If you have an older property with masonry walls, it’s likely that a surveyor will recommend a wall tie survey. They do this for a very good reason – wall tie failure is a common issue in older homes and can cause serious structural problems if left untreated. But it can be a bit confusing to hear. What is a wall tie? How do they fail? What damage do they cause? And what can be done to fix them? That’s what we’re here to talk about today.
Cavity walls are built of two leaves of masonry with a gap between them. Wall ties are a crucial part of keeping these cavity walls together – they’re made of metal and connect the inner and outer leaves of the cavity wall to make sure they act as a single, structural unit. This cavity can then be filled, or partially filled with insulation.
Modern wall ties are made of stainless steel, with the ends bedded into the mortar joints at regular spacing. A drip prevents any water from crossing the tie to the inner leaf (as long as it’s been laid level and doesn’t have any lumps of mortar dropped on it). However, older ties might be made of galvanised metal wire like butterfly ties, or even older ungalvanized or coated iron-based metal fish–tail type ties.
Wall tie failure can significantly compromise a building’s structural integrity. The main cause of wall tie failure is corrosion, particularly in older buildings. When older ties rust, they expand to several times their original size, which can crack the mortar joint and lose its bond. Particularly on more exposed elevations that get wet often.
Rust expansion of wire ties isn’t much of an issue in itself, but they are more prone to fail. The reactions between different types of material used on some mortars (and in exposed coastal areas) can be problematic. Any ties used in or around the 1970s had a reduced standard of galvanising, and more prone to failure. And in older houses it’s common to not have the number or regular spacing of wall ties found in modern construction.
Despite being embedded into the wall, there are telltale signs that your wall ties are failing. The first sign is usually horizontal cracks along the mortar joints, often at regular intervals along the walls. If your home has wire ties, issues can be more difficult to detect as they don’t always cause cracks in the external walls. Because wall strength is weakened without wall ties, you might also see bulging or undulating walls as they start to move. In the worst cases, parts or all of the external masonry lead can collapse.
Since wall ties are embedded in the wall, finding them usually required a metal detector. Once we’ve found the right spot, we then inspect it using a borescope or camera. This is usually enough, but there can be problems if the cavity wall is full of insulation, as this can hide the damaged tie so that it isn’t visible. If this is the case, then we may have to do a full inspection, which means exposing the ends of the tie by either removing some mortar or brickwork.
The existing wall ties should be removed, ground off or isolated form the external wall, depending on what the most practical method would be for the circumstances. The external mortar will be made good and weathertight after that. The condition of the ties will then be assessed, and depending on that we will either recommend remedial action or periodic inspection.
Yes! But it’s often not simple. Normally the repair process involves drilling into the wall at regular intervals and fixing new stainless-steel ties into both wall leaves. This can be done by a few different methods including resin fixed, hammer driven or expansion, which is decided by the suitability of the walls. Once the new ties are fixed, the holes are sealed. There is a slight risk of any debris in the cavity falling to the base during the fixing process. This can be easily removed from the base of the cavity (or elsewhere) to reduce the risk of dampness.
If you think you have issued with your wall ties, it’s always worth having a survey done. At Harrison Clarke, our building surveyors regularly undertake thorough building surveys, and any risks of wall tie or other structural failure will be considered. We’ll only recommend further investigations if we think they’re necessary or prudent. If you’d like to know more, you can contact our team on 02381 550 051.
For more expert advice on surveying and property matters, check out our range of informative videos on our website or YouTube channel. Harrison Clarke Chartered Surveyors is here to guide you every step of the way!
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