Block Paving – Concrete
The depth and strength of the foundations under block paving will depend on the intended use (see Bases & Sub-bases plus Driveways Depths of Foundations).
Concrete block pavers are cuboid in shape, usually 100mm x 200mm x either 50mm or 75mm thick. Sold in packs, or by the square metre, in a variety of colours, ranging from dark grey to black, heather, red, yellow or in shades of brown, they are a versatile product range available from several different companies. Thicker versions are available, although for domestic driveways, these should not be required. They are manufactured up to 120mm deep for commercial heavy duty projects. All block paving should conform to BS EN 1338.
They are made using Portland cement mixed with coarse aggregates, quarry dust, water and colourants. Cast into moulds, they are universal in shape and size within fine tolerances, making them ideal for close contact laying. Some have small ‘nibs’ or spacers on their edges to allow for a 3mm gap in which fine silica sand is brushed to ‘seal’ the finished surface of a project.
They may be laid in a variety of patterns, although for areas likely to take heavy loads, it is advisable to avoid patterns such as basket weave, or soldier course/stack bonds where cross joints or straight lines occur, which become weak points, easily disrupted by turning wheels. The most popular patterns are either herring-bone (a zig-zag style) or half bond, mimicking brickwork, both of which provide a very strong job, unlikely to be troubled by sideways migration if laid and edged correctly (see Edging Restraints).
Take care, when laying, to draw blocks from two or more different packs, as any slight colour variations in the product batches may become apparent during the laying operations. Be aware too, that the coloured dyes used during manufacturing fade after a period of being exposed to sunlight, and future seamless colour matching is very difficult to achieve.
It is not uncommon to see some concrete block paving units laid upside down following completion of a project, and care should be taken to avoid this error.
Block paving may be sealed after completion (see Sealants – Post Laying) to reduce staining by oils or stains such as may be caused by plant sap or bird droppings.
