Landscaping & Paving Glossary (Pavasaurus)

1. Sub-base – where the aggregate, MOT Type 1 (Type 1 SHW clause 803) has not been properly compacted, leaving air voids in the sub-base. These generally occur when an installer tries to compact too greater depth of hardcore in one go. Rather than trying to compact 150mm of MOT Type-1 at once, three consecutive 50mm layers can be compacted, to ensure each layer is fully compacted. This approach will mean there is less chance of any air voids being formed.
2. Laying course – where the installer has used either dot-and-dab or framing of the bedding mortar rather than a full bed of mortar to lay the slabs. Both dot-and-dab and framing should be avoided as the air voids create a range of potential issues (including weaker bonds, more chance of slabs coming loose, damp and water filling the voids creating staining, efflorescence, chemical and physical erosion and also differential weathering for concrete slabs that cure unevenly due to damp and water pooling in the voids).

Its main use is as the aggregate in concrete, where its larger particulate sizes means it creates a stronger, more durable structure good for footings, foundations and base slabs.

The functions of the bedding layer are:

• To allow paving units to be adjusted to level
• To be shaped so paving units can be manipulated and laid in desired locations
• To support the paving units
• To provide a cushion between the paving and the sub-base

For patios slabs, a full bed of paving mortar (5:1 ratio cement mix) is used as the laying course.

For driveway block paving, a bed of screen sharp sand is used as the laying course.

• 5 parts sharp sand
• 1 part general purpose cement
• water (just enough to mix the mortar, e.g. it should be a relatively dry cement mix)

Bedding mortar should be used in conjunction with priming slurry to ensure that there is a very strong bond that will prevent your paving coming loose.

As well as being used for driveway paving, block paving is also commonly used in landscaping for garden pathways, borders and edging, often being used decoratively for paving features, patterns and motifs.

Most bricklayers nowadays will also use a mortar plasticiser additive to the cement mix that will make the mortar much more workable (more cohesive and elastic).

• Brick & block laying mortar
• Masonry mortar
• Render
• Plaster

In landscaping when we refer to cement, we generally mean Portland cement, a fine grey powder manufactured from common minerals (Limestone – CaCO3, Alumina source – Al2O3 Iron ore – Fe2O3 and Silica source – SiO2) which are mixed together and fired in a kiln to ± 1450°C to create a binder with hydraulic properties called clinker or k. Clinker is an intermediate product of small lumps or nodules of heat fused material. This clinker is crushed and ground into a fine powder (usually with 5% gypsum added to prevent flash setting) to create Portland cement.

There are five types of cement used in the UK under the B.S. EN 197-1 standard:

• CEM I – “Pure” Portland clinker: with a maximum of 5% minor additional constituents (Ordinary Portland Cement / OPC).
• CEM II – Composite cement: Portland clinker + upto 35% additives (e.g. fly ash, slag or limestone).
• CEM III – BFS-OPC: blast furnace slag cements (type A 35-64% clinker, type B 20-34% clinker, type C 5-19% clinker).
• CEM IV – Pozzolanic cement – pumice or volcanic ash (type A 65-89% clinker, type B 45-64% clinker) – see Roman concrete
• CEM V – Composite cement

Breeze is an older name for ash/cinder, which is often a constituent material in their manufacture. This, is the origin of their common name, breeze blocks (and hence why the common American name for them is “cinder blocks”).

They are generally sold as either low density, medium density or dense and common strength ratings are 3.6N, 7.3N and 10.4N. The common size formats are:

• 440 x 215 x 100 mm
• 440 x 215 x 140 mm
• 440 x 215 x 215 mm Hollow
• 215 x 215 x 100 mm Course Adjusting Brick
• 350 x 300 x 100 mm Foundation Block

Their function is structural. For double-skin walls, they will generally have an either exterior skin of facing bricks, or be directly rendered or clad to provide an appropriate aesthetic. For interior walls, stud work & plaster board or plaster are used to provide an appropriate finish.

Generally, delamination is a minor issue, and the underlying paving slab is left unaffected and sound.

Sedimentary rock is layered over time in sheets of sediment which fuse together under gravity, pressure and chemical bonding to become laminated (layered together).

