The failure of wall ties has become a significant problem in recent years. The main cause of failures is the rusting of metal ties, although there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.

Cavity walls were constructed using metal ‘ties’ straps known as fishtail or Butterfly were laid across the two skins approximately 3 foot (900mm) apart horizontally and 18-24 inches vertically (450-600mm). Wall ties are used to hold the internal and external walls that make up a cavity wall together as a single unit. Over the years, wall ties have been made from a variety of metals. The most common being metal covered in zinc or bitumen. Whereas today there are either galvanized steel of Stainless Steel.
The older metal ties, over time, begin to rust and fail.

So, if you notice horizontal cracks approximately 450-600mm apart, then the likelihood is the wall is suffering from wall ties failure.

In order to address this defect, you will need to employ the services of a specialist.
The Building Research Establishment (BRE) set guidance for surveyors to determine the level of corrosion on an inspected wall, from level 1 to 9, which gauges the severity. Level 9 is – very rusty and in need of urgent repair.
To determine the condition of the old ties they are located using a metal detector. Then holes are drilled into the wall in various locations and a boroscope is used to view the ties.
Once the condition is determined the surveyor will prepare a report and quotation to remove all the old ties and install new.
The work involved to remedy the situation is that all the old ties need to be located and removed, or isolated, and new ties installed.
There are various ties available today, Mechanical, Helical Screw-in or Resin.
The prices are similar, it’s just a matter of which system your specialist uses.
The new ties will be installed in the frequency determined by the current building standards which currently is 450mm vertically and 900mm horizontally and the holes filled with sand and cement or dashing to match the existing finish if you are intending on re-rendering.
If you do not re-render the house will look like pretty awful, and besides it’s highly likely that the render has become hollow due the rain so if you are assessing a house and suspect wall tie failure you should allow for the render to be hacked off and re-rendered, which will require scaffolding.

If you have cracks in your wall that don’t conform to those mentioned above check out my blogs on subsidence and the different causes here http://www.propertyexpertpartnership.com/2019/09/17/subsidence-part-1/
Why not check out the new edition of my book which has a complete section on building regulations and some great real-life case studies?
Get your copy here http://www.propertyexpertpartnership.com/book
Join me and other like-minded individuals in my Facebook Property Group. A great chance to ask your questions, network and keep up to date on the latest legislation and events. Join here http://www.propertyexpertpartnership.com/fb-refurb-group
Thanks for reading.
Mike Woods, MCIAT
