Special Public Works Programmes - SPWP - Stone Paving-Blocks - Quarrying, Cutting and Dressing (ILO - UNDP, 1992, 60 p.) 4. SECONDARY CUTTING AND DRESSING Product dimensions Secondary cutting of stone paving blocks Dressing the paving-blocks Tools for dressing stone paving blocks Curbstone dressing

Special Public Works Programmes - SPWP - Stone Paving-Blocks - Quarrying, Cutting and Dressing (ILO - UNDP, 1992, 60 p.)

4. SECONDARY CUTTING AND DRESSING

Product dimensions

The products most often used for road-surfacing work are the following:

Description	Dimensions in cm
	Allowance:	width (w) in cm ± 1 cm	length (I) in cm 5cm	height (h) in cm 1 cm
Mosaic paving-block		7 to 10	7 to 10	8 to 10
Large paving-block		14	20	14
Bondstone		14	30	14
Edging curbstone		16	80	20

Mosaic paving-block

Large paving-block

Bondstone

Edging curbstone

Slight deviations from the standard dimensions of paving-blocks, of around 1 cm for width and height, and 5 cm for length, are tolerable.

As shown below, two types of curbstone can be used. Apparent curbstones for use with sidewalks raised above the street surface (A) are more difficult to produce because two of their faces are exposed when they are laid. The two exposed faces should be even and form a 90° angle.

A.

Simplified cross-section

B.

Simplified cross-section

Examples of the use of stone paving-blocks

Examples of the use of mosaic paving

Arch layout

Decorative effect

Good paving must display the following characteristics:

· the road surface must be quite even, ensuring a comfortable riding surface for traffic: the distance between the bottom of dips and top of humps in the road surface must not exceed 2 cm (1) over a length of 3 meters.

(1)

· the lateral face of paving-blocks must be perpendicular to the road surface.

Road surface

Paving-blocks are laid in sand bedding

If lateral faces of paving-blocks form an obtuse angle (more than 90°) with the road surface, these must be corrected on the site to form a right angle.

Figure

Excessively wide surface joint due to poor quality of paving-blocks.

If the lateral sides of a paving-block form an acute angle with the road surface, the paving-block loses some of its stability.

Figure

As the bearing surface of the paving-block is reduced, the block will tend to sink into the bedding sand.

2 cm is the maximum separation permissible for a tapered joint.

Cross-section of large paving blocks

Very high quality bondstones

Acceptable (medium quality) large paving-block

Unacceptable paving-block: its faces do not form 90° angles, and therefore it is to be rejected.

Secondary cutting of stone paving blocks

Unlike primary cutting in the quarry where three methods are possible (quarry wedges, plug and feathers and explosives), secondary cutting of stone paving blocks involves splitting using a quarry wedge.

First, the required cuts are marked with the help of a rule and marking tools. This task must be carried out with care and precision so as to make the most of the block; the more precise this operation is, the less paving-block dressing work and stone waste there will be.

Marking the cutting-line

To split a block, the same procedure is employed as in quarrying using splitting wedges: the cut is marked by making a groove with a grooving-chisel and club-hammer or with a hammer drill equipped with a chisel end. Every 15-20 cm, wedge holes are made. Once the wedges have been tapped into place with the club-hammer, they are struck in succession with a sledgehammer, splitting the block.

Grooving a block with a hammer drill

Figure

Putting wedges into wedge holes using a club hammer

Once slabs of paving-block thickness have been produced (see drawing), a template with the dimensions of the paving-blocks required is used to mark out the cuts needed to produce the paving-blocks.

Using a template to mark cutting lines for cutting of paving blocks.

Figure

Cutting paving-blocks

Grooves are made along the cutting-lines using a grooving-chisel. These operations (marking and channelling) are repeated on all faces of the stone.

Manual grooving.

Figure

Figure

Next, a crowbar is placed under the slab of stone at the places here the stone is to be split.

Figure

Figure

The stone is struck with a sledgehammer directly above the crowbar. The shockwave produced is transmitted to the crowbar, which acts as a bearing point, causing the stone to be split at this precise place.

Figure

Figure

Safety:

As in all stone dressing work, gloves and safety goggles should be worn.

Dressing the paving-blocks

The blocks obtained from this cutting process are slightly larger than the dimensions required for paving.

The template is again employed to mark the edges of the paving-block, which are then shaped with the help of a tungsten-tipped chisel.

The projecting edge of the tool is moved to different points along the marked line and the chisel is given a single sharp blow with the club-hammer. The angle at which the tool is held determines the amount of material removed.

Figure

Cutting-edge of chisel on mark

Safety:

Stone fragments are very sharp; any wound, however small, must be treated without delay. Gloves, boots and safety goggles must be worn to minimise possible injuries. First aid kits must be available on site.

A grooving chisel is used to correct any remaining uneveness of the stone's surfaces for final, detailed dressing.

Final detailed dressing using a grooving chisel

Tools for dressing stone paving blocks

Club hammer

Grooving chisel

Double chisel

Metal mallet

Template

Punch

Tungsten-tipped chisel

The size of the template varies depending on the type of the paving block (mosaic, large, edging curbstone, etc. See page 30)

Curbstone dressing

Curbstone dressing is a delicate operation due to the larger surface area to be covered. The steps to be followed are described below.

First, a rule is used to mark the final curbstone measurements on the road surface face of the stone block.

Figure

To facilitate marking, the block can be supported on a chock, as illustrated below. Next, another line is marked along the edge of one of the faces perpendicular to the road surface face. This line is traced from the lowest (shallowest) point along this edge.

Figure

Figure

This edge is then squared using the same technique as for paving blocks; that is, using a tungsten tipped chisel and club hammer.

The same marking and dressing procedure is repeated on the opposite face. The work requires care and precision to obtain a perfectly true and smooth road surface, with no irregularities.

To proceed, the rule is placed at the lowest point on each face to make the subsequent edges.

Figure

The second edge can then be squared as before.

Dressing of the paving-block is finished off, using a grooving chisel to correct any irregularities which may still exist on the road surface face or sides of the block.

Perfectly dressed edging curbstones.

To recap, the minimum tools required by a stonemason to produce paving blocks are the following:

Description		Number	Diagram and observations
Club-hammer		1	weight 1.250 kg cost 20 $
Metal mallet		1	weight 1.250 kg cost 20 $
Steel grooving-chisel		10	weight 0.8 kg cost 6 $
Tungsten carbide chisel		1	weight 1 kg cost 50 $
Steel double chisel		1	weight 0.9 kg cost 20 $
Steel wedges		10	cost 3 $ locally produced
Marking tools
	- pencil
	- red wood
	- charcoal
	- scribers
	- stone chip
	- rule
	- metal square
Stonemason's safety goggles			cost 10$
Safety shoes			cost 50 $
Ear protectors			cost 35 $
Work gloves			cost 10$
Crowbar			can be locally produced; 34 mm, length 1,800 mm