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Understanding Cavity Wall Tie Replacement

Anyone can make a repair to a cavity wall tie, and they can be purchased online for an DIY method. Why do architects, structural engineers and local authorities’ mortgage lenders need for a specialist’s help to install this?

There are some excellent reasons …..

Cavity wall ties are essential for the security and stability of the entire cavity wall. They are installed by the bricklayer when they build the masonry, and it has been the standard procedure for more than a century in building cavity wall ties across the UK.

The process of constructing wall ties to the wall once it’s constructed is simple and there’s nothing to be wrong (though errors do occur in newly constructed homes too). However, installing wall ties on existing construction is a different matter.

Before deciding to install new remedial cavity wall ties, here are some aspects that have to be taken into consideration:

What distance should the fix ties be?
How do you think the length of the wall ties should be to fit the wall’s thickness and the length of the cavities?
How much is the building exposed and do the numbers above of wall ties have adjustment?
What is the material used for construction that is used to construct the cavity wall the outer and inner leaf (block or stone, brick or wood)?
What are the areas of wall that cavity wall ties are not permitted to be put in (there are always a few)?
Is the cavity free of obstructions or cavities wall insulation which could be contaminated due to the wall tie?
What is the best way to access the wall for secure wall tie installation, (you are responsible for your safety as well as the safety of those who are working for you)?
What diameter pilot hole does wall ties require, and how do you make it?
Are there surfaces such as render, which wall ties need to be secured through?
What is the best way to have the wall tie be tested to ensure that they are functioning?
How can the appearance and style of this building be maintained by avoiding a ‘polka dot effect?
Do the wall ties have the capacity to be able to last the lifetime of the building?
In taking the above into consideration and having selected the appropriate cavity wall tie for both the outer and inner leaf fix, how can the efficiency be monitored at the site?
Who will be installing the wall ties ? What experience has he/she received?
What equipment is required to make the pilot hole, tie them up and verify them?
What is the record-keeping and reporting procedure for test of wall ties?
What happens in the event that the remedial tie fails random testing due to unanticipated reasons ? What will this costyou?
Then, what type of assurances will be given for the materials used as well as the work, and is it an insurance-backed assurance?

There are many other questions that are more than the eighteen listed, however these questions are important ones to be asked before replacing a wall tie begins.

Nothing here is an art, but here are the short solutions to the questions above. ….

The spacing of the wall tie depends on a mix of variables that include the width of the cavity and the size of the leaf. They can vary from the typical staggered pattern of 900mm x 450mm to as small as 450×450 in certain situations. There are areas of the wall that require particular attention, for example the exposed reveals that are not tied around windows or verge locations. The density of the wall tie considers wind loads too (these are able to vary throughout the nation and also with the height). It may also take into account the efficiency/effectiveness of the tested wall tie installation. A low performance could mean more tie are required; an increase in the wall tie density. High performance may help decrease the amount of tie in the wall when an engineer from the structural engineering department has taken part in the process as well as rigorous testing on site has been conducted to verify the installation.

Make sure to note that any performance numbers provided from the manufacture are general and could not be applicable to your particular site. Only test on-site of the wall tie will reveal the true performance since the manufacturer hasn’t seen your wall and has not built it. (read the conditions and terms and you’ll see this confirmation in every manufacturer’s cavity wall tie data sheets)

The depth of embedment of ties depend on many factors too. A 50mm depth into each leaf is recommended as a minimum, however this assumes a normal brick cavity wall, and does not consider the internal spalling of the face (caused due to the impact drilling of the outer leaf, which creates the brick chip from the inside of the outer skin , thus reducing the thickness of the wall at this point). This is intended to be a guideline only, and in most cases more thorough tie penetration is required. For soft materials, such as old clinker blocks the depth of the pilot hole or diameter could require an increase (diameter increases are particularly applicable for anchors made of resin/grouted to lessen the ‘bearing’ stress). The timber frames are a unique situation, and extremely extensive, random testing is necessary to measure the depth of fixing required for a satisfactory fix for the studs of timber. It is natural substance and has a range of strength in the same building according to the sapwood content and the precision of the construction.

There are graphs that show the building’s exposure to wind gusts and naturally the load of buildings with higher rises are higher. The load is also higher in homes, where for instance , two houses are constructed with gaps between the gables (common in numerous housing estates) creating the wind funnelling effect that puts a lot of stress on the wall ties because the speed of wind decreases the air pressure and forces the gables. This requires the increase in density to increase the number of wall ties that could otherwise be required.

Wall ties must be flexible enough to allow the outer and inner skins of the wall to move differently. This is why the corners of homes must be avoided as the new ties could cause stress fractures as they are not able to withstand this movement. Any hidden utilities must be avoided as well. There should not be any pipes or cables in the cavity, however they’re more prevalent than you’d imagine and drilling into a cable to put in a cavity wall tie could result in a fatal accident.

