Positioning Wall Ties
When wall ties are bedded, they should not slope towards the inner leaf; instead they should be horizontal or, at worst, slope slightly towards the external leaf of the cavity wall. Wall ties must have a firm bedding of at least 50mm (62.5mm is recommended) into each leaf of the cavity wall, and the bedding should be even on both sides. When placing ties, they should be pushed into mortar beds after spreading to ensure that they are firmly fixed within the joints.
Wall ties are positioned 900mm horizontally, 450mm vertically (six courses of brickwork or two of blockwork) and ‘staggered’ over the face of the wall. Staggering ensures a consistency in the support provided by the ties, and allows for an even distribution of the load between the two leaves of the cavity wall. Without this approach, cavity walls would
Fig. 171 Bedded wall ties.
When openings for doors or windows occur they represent an effective point of weakness in the structure. Wall ties must be placed within 150mm horizontally of the reveal and every 225mm (three courses of brickwork or one of blockwork) in height near the sides of the openings. This is often
referred to as ‘doubling up at openings’ (see Fig 172).