgrade.
Base – Sub-base Installation
Best practice would be to install a geosynthetic non-woven membrane to prevent fine particle migration into the subgrade. The geosynthetic membrane should overlap by a minimum of 300mm. Indeed, good practice, especially on poor subgrades would be to install a geogrid/biaxial mesh. Again geogrid should be overlapped by a minimum of 300mm and suitable zip-ties installed to connect them together.
Install MOT type 1 to a minimum, consistent compacted depth of 150mm, at the same fall as the subgrade. The MOT type 1 should be installed in layers no more than 70mm in depth 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 there will be no lines in the MOT type 1.
It is also good practice to “dip” the base which is a method of installing to parallel string lines. Usually, the first string line would be 150mm below the damp proof course and the second string line placed at the bottom of the patio 150mm from the subgrade, with the line pulled taut every 1m to ensure an even distribution of Type 1 with no humps or hollows. Should there be low spots, these can be filled with Type 1 and compacted, high spots may be raked to low spots or levelled.
Laying the Natural Stone
Set out string lines to levels and falls. The string line should not touch the edge of the pavers 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.
Bedding mortar should consist of 1-4 Ordinary Portland Cement (OPC) and one of the following aggregates: 2-6mm, 1-4mm or 0-6mm crushed rock. Sharp sand is also an option: do not use builders’ sand as it lacks the strength of crushed rock, often has a clay content and acts like a sponge with moisture, which can cause freeze/thaw issues. The mortar mix should have sufficient water added to hydrate the cement and form a ball that holds its shape in your hand when compressed with your fingers. A wet or semi dry mix is more than acceptable, but not a dry mix.
The mortar beds should be prepared flat (see figure ) with no trowel marks (see figure ), as this will provide a full contact mortar bed. Full contact mortar beds are essential to provide full surface area adhesion between the back the slab and the mortar bed. Voids may cause reflective staining in natural stone and occasionally concrete slabs, and may also cause weak spots. Under no circumstances should paving be laid to dot and dab or spots.
The thickness of the mortar bed should be a minimum of 30mm and no more 40mm. As an approximate guide, mostly depending on the moisture content of your mortar mix, 35-40mm will compress to 30mm. It is important to compress sufficiently the mortar when using your rubber maul to achieve sufficient strength.
A good practice is to install geogrid/biaxial mesh to the mortar bed, especially on poor subgrades.
Mortar in ambient temperatures is workable for approximately 2 hours, after that a new mix is required. It is considered bad practice to keep adding water to rehydrate the mortar as the mortar loses strength.
There should be no organic matter such as leaves on the type 1 base prior to laying mortar.
Pointing and Grouting
Allow the mortar bed to cure sufficiently prior to grout installation: this can be up to 28 days in some instances. Read manufacturer’s specifications or contact their helpline to be sure. If you grout to before the mortar bed has sufficiently cured you may get efflorescence staining or water staining.
The use of single part vacuum packed brush-in grouts are not recommended.
Check the weather forecast. If rain or freezing temperatures are imminent then delay grouting.
Check the joints are of sufficient depth to receive the grout, usually a minimum 20mm depth.
Clean the surface of the paving to ensure there is no contamination of the grout.
Using a leaf blower remove excess water from the joints and surface of the paving.
Install the chosen grout as per manufacturers’ specifications, ensuring the joints are full with no voids.
Aftercare
Regular maintenance is key, not only to the aesthetics but also to the longevity of the patio. A light power washing, proprietary cleaners are recommended. Regular brushing/sweeping to remove dirt and debris build up and proprietary cleaners are recommended and. Should any deterioration arise they should be repaired immediate.
Sealants may be applied to the materials if not already presealed.
