Wall ties are an important part of cavity wall design. They are used to join the inner leaf of the load bearing leaf of the building to the outer leaf of the building. This ensures structural stability. Wall ties are usually made from stainless steel because it is corrosion resistant. However, this is not always the case. Some older buildings may have wall ties made from other materials.
How does a wall tie failure occur?
Wall tie failure occurs where existing wall ties have corroded or where insufficient or incorrectly installed wall ties cause the failure. Mild steel or galvanized steel wall ties corrode and rust (also called iron oxide) builds up on them, causing them to expand. The resulting pressure on your surrounding masonry can cause cracking in your mortar bed. Wall ties can also expand in your external wall and bulge out of the brickwork. Wall tie failures can also be caused by poor installation during construction. It is important to ensure that you install the correct wall tie for your building, the type, the height and the location of your building, and a tie that is long enough for the cavity of your building. If left unchecked, wall tie failure can lead to serious structural issues including, but not limited to, the potential for a dangerous collapse of your outer leaf of your masonry.
What are the signs of wall tie failure?
When a wall tie corrodes, thick layers of iron oxide build up and make the tie thicker than it would be if it were made of steel. When this happens over and over, the force can actually tear the wall apart, causing cracks in the mortar bed where the ties are stuck. Wire ties don’t usually have the same weight to cause the same cracks, and they can erode completely without anyone noticing until the wall bulges or buckles. The worst areas for wall failures are where there’s a lot of brickwork and no return, like brick panels between windows and at the top of gable walls.
What is the solution?
Installing remedial wall ties and then removing or isolating existing wall ties is the fastest and most economical way to replace wall ties. There are several types of remedial wall tie, but the top three are:
Mechanical Expander Replacement Wall Ties
Mechanical expander retrofit ties are threaded bar ties with sleeves that are inserted through pre- drilled holes. The ties are twisted to tighten the sleeves.
Resin or grouted replacement tiles
When resin (or grouted) ties are set into place, they’re anchored into place. The only downside to these types of ties is that they’re not great for installing cavity wall insulation.
Helical replacement wall ties
Self-tapping Helical Ties can be used in the majority of wall tie replacement applications. Helical Ties gain stability by cutting the substrate when powered, resulting in a secure mechanical connection.
Replacing a wall tie isn’t something you can do on your own. You’ll need a structural engineer, a surveyor to determine the best tie for the job, and work like this should be done by an approved installer.