Cavity Wall Ties - Uses, Selection and Identifying Failure

What are wall ties?

Wall ties, which are often referred to as brick ties, are used in buildings with cavity walls to connect the internal and external leaf walls allowing the two leaves to work in synchronization with each other. Although they are hidden from sight after construction, wall ties play a pivotal role in the buildings stability.

Severe structural issues can arise from the improper or insufficient use of wall ties such as dampness, masonry cracks and in severe cases, even the collapse of the outer leaf wall. At My Trade Products we stock the tried and trusted Ancon brand who are global leaders in connecting, fixing, lifting and anchoring technology for the construction industry since 1882.

Wall ties these days are generally made from stainless steel as it can withstand corrosion caused by moisture and cement without needing any additional layer protection. The Ancon wall ties offer a maintenance-free life and are specially engineered to keep material content to a minimum. Some composite materials are also used, such as Ancon’s Teplo range of ties which are made from pultruded basalt fibres set in a resin matrix, which are ideal in ultra-low energy construction where the prevention of heat loss via ‘thermal bridging’ is particularly important.

Installing Wall Ties

In normal brick to block construction the wall ties are built into the inner and outer leaves. The wall ties should be pressed down in, and then surrounded by fresh mortar. Please note, wall ties should never be pushed into a pre-built joint. When installing, a slight grade should be applied to allow moisture to cross the cavity towards the outer leaf. The drip part of the tie should point downwards and positioned near the centre of the open cavity.

If building a different type of cavity wall such as thin-joint blockwork or timber/steel frames then the wall ties will normally be installed after the inner leaf has been constructed and during the construction of the outer masonry leaf.

Which size wall tie to use?

Wall ties need to be long enough to cross the cavity and provide 62-75mm embedment in the mortar on either side. The following table summarises which size wall tie to use with different cavity width's

Nominal cavity width mm (Note 1)	Tie length mm (Note 2)	BS EN 845-1 tie
50 to 75	200	Type 1, 2, 3 and 4 to BSI PD 6697:2010 and selected on the basis of the design loading and design cavity width
76 to 100	225
101 to 125	250
126 to 150	275
151 to 175	300
176 to 300	(Note 3)

Notes:

1. Where face insulated blocks are used the cavity width should be measured from the face of the masonry unit.
   The embedment depth of the tie should not be less than 50mm in both leaves.
   3. For cavities wider than 175mm calculate the length as the nominal cavity width plus 125mm and select the nearest
   stock length. For wall ties requiring embedment depths in excess of 50mm, increase the calculated tie length accordingly.

 

Symmetrical Ancon wall ties (Types HRT4, RT2, ST1 and Teplo-BF) accommodate some site tolerance in their length, for both cavity width variation and centring of the tie. In line with PD6697:2010 and Approved Document A, the minimum wall tie embedment is 50mm. Longer wall ties will be required where cavities are outside the tolerance offered.

 

What spacing and positioning should you use for wall ties?

If both leaves of the cavity wall are 90mm or thicker then it’s recommended to use 2.5 wall ties per m² using a maximum horizontal spacing of 900mm and maximum vertical spacing of 450mm. Always check with the Building Regulations however as this may be varied in some instances. Distribute the wall ties evenly across the wall area in a staggered pattern except around openings such as windows, doors, roof verges, unreturned/unbonded edges and un-tied 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 result in a wall tie on every course of blockwork within 225mm of openings. Spacing may however be relaxed if the joint has a deboned tie spanning it. 

 

Which wall tie type should you use?

• Masonry to Masonry

There are many factors to take into account for selecting the right wall tie for the job such as the type of masonry, cavity width, number of courses/height of building and the geographical location.

All factors governing the correct use of wall ties in any given situation are covered by several Eurocodes and Building Regulations, which should be referred and adhered to. To complement the Building Regulations and Eurocodes, in the UK Ancon have an additional Published Document (PD 6697:2010) which aids in the selection of wall ties based upon geographic and topographic factors. This means that, in the majority of cases, cavity wall ties may be specified without the involvement of a structural engineer.

