How to spot wall tie failure
Outwardly-visible signs of cavity wall tie problems are largely dependent on the composition of the building and on the type of wall tie used in its construction. The main things to look out for are;
- A pattern of horizontal cracks – a tell-tale sign of wall tie corrosion issues
- Bowing or undulating wall surfaces – a tell-tale sign that the outer wall is not tied back to the structure
As wall tie corrosion develops, bulky iron oxide layers accumulate to expand the thickness of the tie to several times that of the original steel. When this ‘expansion’ is repeated along a row of ties produced from steel plate, the combined force can actually split the wall causing horizontal cracks along the mortar bed joints in which the rusting ties are embedded.
Wire ties do not generally have the mass to produce the same wall-weakening cracks and often these ties can completely erode with no visual sign of a problem until the wall starts to bulge or buckle.
The wall areas most vulnerable to resulting wall failures are those where there are long spans of brickwork between corners and those where there are no structural returns, such as brick panels between window openings and at triangular gable apex walls.