Block Beauty

With the right specification, exposed blockwork can not only be durable and cost-effective, but beautiful too, writes Elaine Toogood

The specification and detailing of concrete blockwork masonry is more akin to brickwork than other concrete products, and focuses on product selection rather than custom design. Choosing the right block is critical. A wide range of colours and textures are available, and while block dimensions are standardised, it is possible to commission bespoke shapes for special elements in a design. New products are also constantly evolving.
Architectural facing masonry is blockwork specifically designed and manufactured to be left exposed, combining structure and surface finish. Its uses range from landscaping features and robust internal partitions to the external or inner leaf of cavity wall construction. An assortment of natural stone colours and textures, such as split-faced or shot-blasted, are available, providing a cost-alternative to stone, but the aesthetic options extend much further to include a range of bold solid colours and polished and honed surfaces.

The typical grey blocks used for internal structural walls can also be left exposed without detriment to structural performance, but a more appropriate aesthetic solution is to specify paint-grade or fair-faced blocks, which have a smooth, more closed texture. If more than one face is to be exposed, this must be stipulated from the outset. Where continuity of colour is required, fair-faced blocks should be sourced from a single location.

Design guidance

The choice of bond is a fundamental aesthetic and structural design decision. The simplest, most cost-effective option is stretcher bond but other patterns and arrangements are possible. Some blocks are available with profiles to help mask the typical stretcher bond pattern – for example, those with grooves to mimic stack bonding. Setting out walls and openings to suit coursing and unit dimensions is critical and should be considered as early as possible. It is essential to elevate walls to identify the need for any special sizes and to avoid or minimise cut blocks. Factory-cut blocks are recommended for visual blockwork.
Mortar joints should be specified and installed carefully to achieve not only the correct strength but also colour consistency and weathering performance. Dry silo or ready-to-use mortars are recommended. The joint profile, whether bucket handle, flush, struck or weathered is a key aesthetic decision and should take into account both the surface texture of the block and exposure conditions. It can be a challenge to achieve a quality finish using flush joints, especially with textured blocks; thus they are not normally recommended for fair-faced blockwork.

Consideration should also be given to the location of vertical and horizontal movement joints so that they are integrated into the overall design, rather than being an afterthought. Vertical joints have the most visual impact and are typically required every 6-7m. They are also recommended at changes in wall heights, loading conditions and at abutments with other structures. It should be noted that the movement joints are required for shrinkage, rather than the expansion that is found in clay bricks. Bed joint reinforcement helps to reduce the need for additional movement joints in areas of higher risk. This includes between courses of dissimilar materials or below long windows where the aspect ratio of the walls exceeds 3:1.

It is good practice to build a control panel before works start to agree workmanship quality and assist with final detailing decisions. The panel should ideally be in a position where it can remain for reference throughout the project.

With the right materials and construction approach, beautiful, durable walls are easily achieved using exposed blockwork, especially when combined with good, creative detailing.

Further information about blockwork is available from the Modern Masonry Alliance:

Photo: Forticrete​