When chemical erosion (e.g. acid rain) or physical erosion (e.g. freeze-thaw) of paving stones occur, the outer layers of the laminated rock structure are weakened and flakes of rock will become loose and detach from the slab (delamination).

Don’t worry too much about delamination – it is a natural process, and the slab is usually unaffected when smaller flakes come away.

Do be carefully with high-pressure washers, as these can get between layers of rock on a riven surface, and weaken the stone, and cause delamination.

What causes these differences in concrete moisture that trigger differential curing?

• Water pooling and damp from voids in the bedding layer (dot & dab / framing)
• Surface water pooling & poor drainage (improper fall/gradient and dips in the patio level)
• Bedding mortar moisture transfer when the mix is too wet
• Subsurface moisture uplift/osmosis where a priming slurry or SBR bond has not been used during installation
• Items left on the concrete patio when it is first laid (timber, plastic, pallets & packs of building materials)
• Splash zones from blocked/obstructed down-pipes and guttering

• Issues #1 – voids under the slabs: moisture can pool, creating damp patches & discolouration
• Issues #2 – voids under the slabs: moisture/damp can erode and weaken the slab (chemical and frost-action erosion)
• Issue #3 – voids under the slabs encourage burrowing animals and weed growth
• Issue #4 – weak bonding with the slabs – loose slabs, rocking slabs and trip hazards
• Issue #5 – unsupported slabs – larger spaces / voids between the supporting bedding mortar dots increase the chance of slabs cracking under load (e.g. traversing with a heavy wheelbarrow or similar load).

The format of driveway paving blocks is smaller and thicker than a patio slab. The smaller surface-area and added depth of driveway pavers means they are able to handle higher loads and greater compression. This prevents them from shearing or cracking under the weight and movement of vehicles.

An edge course fulfils multiple functions:

• Structural – used as edge restraints, the haunched course holds block paving in place
• Practical – edge of a pavement is laid intact, creating a neat, orderly edge (e.g. no cutting or irregular sizes)
• Practical – they make cutting in the pavers easier (giving you a profile/guide against which to mark & cut)
• Practical – the edge restraints are laid and haunched before installing block paving, so they can be used as level guides when screeding the sharp sand bedding layer.
• Aesthetics – they provide a visual border or picture frame to the paved area, better defining the space.

The edge will be slightly sharper and more angled than a tumbled edge, and the profile line along the edge of the paver will be truer/straighter than a tumbled paver.

Hand-cut paving will tend to be laid with medium width joints (standard jointing).

Because both mechanical saws and water jet cutters came into being during industrial mass production and industrial digitisation respectively. Consequently, straight sawn edges are associated with modernity and contemporary aesthetics, as this is when they came into consciousness in architectural and hard landscaping.

Straight sawn edged pavers can be narrow jointed as their edges offer more precise laying options, although butt-jointing (where paver touch each other) should always be avoided.

A tumbled paving slab has a softer, more rounded profile where the sharper edges have been smoothed and worn off during the tumbling process.

Tumbled edge slabs and blocks will tend to have wider joints when laid, as edge profiles and less true and more irregular.

Kerbstones or larger blocks will be used as edge restraints and laid on mortar. Once properly positioned and levelled, the restraint blocks will be haunched with concrete.

The kerbstones/restraint blocks can be used as level guides when you come to screed the sharp sand for the laying course.

During the warmer conditions of the day, melt-water then drains down further into the porous stone or concrete. That night, this water reforms as ice, which then expands within the capillaries, fissures and cracks, widening them, weakening the stone or concrete, and the freeze-thaw cycle of erosion continues.

In the United Kingdom, where average winter humidity is >85%, there is ample moisture and damp that will be present in the
capillaries, micro-fissures and cracks of stone or concrete if left unprotected. It is recommended to use an impregnating sealer on porous stone and concrete to help prevent water absorption, and consequently reduce the effects of freeze-thaw cycle erosion.

The gravel/aggregate should be coarse and washed (with fewer fines) to prevent the pipe perforations from becoming clogged. It is more common nowadays to see the pipe wrapped in geotextile permeable fabric to add improved protection to prevent clogging from fines.

