What spacing and positioning should you use for cavity wall ties?

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What do you mean by wall ties?

Wall ties, commonly referred to as brick ties, are utilized for buildings with cavity walls to connect the exterior and internal leaf walls, allowing the two leaf to work in synchronization to each other. Although they’re out of the view of construction workers, wall ties play a important role in building stability.

A number of structural issues could arise due to insufficient or inadequate use of wall ties , such as cracks in masonry, dampness and in severe cases, even the collapse of the outer leaf wall. We at My Trade Products we stock the trusted and tested Ancon brand who are global leading in connecting, fixing, lifting and anchoring techniques for the construction industry since 1882.

Cavity wall ties these days are mostly made of stainless steel, as it is able to stand up to the effects of moisture and cement without the need for additional protection layer. The Ancon wall ties provide the longest life without maintenance and are specifically designed to limit the amount of material used to an absolute minimum. A variety of composite materials are used, like Ancon’s Teplo range of ties, which consist of pultruded basalt fibres , set in an epoxy matrix. These are ideal in ultra-low energy construction, where preventing heat loss via ‘thermal bridging is crucial.

Installing Wall Ties

In typical brick-to-block construction, wall ties are placed between the inner and outer leaves. The wall ties should be pressed down in an area, then covered by fresh mortar. It is important to note that wall ties should never be placed in a pre-built joint. If installing, the slightest slope must be applied to allow moisture to flow through the cavity and towards the leaf’s outer edge. The drip portion of the tie should be pointing downwards and be placed near the middle of the open cavity.

If you’re building an alternative type of cavity wall like blocks with thin joints or timber/steel frame then wall ties will usually be installed after the inner leaf is constructed as well as during the building of the outer masonry leaf.

What spacing and how much space should you use for wall tie?

If both of the leaves that make up the cavity wall measure greater than 90mm then it is recommended to use 2.5 walls ties for each m2 with a maximum horizontal space of 900mm, and a maximum vertical spacing of 350mm. Always ensure that you are in compliance with the Building Regulations however as this could be different in certain situations. Distribute the wall ties evenly across the wall area in a staggered manner, except around openings such as doors, windows roof verges, roof edges, unreturned/unbonded edges, and untied vertical movement joints where the vertical spacing of the wall ties should be reduced to a maximum of 300mm and no more than 225mm from the edge of the opening. This may lead to the wall tie being placed on each blockwork course within 225mm from openings. The spacing can be permissible if the joint has a deboned tie across it.

What kind of tie is best?

Masonry to Masonry

There are many aspects to consider when picking the appropriate wall tie for the job like the type of masonry, cavity width as well as the number of courses/heights within the building and the geographical location.

Every aspect that influences the right installation of wall-tie ties in any given circumstance are covered under a range of Eurocodes in addition to the Building Regulations, which should be referred and adhered to. To supplement the Building Regulations and Eurocodes, Ancon in the UK Ancon have an additional published document (PD 6697:2010) which helps to select wall ties based upon topographic and geographical aspects. This means that most of the time cavities wall ties can be specified without the assistance of a structural engineer.

Masonry to Timber frame ties

The timber frame tie is designed to allow for vertical motion caused by expansion and shrinking of materials that have different thermo-expansion properties. The wall tie should be able to cope with the variations in motion and , therefore, it is vital to select the appropriate tie for the type of movements expected by the building. Ancon ties STF6 and TIM6 allow for 24mm frame shrinkage and fit well with most timber-framed structures up to 4 storey’s high. This Ancon TFMT7 is specifically designed to allow for greater movement of up to 65mm and therefore suitable for larger buildings.

Recognizing Wall Tie Failure

It isn’t always easy to determine the precise moment when a wall tie has failed and the extent of the failure but the most common evidence is normal horizontal cracks appearing in the wall’s outer. As the tie rusts, it will expand, causing the mortar to crack , allow water to get in. Sometimes this rust can build up causing expansion which may cause distortion to the wall, causing it to bow or bulge.

Another sign to look out for is cracks appearing in masonry of window reveals. As the rust builds up on the wall tie the force creates cracks in the window reveals which have particularly structurally vulnerable edges.

If the lintels around windows and doors look like they’ve been lifted or sagging, it could be a signal.

If you suspect you’re suffering from the wall tie is failing, professional help from a surveyor is recommended. They have specialist tools and detectors to assess the extent of destruction of your wall tie.