Paving

Figure 1: Finished paved driveway

Image from pavingexpert.com

This blog examines the key materials and processes in paving.

Working Safely

Like any building work, it is important to be aware of the risks when paving. Excavating brings about many risks such as making contact with underground or overhead power lines. Excavation related accidents account for 7% of all construction related deaths (Flavin and Leavy). It is important that proper precautions are taken on site and that all workers have proper experience and have received training. Before starting any excavation, a survey of the site should be carried out to determine the hazards, what precautions should be taken and what protective clothing should be worn.

Underground services from about 1985 onwards are normally ducted as follows, which helps identify the potential hazard:

- Electricity supply is normally coded red

- Gas pipe (yellow)

- Telephone cable (grey)

- TV cable (black)

- Water pipe, made from lead (blue)

- Drainage pipes made from PVC (concrete, clay)

Figure 2: Protective Clothing

Image from Irishconstruction.com

Examples of protective clothing (Figure 2) that should be worn when carrying out excavation work include:

• safety boots, or wellington boots for concrete

• gloves

• dust masks when using power saws to cut paving materials or when working with cement

• safety goggles when cutting materials

• overalls or standard work-wear

• hard hat for overhead works or trenches

Power tools are another source of danger in paving and hazards include noise, vibration and probably worst of all, entanglement. All users should be therefore properly trained and take the following precautions:

• check the date of the last inspection of any machinery

• keep cables off the ground

• do not overload sockets

• do not adjust a power tool until supply is disconnected

• do not overreach

• use a transformer when required

Figure 3: Con-saw

Image from hirehere.ie

An example of a power tool commonly used in paving is con-saw, (Figure 3) a hand held cut-off saw which can be electric or petrol operated. Petrol operated con-saws should not be used in unventilated areas. Another example is block and slab splitters (also known as guillotines), which come in a range of sizes, and can handle materials from bricks to flagstones.

Paver Patterns

Figure 4: Paving patterns

Image from selectpaving.ie

There are limitless patterns that can be made with pavers. Figure 4 displays 10 different paving pattern or bonds. The most common bonds used in paving today are:

• 90 and 45 degree herringbone (zig zag pattern)

• Basket weave (two horizontal bricks, then two vertical)

• Running bond or stretcher bond (rows)

Pavers Types

When choosing a paving type, the visual characteristics, the cost and the durability should all be considered. Vehicular paving has to be far tougher than pedestrian paving.

There are four main types of pavers: brick, concrete, natural stone, and cobblestone/cobble lock.

Brick

Figure 5: Laying a brick driveway

Image from Pavingexpert.com

When paving, ensure that any bricks used are suitable for paving. Some bricks intended for housebuilding will not withstand the wear and tear that paths and patios are subject to. Bricks can be made of clay, or concrete with a pigment for colouring. They can be laid on their edge or flat, and laying them flat is the more economical way to lay them. Figure 5 shows a brick driveway.

Figure 6: Concrete slabs

Image from Drivewaypaving.ie

Concrete slabs (Figure 6)

• can be reinforced and non reinforced

• comes in any colour or shape

• can be key jointed or filled by capillary action

Figure 7: Limestone slab

Image from midland-stone.com

Natural stone slabs/ flagstones

• can come in any colour or shape; for instance sandstone normally comes in earthy tones and limestone (Figure 7) often comes in yellow or grey

• normally kept small for easy handling

• jointing in is usually done with mortar

• not suitable for areas of high traffic as it can break

Figure 8: Cobblestone

Image from Stockys.com

Cobblestone / cobble lock

• Cobblestone (Figure 8) is a natural stone material such as granite and is a very traditional method of paving in larger cities such as Temple Bar in Dublin

• Cobble block is a modern copy of cobblestone and it is made of concrete. Its aim is to mimic natural stone, but in its uniformity it tends to fail to achieve this

• both are laid using a running bond

How to Lay Paving

Figure 9: Plans for a Driveway

Image from Pavingexpert.com

1) Measure The Area

Mark out the area of paving using sand, a spray marker or string and stakes. Consider what is the appropriate width for any pathways and if there is enough room for two people to walk side by side on the pathway.