The cleanliness of the cavity is another thing to take into consideration prior to installing the cavity wall tie. When the space is stuffed full of debris or insulation, the design will have include this. Cavity wall insulation, in particular is not considered by many wall ties installers as well as DIY homeowners. The problem is pollution of insulation. The insulation is typically older foam or modern fibre or beads. By nature, it is a flexible, light product that is designed to minimize the loss of heat and allow water vapour to flow through the cavity without restriction.

The installation of wall ties for remedial purposes can result in kind of material being ejected out of the cavity. This is the result of brick dust or stone powder (drill spoil) that is ejected from the inner and outer leaf (a 12mm hole that is 100mm wide in its outer leaf and 60mm deep in the inside creates around 19 cm3 drill spoil). However, the drill dust is air-conditioned and is subsequently weighed down by air, and the pile is much larger than the amount of dust. The majority of it is ejected out to the side walls (into your face when you drill) however, the rear portion (including any face that is spalled that could be large, see the previous paragraph) as well as all of the excrement from the interior leaf, are blown in the cavity. It’s not a problem when the cavity is empty, as dust won’t be able to cross a damp proofing course, or cause the bridging. However, it is a different matter for the cavity with insulation.

In the cavity that is insulated, the drill spoil is unable to be removed and remains in place. The result is similar to an unclean snowball. There are a few at every wall tie position and at each wall tie isolation point in the case of isolating the cavity wall tie too. The consequences on insulation can be severe.

It is compressed due to material, making it more dense than. Additionally, the debris transfer water and heat extremely efficiently. Therefore, a couple hundreds of wall tie could significantly reduce the effectiveness of insulation. The loss of heat isn’t as significant in terms of financial cost however from a condensation standpoint, it can cause issues. A few minor variations in the insulation cause cold spots appear (surveyors refer to this as cold Bridging) and be caused by high humidity lead to mold growth and damp patches to appear on the interior of walls. The situation gets more severe …. leaving debris in place allows water to move through the cavity (cavity bridge) and can exacerbate the problem by soaking the insulation, or in extreme cases , creating penetrating damp inside. All cavity wall ties that are remedial include a drip feature. They vary in design but all function by causing rainwater to run off the wall tie, before it has the chance to get to the interior skin and create damp. In insulation that has been contaminated, the drips just fall on the’snowball’ that has been contaminated, and worsen the situation.

If there is insulation, additional measures should be taken to minimize the risk of contamination in the cavity, such as changing methods of installation, and also removing obstructions, and implementing additional measures on the spot.

Secure access for wall tie replacement.

The installation of wall ties requires drilling using both hands at heights across the building. The risk of falling from a height remains the most fatality during construction, and the most frequent causes are ladder accidents as well as DIY accidents. Testing of wall ties requires hands and photographs or notes are required to be taken. This is why an elevated scaffold or fixed tubular scaffolding is necessary. The possibility of hitting hidden service lines implies that only double-insulated equipment and 110v centre-tapped to earth machines need to be taken into consideration. The condition of the soil and slopes, as well as overhangs; overhead power cables and obstructions like conservatories , are just a few things that a skilled wall tie expert will be aware of. The presence of customers, children or visitors working on the job is crucial too. The site is extremely noisy and it can also be dusty.. It is important that neighbors are informed.

If the wall has been rendered pebbled, pebbled or coated with something that is reflective of the way to install the wall tie and the kind of tie used to repair it. First is the wall’s material in good condition? Drilling can cause vibrations and could break or loosen old render. There could be pipes or services under the coating? A metal detector can help. A repairable cavity wall tie made for expansion by mechanical means should be avoided because with no care and a lot of hole holes that are not drilled that could eventually be drilled near the bed joint (where post-torsion expansion could cause damage to the fix (see below) and render the wall tie ineffective and is a waste of time as well as money. Mechanical expansion ties function by generating an expansive force that extends upwards, through the stone or brick; much like a rawlbolt. If the material is unable to take these strains, it fails and the fixing is affected. So, most manufacturers of wall ties advise that fixing the wall ties at the ‘centre of brick’ or the centre of brick, which is difficult to do when the brick is hidden beneath render (not to mention the internal leaf, which is always hidden).

In the event that render exists, only non-expansive wall ties are recommended for example: resin-bonded wall ties with both skins Helifix ResiTie, or resin and friction fix, like that of Helifix RetroTie (friction fix in the inner leaf that is able to be tested independently of the outer leaf) which is followed by the resin fixation in the outer leaf.

