Movement of brickwork should be considered at the design stage. The main sources of movement referenced here relate to moisture and temperature. Other factors may relate to loading and creep, and in certain situations, it may be necessary to consider the effects of chemical action, ground movement and settlement.

In general, reversible movements are caused by temperature changes and these can be calculated by reference to the coefficient of thermal expansion, as indicated in Appendix A4 of BS 5628:Part 3 and the Ibstock Brick Design Guide on Movement. However, irreversible expansion caused by adsorption of water molecules by the fired clay brick can be larger and continue, albeit at a reducing rate, for a period of years.

The movement properties of common building materials including brickwork are set out in Table 12.

The spacing and thickness of movement joints is related to the detailed design, length and height of the brickwork, together with any requirements for structural restraint.

An indication for normal storey height walls is that the joint width (in mm) should be at least equal to the joint spacing (in m) plus an allowance of typically 30% to allow for the compressibility of the filler and the performance of appropriate sealants.

Thus movement joints at 10m centres will need to be approximately 13mm wide and the distance between movement joints should ideally never exceed 12m. Most constructions are set to a 5/6 metre grid therefore for design purposes it is normally accepted that movement joints should be considered at 10/12 metre centres. Movement takes place around corners and not just in straight runs of masonry. It is therefore important to include all continuous masonry in the assessment.

Unrestrained or lightly restrained walls (such as parapets and small freestanding walls) should be given double this amount of movement provision. In these cases, the distance between movement joints should be 5-6 metre centres, with coping and cappings at half these distances.

As indicated in BS 5628:Part 3, present evidence suggests that vertical movement of unrestrained walls is of the same order as horizontal movement. This standard also refers to the use of flexible cellular polyethylene or foam rubbers as suitable compressible materials and the use of sealants such as low modulas silicone which are suitable for sealing of movement joints. This standard also advises on unsuitable materials, e.g. fibreboard. Further guidance on the selection of sealants is given in BS 6213.

Clay and concrete units have different movement characteristics, these differences being in both magnitude and direction. They should not be bonded together but separated by either a vertical
or horizontal movement joint or by a slip plane.

When brickwork is to be used to clad a reinforced concrete frame, the design should make particular allowance for differential movement.

Detailed advice based on BS 5628:Part 3 is available from Ibstock Brick’s Technical Services Department.

Moisture Movement & Thermal Properties of Common Building Materials

Reinforcement

Brickwork is strongest in compression. The forces set up by reversible movement, irreversible movement or simply by changes in section due to door or window openings, can induce tensile forces, resulting in cracking. Such behaviour may be modified or controlled by bed joint reinforcement which can accommodate the tensile forces and help bond adjacent courses together in a homogeneous mass.

Stitching rods may be inserted and grouted into the perforations contained in some bricks to both locate and support the bricks over door and window openings. The rods should be stainless steel and used in accordance with the Structural Engineer's specification.

Mechanical Fixings

Innovative brickwork detailing, particularly corbelling that exceeds the recommendations of BS 5628:Part 3, or where the bearing for successive courses in 103mm brickwork is less than 70mm, may require proprietary channels, cranked or special shape ties and angle supports fixed back to a reinforced concrete or concrete cased steel structure. The use of an SBR (Styrene Butadiene Rubber) additive may also be considered where bricks are to be bedded on stainless steel angles.

Non-loadbearing arches, particularly those possessing a small rise in relation to their span, may similarly require additional support or restraint.

Cavity brickwork must incorporate wall ties (usually stainless steel) embedded in the horizontal mortar joints to a minimum depth of 50mm. Tie length and type (refer to BS 5628:Part 3 Table 9B) depends upon the cavity width and requirements for strength, flexibility and retention of insulation materials. Ties should be staggered and evenly distributed in accordance with BS 5628:Part 3 (Table 9A), typically at 900mm centres horizontally and 450mm centres vertically. Additional ties should also be provided within 225mm of movement joints or openings at a maximum 300mm vertical centres.