Section C Superstructure
Wall Ties – Typical types
There are many types of wall ties available in a number of materials.
Requirements for wall ties are specified in Irish Standard EN (I.S. EN) 845: 2003 + A1: 2008 Specification for ancillary components for masonry – Part 1 2003: Ties, tension straps, hangers, and brackets.
The materials from which wall ties can be manufactured are outlined in Annex A of I.S. EN 845.
Key Construction Points
For Irish conditions, Austenitic stainless steel has been proven to be effective. Manufacturers are required to provide information about the wall ties including; material specification, dimensions, load capacity, and minimum thickness of mortar bed joint as specified in Table 1 of I.S. EN 845.
Also, the following information is required to be indelibly and clearly marked on the product, on its packaging, on the delivery note, on the invoice or on any accompanying documentation supplied with the product according to Section 7 of I.S. EN 845:
The date of issue of I.S. EN 845-1 2003 + A1: 2008 and the product number.
The identifying mark or name along with the registered address of either the manufacturer or an authorised representative of the manufacturer.
In order to identify the product, type and relate the product to its description and designation, provide a unique reference number, name and code.
Care should be taken during construction to ensure that:
Embedment of 50 mm is capable of being achieved by the wall ties in each leaf.
Wall ties should suit the insulation where cavity insulation batts are used and hold the insulation firmly in place. Manufacturers or suppliers usually have suitable ties available for their insulation.
Drip should point downward for all wall ties.
Wall ties should never be pushed into mortar after the blocks have been laid. Should always be installed as the work progresses.
Wall ties should never fall inwards (backfall).
Where party wall are cavity walls, double triangle wall ties are used. An example of when these are used is on changes in level or on sloping sites.
There should never me more than a 1 m difference between both leaves of a cavity wall during construction.
Diagram C22 - Typical wall tie layout
Table C10 - