Cavity Wall Tie Replacement
Cavity walls have been constructed since the beginning of the 20th century and were implemented to offer better protection from the elements as well as reduce the amount of unnecessary heat loss from the property.
The system comprises two separate walls, the internal and external walls which are ‘tied’ at strategic intervals using a form of wall tie commonly made of metal coated in bitumen or zinc, known as cavity wall ties.
If your property is suffering from wall tie failure then this can mean that both skins (or leaves) become independent of each other. This means that the property can become structurally unsafe and a danger to those that may be in it or around it.
What is a Cavity Wall Tie?
Cavity wall ties are metal strips or bars built into the cavity walls with the sole purpose of holding the masonry together. Wall ties are key to the safety and stability of all cavity walls. They are used to stabilise the wall construction and to stop the separate skins of the wall from moving away from each other.
The ends of the ties are designed to lock into the cement bed of the mortar joints in each skin. There is also a design element in the tie (usually a twist or dip) that stops the transfer of moisture from the outer leaf to the inner leaf of the wall construction.
Cavity walls usually now have insulation within the cavity that has been incorporated into the design of the wall construction or retrofitted with blown or foam insulation. They usually take the form of galvanised fishtail types in the earlier years and later they then were constructed from galvanised twist wire and more recently stainless steel.
Walls that are solid construction ( don’t use have a cavity ) will not have cavity walls ties within their construction as a general rule although there are some exceptions where flat steel plates have been used in solid construction walls.
Signs of a Cavity Wall Tie Failure
It is difficult to know when the cavity wall tie has failed and how much damage it has caused until it can be visually seen on the wall. The most common sign of wall tie failure is that there will be horizontal cracks on the outer walls of the building. External visual indicators of wall tie failure are listed down below:
• Horizontal Cracks – in a mortar, often at a high level, caused by the expansion of corroded wall ties.
• Bulging walls/brickwork – caused by snapped wall ties, which have corroded. This can make your property unstable.
• Bowing walls
• Lintels sagging
• Cracks or separation of the window reveals
If you are experiencing any issues we have mentioned then it is more than likely that your property is suffering from cavity wall tie failure. Getting in touch with a qualified expert will be able to diagnose the structural repair problem and recommend the best solution to treating the issue.
Carrying Out a Cavity Wall Tie Survey
A cavity wall tie survey is usually straight forward and takes around an hour or so to conduct. With the survey relying heavily on the inspection of the outside of the property these surveys have to be carried out in daylight hours. When the surveyor arrives at the property they will initially inspect the exterior of the property. In particular, they will look at the following:
• The construction of the property
• Any cracks or bulges that are visible
• Check for the presence of a cavity wall and if so if there is any insulation within the cavity
Following on from this the surveyor will then locate the exact positions of the ties by using a metal detector. This may involve the use of a ladder depending on any areas of concern identified with the initial external inspection. Once the location of a selection of wall ties has been identified the surveyor will drill an inspection hole.
To check the condition of the wall ties within the wall a borescope is used. A borescope can be viewed as the endoscope of the construction world. Where there is no insulation present in the cavity the surveyor will have a very good view of the wall ties as the borescope illuminates the wall ties.
The condition of the wall ties can then be graded in line with digest 401 published by the Building Research Establishment. This document explains how to grade the condition of the wall ties as well as recommending actions that need to be taken. There are nine classes of wall tie ranging from 1 where the wall tie is showing no signs of corrosion and shiny through to 9 where there is visible corrosion to the ties.
Other factors are also taken into consideration by the surveyor such as the type of wall tie, the number of wall ties used, the presence of cavity wall insulation and the general exposure of the building to the elements.
In cases where there is cavity wall insulation present, a borescope surveyor may not be possible and a more invasive method of checking the condition of the wall ties may be required.
Cavity Wall Tie Replacement
The extent of the wall tie repairs and replacements must be first checked by a qualified professional. High-quality metal detectors and other specialist equipment are then used to safely and effectively assess existing cavity wall ties. Fibre optic boroscopes are also used to assess the condition of the wall ties.
Once the condition of the existing wall ties has been identified then the technician will install the replacement wall ties. New stainless steel wall ties are installed by usually drilling from the external leaf and fitting replacement wall ties in a pattern to match current Building Regulations.
This is usually 450mm staggered centres and at 300mm centres vertically at opening such as window and doors. The wall ties will be positioned so they are staged from the original damaged cavity wall ties. The new replacement wall ties can be either mechanically anchored or fixed with resin.
Types of Replacement Cavity Wall Ties
There are three types of cavity wall ties that can be effectively fitted into your wall and these are:
Mechanical Wall Ties
Mechanically expanding ends is a key feature of these ties, and this allows them to effectively lock into your walls. Immediately after fitting, you can load test the tie to ensure it’s been correctly fitted.
Resin is used to bond this cavity wall tie to its base material. If the base material is less substantial or unable to take on the stress, this can prove to be an excellent solution.
Combination ties (Resin/Mechanical)
This is an incredibly robust solution for buildings that are made from mixed materials and this can give you the support and structure that you need.
Quality you can trust: To ensure that the cavity ties are correctly locked in place, we conduct random insitu load testing, so you will have peace of mind that your ties reach the required standards across the board.
Cost of Wall Tie Replacement
The cost of cavity wall tie replacement can vary from a number of factors and these can be dependent on how many wall ties need replacing to how severe the problem is.
Our team at Timberwise have a number of cavity wall tie specialists across the country who will assess the severity of the problem and provide a reasonable cost to fixing the damaged walls of the building by replacing the cavity wall ties.
Need A Specialist Who Can Install A Cavity Wall Tie?
Timberwise has fully trained and experienced surveyors across England, Wales and Scotland who have a range of solutions at their disposal to solve your cavity wall tie problem. Our surveyor will recommend the most suitable structural repairs for your property as well as provide a written report for the work to be carried out.
If a problem with cavity wall tie corrosion has been identified, our specialist technicians will provide the right treatment to your corroded wall ties. Contact Timberwise by calling on 0800 288 8660 or you can request a survey online.