- A specification has to cover the quality of the block materials to ensure their long term durability, retention of adequate slip and skid resistance, but also consistency of their physical dimensions and uniformity of shape.
- Stress caused by blocks being too close together, resulting in movement from horizontal forces, is minimized by chamfered edges which provide a "cushion" between the blocks.
- The ideal joint range is between 2 and 5mm. The space of a joint should cater for dimensional tolerances, deviations in layering, arising for the laying pattern and possibly the setting-out of edge restraints. If joint widths exceed 5mm then the structural ability of surfacing decreases.
Figure 2: The bond shown is a herringbone pattern, in which rectangular blocks are laid in a combination of headers and stretchers. The image displays a common joint misalignment that will always occur when the block's length equals twice its width.
Figure 3: This image further depicts the need for a standard spacer on interlocking blocks. The irregular block shape, which is not commercially available, is also laid in a herringbone fashion here. The "gearing" together of these blocks makes for consistently growing joint widths as the blocks are laid.
Conclusion: The examination of the laying modules, figures 2 and 3, illustrates the need to design blocks with a peripheral space of half a joint width from all block sides, which is shown in figure 1.
Check out the entire "Size and Block Shape - Do They Matter" pdf by clicking here.