To set out a straight line:

- Position the start and end pins

- Pull a string line tight between the two pines

- Add intermediate pins so that they are just touching the taut string line

To set out a perpendicular:

When laying bricks in line with a wall or a house, it is useful to know where the perpendicular line is. The information required to do this is that any triangle that has side lengths in the ratio of 3:4:5 is a right-angled triangle. For example, measure a distance along the front of house of 4 metres. From one side (side 1) mark a 3 metre ark, from the other end (side 2), mark a 5 metre arc. Where the arcs intersect is the apex of the triangle. Fix a string line from the apex to side 1, and this is a perpendicular

To set out arcs and curves:

The method using a measuring tape or trammel:

• Anchor the tape measure the origin point, measure the desired length and swing the arc around

• An S-curve formed by linking two arc going in different directions

2) Decide on Paver Laying Method

There are two main methods of laying pavers and these should be decided before any excavation begins:

1. Rigid paving has a concrete base and is suitable for areas of heavy traffic. Mortar or grit sand is used on top of the concrete. Expansion joints are required for rigid paving to absorb the expansion and contraction of building materials. An example of rigid paving is cobbles set in concrete.

2. Flexible paving has is no concrete base or mortar and can respond to expansion and contraction with temperature change and to some degree vertically in the event of different settlement (Blake, 1999). An example of flexible paving is crushed stone and stabilised gravel (Blake, 1999).

3) Installing Sub-base and Drainage

Figure 10: Spreading the sub-base

Image from Pavingexpert.com

The area should be excavated to a depth so that the finished paving level will be 150mm below the damp-proof course (DPC) level of the building. Consider space for the hardcore, cement, mortar, sand, as applicable, and paving block heights.

In order for water to run off naturally from paved areas, an appropriate fall is required. The fall of the paving is the gradient. Very often, insufficient attention is paid to this and the result is muddy puddles gathering in areas, making the paved surface slimy and sometimes impassable. The fall should be directed away from building or towards a shore. The recommended fall is between 1:40 to 1:80. A 1:80 fall means that for every 80 units of run, there will be one unit of rise. The formula for establishing the fall is:

Distance divided by 1/Gradient = Fall.

So for a 5 metre run length and a desired gradient of 1:80, the fall will be 5000mm/80 = 62.5mm.

A driveway may have two slopes: one towards the footpath and one towards the gullies at the house. The house may then have two slopes, one toward each gully at each side of the house.

Transferring levels is the process of transferring a height or level to another spot in order to measure elevations correctly. The first step is to determine a basic level from which all measurements for the building can be taken. This basic level is called the Datum level/peg and is normally the DPC level.

Figure 11: Transferring levels using a water level

Image from diydoctor.com

The main methods of transferring levels on site are:

• levelling board with spirit level placed on top

• three boning rods in the shape of a T and all the same length. Put first two close together at the same height. The third rod is put further away and the sight line of all three together is determined

• water level: this is using a length of rubber hose with a glass tube at the each end. When the two glass tubes are at the same level, the height of water will be the same. This method is useful when levelling points which are not visible from each other, eg around a corner. See Figure 11.

Once the excavation has taken place to the correct level, spread and lay sub-bases at the required falls of the paving.

Install any drainage that is required and haunch with concrete. The paving should fall slightly towards either drainage channels, a gulley drain, a lawn area, or the footpath.

• Fill any voids with course sand

• Spread, level and compact bedding sand to correct level

4) Laying the Paving Slabs

Lay the paving slabs on either sand or mortar, and tap down firmly after laying, or alternatively use a flat-plate vibrator. Leave a small gap in between slabs to be later filled with mortar or dry jointing sand. When all blocks are laid, check for alignment with a taut string line, then adjust as necessary and cut edges.

Concreted bedded edgings (Figure 12) and kerbs are used wherever a rigid support or restraint is required at the perimeter of a pavement. They prevent the paving from spreading and causing a series of problems such as vehicular traffic forming indents or weeds growing in the loose joints. They are also an attractive design feature and help define the edge of the paving and mark out the perimeter.

The most common kerbstones/edgings are

• brick kerb

• concrete kerb

• bullnose kerb

Figure 12: Edging

Image from pavingexpert.com

REFERENCES:

Blake, J. (1999) Landscape Design and Construction. Hampshire, England: Gower Publishing Limited.

Flavin, N. and Leavy, S. (2018) A Review of Construction-Related Fatal Accidents in Ireland 1989-2016, Health and Safety Authority. [online] Available from <https://www.hsa.ie/eng/publications_and_forms/publications/construction/a_review_of_construction-related_fatal_accidents_in_ireland_1989_-_2016.pdf >[accessed 28 March 2021]