Granite is very hard, dense and has very low porosity, being in-fact relatively impervious. Granite has excellent dimensional stability too.

As one of the best performing natural stones from a paving perspective, granite is only really surpassed by porcelain. That quality comes at a price though, and granite will tend to be more expensive than other natural stone.

There are typically two colour of granite paving that are widely used in landscaping and paving, although others are available:

• Silver Granite
• Black Granite

Granite paving slabs and granite setts (stone block paving) are both common and widely used.

• Jointing Block Paving

• Paving Slabs: laying course of 5:1 mortar (40-50 mm depth)
• Setts: laying course of 5:1 mortar (40-50 mm depth)
• Cobbles (river stones): laying course of 5:1 mortar (40-50 mm depth)
• Block Paving (concrete, stone & clay): laying course of compacted sharp sand (50 mm)

However, the properties that make this mortar less likely to be selected for everyday use, are actually why it is still ideal for certain projects. Lime mortar is especially useful in the repair, restoration and conservation of period and historic buildings. It breathability, weaker relative strength to old bricks and masonry (as a sacrificial component) and flexibility are key characteristics necessary when restoring older properties or using older/traditional construction techniques.

Limestone is a relatively soft stone (Mohs hardness of 2 to 4), but has excellent compression strength (up to 180 MPa compared to concrete at approximately 40 MPa). This means it is ideal as a material for paving, as it is soft enough to cut and work, but very strong when used as paving under compressive load.

Limestone is generally light coloured, in a white to light grey range. However, darker types such as Black Kadapha and Kota Blue are found when the organic content of the rock is higher.

Limestone paving has a distinct “orange peel” texture finish when riven, and feels soft and tactile. This finish makes limestone paving a popular choice and explains why it has been used in this role for millennia.

The road is constructed with a compacted sub-base of a coarse aggregate (20 – 75 mm) comprising low porosity angular stones. The angular stone lock together to form a stable mass. On top of this, a wearing course of a finer aggregate, also of angular stones that would form a solid interlocking mass when compressed, is added. This construction method was highly reliant on the grade of the aggregates and their angular shape to ensure stability and longevity.

• Bedding layer – mortar is used for the bedding layer/laying course on which slabs, cobbles or setts are laid. The mortar adheres the paving in place and provides strong bonding and stability between the paving and the sub-base.
• Structural bond – mortar is used to bond masonry together (stone, bricks or CMU/breeze block) and provides structural cohesion e.g. when bricklaying the mortar bonds the bricks together.
• Pointing – mortar is used to point more traditional paving such as stone cobbles and setts. Mortar is most commonly used to point walling such as garden retaining walls, knee walls etc. The role of pointing is four-fold:
  1. to fill the joints/voids between masonry units
  2. to prevent water ingression
  3. to be weaker than the surrounding masonry so it can be the sacrificial element that (as the cheaper material) is the easiest to remove/replace when repairs are needed
  4. to provide the aesthetic finish to the masonry.

Cement mortar using Ordinary Portland Cement (OPC) is the most common type of mortar used in landscaping and paving. For period restorations, building conservation and traditional builds, a lime mortar is often used or required.

There are generally five main types of wall capping:

• Cock ‘n’ hen capping – a vertical “dry-stone” style line of stones laid perpendicular to the line of the wall that form irregular peaks akin to the “comb” on a chicken’s head.
• Pitch face, half-round capping – dressed stones laid perpendicular to the line of the wall that have a hand-cut pitched or chamfered profile to achieve a rounded cross-section.
• Hogs Back / Half-Round / Rendered – – similar to pitch face capping, but either dressed stone (hogs back) or pre-cast half-round concrete laid in-line with the wall, custom render formed into a half-circle.
• Tiles / Slabs – One of the most common forms of capping is the simple use of tiles or paving slabs to line the top of a wall. Usually laid length-ways along the wall.
• Brick / Block – probably the second most common form of wall capping is the use of bricks or blocks. Usually laid in a soldier course perpendicular to the length of the wall.