The primary material used for wall ties used for remedial purposes are made of stainless steel. This means that , in the real world, they shouldn’t be corroding. But there are situations where more precautions are required, and a superior quality stainless steel 316 grade commonly called’marine grade’, is recommended. This is the case for coastal areas, areas with contaminated sand, as well as on certain prestige or historical buildings in which a long-lasting life is required (we have installed Cintec the 316-grade stitching anchors into York City walls, after the 500 year life span was stipulated). The higher grade stainless is employed in a few wall ties with helical friction fix especially those that fix in one step that goes via the outside skin, and into the leaf’s inner. But I don’t specify the wall ties because of the possibility of failure of the leaf fix, which can’t be tested randomly.

Testing? This is vital for any remedial wall tie installation. The process is generally simple tension tests to ensure that the wall ties are firmly gripping the masonry enough to meet the specifications of design. The new wall ties put in by a bricklayer, are not required to be tested. They are easy to install on an open bed-joint. What could be wrong? Installation of the wall tie in a remedial manner is distinct. There are many things to be avoided. Even if you take your time selecting the right hanging tie for your wall, these can don’t provide the solution. This is the case for all of the wall ties that are available from experts or on the internet. My suggestion is that if wall tie is not tested, avoid using them. The reason is that homes vary the bricklayers, bricklayers are different mortar mixes differ as well as the overall quality of the walls are dependent on the mortar mix. The inner leaf may be soft blockwork or the rock-hard engineering brick. Each of the remedial wall ties has flaws and there isn’t one that can be used in every situation. Only by testing on the spot will anyone be able to identify one house in which the ties do not conform to exactly what was stated on the box’.

A tension testing rig is approximately PS700 plus VAT. Since every job requires testing, the wall tie expert could have several and have one on every contract. Furthermore they are carried from vans, as well as on windy scaffolds , they can be damaged and lose their accuracy. Because of this, they need to be calibrated every each year and could cost more than PS100 every time. Only those who use them weekly will be able to justify the expense. While they can get hired out, usage of them requires an understanding and some knowledge. An extensive selection of adapters to work with the broad range of wall ties for remedial use that are available is essential too… it’s not worth using a rig if discover you’re wall ties that you’re using aren’t compatible with it. Testing can vary in its intensity, ranging from a simple 5percent of the ties up to the fullest extent of 100% in extremely delicate situations or with unique masonry specifics. Testing is useless without an acceptable pass or fail number. It can range from 1Kn up to more, based on the test.

Be aware of the reasons tests are performed. It’s about getting a perfect job, and also gaining credibility of the wall tie. It is essential to have a reliable system for recording gauge readings. It should be recorded, but could also be complemented with photographs of measurement readings and test locations. I’ve been adding this method to our procedure for the past 16 years, and it’s becoming popular with different wall tie professionals.

What happens if tests show an error? In a way this is a blessing because you’ve learned the things you didn’t know otherwise , and you are able to take the necessary steps to correct the issue. If the tests for tension are a little off target, it is possible to look into the way to install it; perhaps you should drill a larger hole? If that’s not feasible what about a slight increase in the density of wall tie? In the opposite, it could be that the wall tie isn’t suitable for the wall being tested What alternatives are there? Could they be tested with and a change in specification that is authorised? These are the kinds of decisions that certified wall tie installers as well as experts must take, and having trained, properly briefed and certified personnel will consider this. If a specialist contractor involved, it is important to have the support of the management team; putting procedures in place that can handle or anticipate, these issues will ensure that the job is up to the task. This is the main reason City and Guilds designed a level 2 National Vocational Qualification for wall tie technicians. I’m very proud of saying that my technicians and I have.

After the job is completed, A guarantee is nice? Of course, if the contractor or DIY project was completed it isn’t an alternative. Most of the time, these jobs are backed by a warranty usually up to 20 years. It should be considered only a last resort to cover failure, and even if the work was completed in accordance with the guidelines laid in the previous paragraph, does it truly necessary?

The answer is yes. The reason for this is not to allow it to be defended. The reason is so that the problem of corrosion in wall tie can be put aside and put aside. Homes are bought and sold and mortgages are renewed with other lenders and loans are issued against property due to a variety of reasons. A solid insurance-backed assurance means the transactions can be completed without the risk of corrosion to the wall tie being added to the mix. The fact that you have the paperwork on hand, including the insurance policy, and other strengthens the reliability of the wall tie installation and prevents unnecessary surveys and disputes in the future.

A company can’t last forever, therefore the need for real insurance backing for guarantees is essential. Guarantee protection insurance is available through all reputable specialist contractors and is an absolute necessity for me.

Here’s a quick overview of the cavity wall tie replacement process from a practical point of view. I hope you find this guide useful