Inboard cutting – making the adjustments required to regular patterns so that the units can fit the space.
Technical – Each unit that is to be included should be suitable to carry the traffic load in accordance with BS 7533‚ if it were to be used as the principal paving material.
Aesthetic – While ensuring always that the technical requirements are achieved‚ otherwise the intent is to achieve the highest visual quality in the surface. On many occasions this will be specified and drawn by the designer. Where this is not done‚ the following principles should be followed. It should be noted that this may require the purchase of a small amount of specific larger units‚ both to lay and from which irregular pieces can be cut. In the more difficult situations‚ consideration may be given to changing the shape of the area to be laid to achieve an acceptable result.
Rows with staggered joints
- When rows start and run at right angles to the edge‚ alternate rows should begin with units of different lengths in order to gain the necessary stagger in the joints without using small or unsightly pieces. If the units are square in plan‚ alternate rows should start with pieces of length equal to 1. 5 times the standard dimension (+ half the joint width if this is visually significant). If the units are rectangular in plan and laid with units with length equal to twice the width‚ alternate rows may be started with a unit which is square. In either case‚ it is equally acceptable to have two special units in one row‚ at opposite ends‚ and none in the next row or one in each row but at alternating ends.
- When rows do not run at right angles to the edge‚ but at not more than 45 degrees away from the right angle‚ large enough units should be used to start rows such that‚ when cut down to fit‚ they have not less than half the area of rectangular flags‚ slabs or setts and not less than the area of square units. In the case of square units‚ larger pieces from which to cut will be required and need to be purchased specifically.
- When the rows are laid with units of varying lengths‚ cutting of any pieces at the end of the row should be done such that the resulting area of the cut unit is not less than that of the smallest in the range of units.
- In any case where a unit is trapezoidal‚ no point should have an angle less than 45 degrees. The pointed end of any such points should be cut back until the minimum width is at least either half the width of the unit or 100mm whichever is the smaller. The resulting void should be filled using an oversize unit from the adjoining row. Should this be impossible to achieve if there is no adjoining row‚ unless all traffic can be excluded from the location‚ then either the area to be laid with this material should be adjusted or‚ if the shape of the layout is critical‚ consideration should be given to the specific needs of the situation perhaps using another much stronger material such as steel or cast iron.
- Should the design require visible joint lines to continue‚ even where it is necessary for technical reasons to change the shape of the unit‚ false joints may be used. These are grooves of the same width as the joints but only shallow. False joints can weaken the stone‚ so that will need to be assessed to ensure that the resulting unit is still technically competent and in accordance with the requirements of this standard. Consideration should be given as to whether false joints can be cut on site or whether the joints should be cut into the units by the supplier.
Areas laid in a grid
- Trapezoidal shapes should be dealt with in accordance with the guidance for rows with staggered joints
- If the space to be filled is rectangular but not such that whole units can be utilised‚ consideration should be given as to how to lay the units to ensure that any pieces at the end of the rows are at least half the size of the standard units.
- False joints may be utilised in accordance with the guidance for staggered rows