There are a variety of reasons it might be needed to conduct a the installation of a wall tie to repair it. The most prevalent reason is corrosion of the wall tie in which the wall tie was not adequately secured against rust. Galvanisation that was not properly done along with the usage of bitumen-based paints were solved in the early eighties . nowadays wall ties are made of made of stainless steel.
Other causes to rectify the issue include improper installation during construction, missing tie-ups or ties that aren’t long enough for enough embedment into one or both leaves an interior wall.
What could be the cause of problems when remedial wall tie installations are made or replacements to wall ties are made? The first thing to consider is what kind of wall tie for remedial use should be employed?
What is the most suitable cavity wall connects?
A great place to take a examine the various types of wall ties for remedial use as well as their pros and cons can be found in Building Research Establishment Digest number 329 (2000). It can be downloaded from the BRE shop. It gives a good description of the most basic kinds like:
Mechanical expansive ties are made by inserting them into the hole that has been pre-drilled and expanded to fix them to the leaf (combinations are available, that provide mechanical expansion at one side and possibly an adhesive resin fix on the other)
Resin bonded Ties : a broad range of Helical and stud/bar based rods of steel that can be placed into clean pilot holes already filled resin inside the leaf and then injected into the outside leaf upon inserting
Friction fix or Screw-in type of wall tie
Grouted sock anchors are socks that have been anchored, the grout is injected via the rod that is hollow, or through an individual feed tube, the grout being held within the expanding sock in its liquid form, and then curing to form a firm mechanical/adhesive fix.
Specialised remedial ties that can be used when one of the walls is missing, or where bricks are taken away to reveal the other leaf (sometimes known as starter tie). They can be shot fired, mechanical (steel only) and screws-in (timber frame) or resin bonding.
The type of ties that is needed will depend on the structure of walls. Mechanical ties should be installed in solid and strong materials; brickwork, fairly solid blocks, or concrete. In soft materials, mechanical ties can have a lower performance due to the greater tension they place on. In these instances, an unexpansive remedial tie like an item made of resin or a grouted sock will provide more performance.
For hollow units , a professional is required to assist select and perhaps proof-test the tie system proposed. It is not advisable to pick a replacement tie system based on price or availability. The right tie selection is essential.
One word of warning Cavity Wall insulation.
When cavities are filled prior to work on the remedial wall ties being carried out, special attention is required. Drilling holes into the insulation can cause compression and possibly contamination in the filled. BRE 329 (2000) gives suggestions on how to reduce the risk of this. If you do not take the current CWI into consideration will make the installer accountable for any damage that results due to mould or damp. Bridging between cold and damp can result from poor repair of wall tie installation.
The installation of remedial tie ties can be problematic and there is a wealth of documented instances where remedial work has not been completed correctly. Here’s a checklist that can help to ensure that the installation goes smoothly
Check that the ties were selected with a proper method and not picked randomly out of thin air.
Be sure that the installation method is compatible with the specifications of the manufacturer. All the necessary fitting tools including the resin, tension testers, as well as torque wrenches are present and calibrated as necessary. First, agree on the performance requirements. Do you require one or greater than 1Kn?
The proper drill bit’s length and diameter. What is a hammer, rotary or percussion?
The density of the installation is determined by a variety of factors. Make sure the agreement is made in writing.
The job isn’t too difficult and once the system is in place, there is no way to verify that the system is working – therefore include a test and inspection process. It is best to choose a contractor that is endorsed by recognized trade associations and consumer schemes (Trustmark, Chas, PCA, The Wall Tie Installers Federation, Which? Trusted Traders etc).
For guidance , a RANDOM 5percent testing of the remedial tie is adequate for a domestic property that is a single-use. If large-scale projects and multi-storey buildings are involved, this might be diminished over time, dependent on the outcome of the tests early on (it could also rise when defects are discovered).
Keep track of the tension test results as the work progresses
A guarantee must be requested for. Insurance can be purchased to cover repairs to wall tie-ups for up to 10 years (GPI or equivalent).
What could go wrong during the the wall tie installation phase?
Tension tests aren’t at the performance levels agreed upon.
If , for instance, the ties are reaching 800N, but not 1000N?
All accepted proof tests must already contain a ‘factor for safety’. Are the actual levels within the limits of this? If it is, it might still be enough. But, in these situations, the amount of tests needed should be increased to ensure you are sure that the five percent of 800N aren’t the highest of tie-ups. The safety factor includes a provision for lower performance. If you’re currently testing at a minimum level – 20 percent or more must be assessed. The percentage could decrease in time as work progresses, provided that all ties are at the new minimum.
What else can we do? It is possible to enhance the performance without having to buy other types of tie. Examine the method of installation The correct diameter holes? Correct depth? Are the holes clear prior to the tie being put in? Does the leaf that is hidden inside the same material, or does it differ? What is the case with grouts and resins? Are they up to date and mixed and injected properly? Does the size of the cavity changed in such a way that the amount of embedment is less – maybe a tie that is longer similar to one of these could help?
If refining the design is not able to produce an enviable improvement, there are now two options:
Modify the tie’s specification to another
Increase the density of the installation to take into account the decreased performance.
The replacement tie for the new one will be determined by the cause of failure. The increase in density of the installation should be carried out with the approval of an engineer with structural expertise. The engineer will inform the increase in density through calculation. This is crucial because when the density of the installation is too high it could result in negative unintended effects. For example , too many ties can create excessive rigidity in the cavity both in a horizontal and tangential manner, that could lead to cracking. If the density isn’t sufficient , the system will not provide sufficient support for the exterior cladding. An engineer can tell this. Do you think it is wise, for instance to increase density in the event that there is cavity wall insulation? Absolutely not.
If the tests reveal an extremely high rate of failure it is best to abandon the remedial method and return to the start. It is extremely rare when a sound procedure has been followed from the beginning. But, if wall ties are chosen due to the fact that they’re in stock my friend told me they’re top of the line or they were the most affordable, it’s likely that it will happen.
The Law.
Every construction job is covered by The Construction (Design and Management) Regulations 2015. This includes even minor residential jobs that you might find on your street. The contractor must always offer the client an health and safety record at the end of the job. The file should contain the type and quantity of wall ties that were installed. Anyone who will be interacting with the project in the future should be aware of the existence in the system by referring to this document. In the event of a house fire has occurred, it could cause a weakening of a resin-bonded tie system, which must be inspected. Conducting further modifications to the home could disrupt a remedial system especially if portions of a wall are destroyed.
Each repair of a wall tie requires working at heights. This poses a risk to wall tie professionals as well as those working in the ground. Safety and health is everybody’s business. However, it’s also an excellent indicator to determine how attentive a contractor might or might not be present on the job site. Proper preparation and care for the safety of workers and their families is an essential legal requirement with severe sanctions for not complying. Yet, poor health and safety is prevalent in construction sites, particularly residential and domestic construction. With this in mind, it’s logical to think that contractors who make a mess on safety and health regardless of the risk may even be unable to pay concentration on work, which is a possibility to hide, and could not be discovered to be in need of for a long time after he’s removed from the job location.
I’m hoping that the simple advice can help builders, homeowners , and developers make sure that their remedial wall tie projects succeed.
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