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Most homes built in the last hundred years are of cavity wall construction: the external walls are built of two leaves of brickwork linked with metal ties. The main purpose of cavity construction is to improve the walls weather resistance, keeping your home warmer and drier than a solid wall construction.

Wall Ties are generally made of mild steel and the most common forms of tie are the 'fishtail' or vertical twist ties (either galvanised or bitumen coated) and the galvanised butterfly wire tie. These mild steel ties are however susceptible to corrosion and it is this defect that can lead to structural problems as the corrosion causes the metal ties to expand. The evidence of the tie expansion can be seen as horizontal cracks in the mortar bed joints and even diagonal cracking across the face of the brickwork. In very extreme cases bowing of brickwork or even partial collapse of the outer skin of brickwork is possible.

Our survey will not only examine for evidence of wall tie corrosion, but also that the quantity and spacing of ties is correct. Structurally, the cavity wall is a load sharing system and ties must be laid out in a uniform spacing pattern: (diamond formation with ties at 900mm centres in courses set 450mm apart). At door and window openings this spacing is reduced to 300mm vertically. Typically, large walls that are exposed to the weather and small areas of brickwork e.g. Over door and window openings are most vulnerable to structural movement and therefore the correct quantity and spacing of ties in these areas is important. Structural damage from wind suction in these exposed areas is more likely if there are either insufficient or incorrectly spaced ties.