There are five general types of coping:

• Flat – a simple slab of concrete or stone
• Contemporary Apex – four sloped sides meeting at the middle like a gentle pyramid
• Neo-Classical Apex – four sloped sides meeting at the middle with neo-classical style cornice & entablature
• Stepped – like a step-pyramid, with each square level getting successively smaller
• Ornate – often with a neo-classical entablature and pediment, upon which an ornate element such as an urn, obelisk, orb, or eagle sits in the centre.

In architectural masonry, jambs will often be used in conjunction with other matching window surround elements, with window cills and head having matching styles to create a unified look.

One of the major advantages of cast stone when used in archirectural masonry is the colour control achievable through pigements used in production. This allows architects and builder to carefully select exactly the colouring they need for their building’s stonework.

When external air flow is not directional towards the vent, but running perpendicular to it, the vent is still able to successful draw air from the roof space as it exploits the Bernoulli Principle (where faster moving air has a lower pressure), so the external low pressure turns the vent into a venturi (acting like a vaccum cleaner) and sucks the warm, humid air out of the roof space.

Kneelers are most commonly seen on gable coping where they sit at the base of the gable’s triangular shape supporting the rising coping stones.

Historically, wall plinths were designed to protect the base from damp and rain-splash. As walls generally used lime mortar, the plinth base was both breathable and thicker/ more robust, thus, achieving the aim of providing better damp protection.

However, as contemporary construction generally builds cementitious walls (which do not breathe like lime mortar walls), plinth courses are largely decorative, providing a more traditional / period look and feel, but serving little functional purpose.

Datestones are not very reliable as historical records of the age of a building, as often they are reused when a building is rebuilt, so bely the real age of the property, often predating the existing structure.

The Balusters themselves can be simple turned stone (rounded/cylindrical in nature) or intricately carved (squarer, more geometrical in nature).

The purpose of the balustrade is aesthetic; it is there to add beauty, intricacy, craftsmanship, order, and create a sense of wonder/import.

This construction aggregate grade contains fines and is graded from 40 mm to dust.

Type 3 SHW clause 805 has reduced fines, which means it is suitable for permeable paving and underground water collection systems as the reduced fines will not clog or inhibit drainage.

The solution to this issue is to replace the patio’s pointing with a waterproof replacement (epoxy based jointing compound).

As with all coping, the function of a pier cap is to protect the brick/masonry pier from the effects of weather, and prevent rain and damp getting into the pier and causing damage to its structural integrity.

Sandstone is a relatively hard stone (6-7 Mohs hardness) but its compressive strength (20 – 180 MPa) and flexural strength (5 – 30 Mpa) can vary widely depending on porosity and the amount and type of cement and/or matrix material present.

Sandstone is the most commonly used natural stone for patio paving. Most sandstone paving slabs in the United Kingdom are presently sourced from quarries in India.

Sandstone colouring ranges from light creamy yellows through to blacks and dark greys. The most common and popular sandstone paving colours tend to be fossil (light gold), buff (golden yellow to light tan), Kandla grey (light silver/dove grey to mid-grey), Raj/Autumn (light browns, chestnuts and sienna).

Sandstone slabs will generally either have a riven or honed surfaced finish. The edge finish will usually be one of three options; sawn (straight), hand-cut (near straight with small deviations) or tumbled (more rounded edges and corners with greater deviations on the profile).

Sandstone is also used to make setts and paving blocks, and these can also vary in finish, edge profile and calibration.

Other common landscaping products made with sandstone include edge stones and kerbs, coping stones and pier caps, garden features (spheres, benches, plinths and sculpture bases).

The two most popular types of setts used widely across the UK for driveway and garden paving projects are sandstone setts and granite setts.

As well as being used for driveways, garden borders, and potting beds, shingle is often used for underground drainage as support material for pipes and soak-away chambers.

• Concrete
• Paving Bedding Mortar
• Block Paving Laying Course

• Spots/stains where the mortar is drawing water from flooded voids up into slabs
• Damage to the sub-base and mortar from water in the voids, causing subsidence and instability
• Damage and loosening of the slabs, from freeze-thaw action from water collecting in the voids
• Higher risk of unsupported slabs cracking where the voids are not supporting the paving
• Insect infestations likelihood is higher as the voids provide the perfect home for ants and other insects.