CONTROL JOINTS AND BRICKFORCE
All masonry types move to some degree. Clay masonry expands over time, whilst concrete masonry contracts in the same way. In addition to the basic material characteristics, all exposed walls will be stressed and destressed, by the daily and seasonal effects of the sun, wind and rain, irrespective of walling type. Walls are therefore designed and constructed with the adequate provision of vertical control joints and horizontal reinforcing. Wall reinforcements do effectively counteract the natural movement behaviour of walls. The primary objective of control joints is to divide the wall into separate panels in such a way that stresses along its length produced by differential movement can be relieved. As a general rule, vertical joints to accommodate horizontal movement should be provided at intervals of 6m to 7m.
Since there could be several variables involved, other acceptable spacing may be recommended by professionals. SANS 10145 permits joint spacing up to 9m for unreinforced masonry and up to 18.4m where vertical spacing of horizontal reinforcement is 200mm or less (subject to the length of the wall not exceeding twice the height of the wall).
Control joints are typically not required for interior walls of dwellings and buildings as these are not exposed to the effects of repeated heating and cooling to the extent of the exterior walls. Control Joints should be shown on drawings and then be built into the wall during construction and should run the full height of the wall. Sawn joints are not only costly but largely ineffective and are not recommended. Care needs to be taken that control joints extend through any plaster applied and control joints should NEVER be plastered over.
BRICK FORCE (HORIZONTAL REINFORCING)
There are two fundamental types of horizontal reinforcing. 75mm wide brickforce is suitable for imperial size masonry only. Modular masonry, being 90mm, 140mm and 190mm widths, require a different width of brickforce as per the table below. Brickforce should be made of the correct diameter wire (2.8mm-3.5mm) and should be ordered in the appropriate size (width) for the product being used. Brickforce supplied in rolls is largely ineffective and should be ordered as straight sections of 2.4m
lengths. The purpose of brick force is to limit horizontal movement and when the rolled type is laid out on the wall it does not lie perfectly flat, but has an element of wavelike curvature to it. This allows a degree of horizontal lengthening when the loading is applied, rendering the brickforce ineffective. Brick force needs to be fully embedded within the mortar and must not merely lie on top or below it.
Incorrect brick force selection and control joint detailing as well as the lack of Lime in mortar is the primary cause of both structural and surface cracking of masonry.