For Masonry to Masonry applications there are 4 types of wall tie to choose from:

Type	Application	Density	Maximum Building Height	Geographical Location
Type 1 e.g. ST1, SD1, Teplo-BF1	Heavy duty tie suitable for most building sizes and types. Not very flexible and not recommended for applications where there is expected to be excessive differential movement between leaves	2.5 ties/m² 3-4 ties/m² at unbonded edges	Any height	Suitable for most sites. However, for relatively tall or unusually shaped buildings in vulnerable areas, the tie provision should be calculated
Type 2 e.g. RT2, Teplo-BF2	General purpose tie for domestic and small commercial buildings.	As Type 1	15m	Suitable for flat sites where the basic wind speed is up to 31m/s and altitude is not more than 150m above sea level
Type 2 ties are suitable for use outside the parameters stated e.g. sites over 150m above sea level, buildings exceeding 15 metres etc, if shown to be adequate by calculation. Contact Ancon for more information.
Type 3 e.g. RD3, Teplo-BF3	Basic wall tie generally as Type 2 above	As Type 1	15m	Suitable for flat sites where the basic wind speed is up to 27m/s and altitude is not more than 150m above sea level
Type 4 e.g. HRT4, Teplo-BF4	Light duty wall tie suitable for box-form domestic dwellings with leaves of similar thickness	As Type 1	10m	Suitable for flat sites in towns and cities where the basic wind speed does not exceed 27m/s and altitude is not more than 150m above sea level

 

• Masonry to Timber frame ties

Timber frame ties are designed to allow for vertical movement caused by the shrinking and expanding of materials with different thermal expansion properties. The wall tie needs to be flexible enough to cope with the difference in movement and hence it is important to select the correct tie to suit the movement expected in the building. Ancon ties STF6 and TIM6 allow for 24mm of frame shrinkage and are suitable for most timber framed buildings up to 4 storey’s high. The Ancon TFMT7 is specifically designed to allow for greater movement of up to 65mm and therefore suitable for larger buildings.

Type	Application	Density	Maximum Building Height	Geographical Location
Type 5 e.g. Teplo-L-5	Timber frame tie suitable for domestic houses and industrial/ commercial developments of up to three storeys	4.4 ties/m² 3-4 ties/m² at unbonded	15m	Suitable for flat sites in towns and cities where the basic wind speed does not exceed 25m/s and altitude is not more
Type 6 e.g. STF6, TIM6, Teplo-L-6	As Type 5 but suitable for developments of up to four storeys	As Type 5	15m	Suitable for flat sites in towns and cities where the basic wind speed does not exceed 25m/s and altitude is not more than 150m above sea level
Type 7 e.g. TFMT7, Teplo-L-7	As Type 5 but suitable for developments of between five and seven storeys, being designed to accommodate the increased vertical	Calculated for actual performance required for each site location	18m	Calculated for actual performance required for each site location

 

Identifying Wall Tie Failure

It can be tricky to identify exactly when a wall tie has failed and the extent of the failure but the most common sign is regular horizontal cracks appearing in the outer wall. As the wall tie rusts it can expand causing the mortar to crack and therefore allowing water to seep in. Sometimes this rust can build up causing expansion which in turn can mis-shape the wall by bulging or bowing

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

If the lintels around doors and windows look like they've sagged or lifted this may also be a sign.

If it's suspected that you have a wall tie failure, professional help from a surveyor should be sought. They have specialist equipment and detectors to determine the extent of the deuteriation of the wall tie.

 

My Trade Products

Shop our range of Ancon wall ties and retaining clips here and, as always at My Trade Products, if you require larger quantities than we are showing in stock or any of the wall ties mentioned that aren’t available on our site please get in touch sales@mytradeproducts.com 

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