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How to succeed when installing remedial wall ties

There are a variety of reasons it is needed to conduct a an interventional wall tie installation. The most frequent reason is corrosion of the wall tie when the original wall tie was not adequately secured against rust. The poor galvanizing process 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 for remedial work are incorrect installation during construction, missing connections or ties that aren’t long enough to allow enough embedment into either or both of the leaves of the cavity wall.

So, what could be the cause of problems when walls are rehabilitated or replacements to wall ties are made? The first thing to consider is what kind of wall tie for remedial use should be employed?

Which is the best cavity wall is the best to tie?

An excellent place to examine the various types of wall ties for remedial use along with their benefits and drawbacks can be found in Building Research Establishment Digest number 329 (2000). It is available on the BRE shop. It gives a good description of the most basic kinds of bre like:

Mechanical expansive ties work by being inserted in an already-drilled hole, and then expanded to hold them in one or more leaf (combinations are also available that allow mechanical expansion on one end , and possibly an adhesive resin fix on the other)
Resin bonded Ties : a large selection of Helical and stud/bar-based stainless rods of steel that can be put into pilot holes already filled resin inside the leaf and then injected into the outer leaf following the insertion
Friction fix or Screw-in type of wall tie
Grouted sock anchors in which the grout is injected either by the hollow rod in the tie, or through the feed tube that is specifically designed for it – the grout is held in the expanding sock in its liquid form, and then curing into a solid mechanical or adhesive fix.
Specialised remedial wall ties designed for use when one of the walls is missing, or where bricks are cut to show the 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 design of walls. Mechanical ties must be used in sound and strong materials; brickwork, relatively solid blocks, or concrete. In soft materials, mechanical ties can have a lower performance because of the higher tension they place on. In these instances, an unexpansive remedial tie like one made of resin or a grouted sock, will give higher durability.

For hollow units , a professional is required to assist select and perhaps proof-test the tie system that is proposed. It is crucial not to pick a replacement tie system based on price or availability. The right tie selection is vital.

One word of warning Cavity Wall insulation.

When cavities are filled prior to repair work on the wall tie is completed, particular care is required. Drilling holes into the insulation can cause compression and may result in contamination in the filled. BRE 329 (2000) provides suggestions on how to reduce the risk of this. If you do not take the the existing CWI into consideration could leave the installer responsible for any damage that results due to mould or damp. Bridging between cold and damp can be caused by poor repair of wall tie installation.

The installation of remedial ties could be a challenge and there is a wealth of documented instances of remedial work that has not been completed correctly. Here’s a checklist that can help the installation go smoothly:

Check that the ties were picked with a sound methodology rather than just picked from the air.
Be sure that the installation method is compatible with the specifications of the manufacturer. Make sure that all the necessary fitting tools including strain testers, resins, and torque wrenches are present and calibrated if necessary. First, agree on the performance requirements. Do you require one or greater than 1Kn?
The correct drill bit’s size and length. What is a hammer, rotary or percussion?
The density of the installation is determined by several factors. Make sure the agreement is made in writing.
The job isn’t too difficult however, once it is installed there is no way to verify that the system is working – therefore incorporate a testing and inspection procedure. Choose a company that has been approved by recognized trade and consumer associations (Trustmark, Chas, PCA, The Wall Tie Installers Federation, Which? Trusted Traders etc).
To help, a RANDOM 5percent testing of the remedial tie is a good starting point for a single domestic home. If large-scale projects and multi-storey buildings are involved, this might be diminished over time, dependent on the results of the test early (it can also rise when defects are discovered).
Keep track of the tension test results while working
A guarantee must be requested for. Insurance covers repair work on wall tie for up to 10 years (GPI or equivalent).

What is the most likely issue at the wall tie installation phase?

Tension tests aren’t at the performance levels agreed upon.

For instance, if the ties are reaching 800N instead of 1000N?

Every agreed proof test should already contain a ‘factor for safety’. Does the actual amount still within the limits of this? If yes, then it could still be enough. In these instances, the amount of tests needed should be increased in order to ensure you are sure that the five percent of 800N is not the most effective of tie-ups. The safety factor is that it allows for a lower performance. If you’re conducting tests at the minimum, 20 percent or more of the time, it should be assessed. The percentage could decrease in time as work progresses, provided that all ties meet the new minimum.

What else can be done? It is possible to increase the efficiency without needing to purchase other types of tie. Verify the procedure for installation for the correct diameter holes? Correct depth? Are the holes in the right place before the tie is put in? Does the leaf that is hidden inside an identical material or does it change? What about 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 can help?

If refining the design is not able to produce an enviable improvement, there are two options available:

Modify the tie’s specification to another
Increase the amount of installation to take into account the decreased performance.

The new tie replacement will depend on the type of failure. Increased density in the installation must be done under the supervision of an engineer with structural expertise. The engineer will inform the increase in density through calculation. It is vital to note that when the density of the installation is too much it could result in undesirable unintended consequences. For example , too many ties could create excess 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 be able to support 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? It’s not.

If the tests reveal very high rates of failure you should abandon the remedial procedure 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 because they were available My friend said they’re the best , or they were the most affordable, it’s very likely that it will happen.

The Law.

Every construction job is under The Construction (Design and Management) Regulations 2015. This includes even minor household jobs in your neighborhood. The contractor should give the customer the health and safety report at the end of the job. It should include the kind and quantity of wall ties used. Anyone who will be interacting with the project in the future should consider the condition of the tie-system by referring to this document. For instance, if a home fire has occurred, it can weaken a resin-bonded tie system, which must be inspected. Making further changes to the building could alter a remedial plan, especially if walls are destroyed.

Each remedial wall tie installation requires work at a height. This can pose a danger for the wall tie workers as well as those working in the ground. Safety and health is everybody’s business. However, it’s also an important indicator when deciding the level of diligence a contractor must have or should be working on site. A good preparation and attention to the safety of workers and their families is an essential legal requirement with severe sanctions for infractions. Yet, poor health and safety is typical in construction sites, particularly residential and domestic projects. In this light, it’s logical to think that contractors who cut corners in regards to health and safety despite the danger, might even lose concentration on work, which is a possibility to hide, and might not be uncovered even after he has gone from the location.

I’m hoping that the simple advice can help developers, builders, homeowners and homeowners make sure that their remedial wall tie installations are successful.