Reinforced single skin concrete masonry (concrete block) construction using 200 mm wide concrete blocks that were developed during the 1960s continued into the 1970s (Figure 1).

Figure 1: Single-skin concrete masonry construction (Architect: Peter Beaven).

It was popular for its relatively low cost, ease of construction and ability to provide interesting architectural textures and finishes.

It was also used frequently for foundation walls, and basement, garage or party wall construction, particularly as it required no formwork and minimal scaffolding.

Concrete blocks are more porous than other forms of concrete and the mortar joints increase the porosity because fine cracks develop between the mortar and the blocks as the mortar and blocks dry and shrink.

Concrete block wall construction

Walls were built on in-situ reinforced concrete or concrete masonry foundation walls with concrete footings.

Reinforcing

Walls were reinforced with horizontal and vertical reinforcing.

Horizontal reinforcing typically consisted of 10 mm diameter reinforcing bars at 800 mm centres (every four courses), and vertical reinforcing of 10 mm diameter bars at 1.0 m centres.

Additional horizontal reinforcing was placed at corners and around all openings.

Reinforcing bars were lapped by at least 40 rod diameters for plain bar reinforcing and 30 bar diameters for deformed bars.

The cells of the blockwork containing reinforcing were required to be filled with grout - other cells may have also been grouted but not always.

Continuous reinforced bond beams, the same width as the wall thickness and either concrete masonry or in situ concrete were required at the tops of walls and at each floor level.

Windows and doors

Proprietary blocks such as rebated head jamb and sill blocks were available for the windows and doors.

Insulation

The early concrete block construction did not provide or incorporate any insulation. As concrete is a poor insulator (R 0.11 for 100 mm, concrete-filled blocks; R 0.19 for 200 mm, concrete-filled blocks) this often caused serious condensation problems on concrete block external walls.

The insides of the walls were often strapped (usually with 25 mm, and occasionally 50 mm, timber strapping) and lined with insulation material between the lining and the blockwork.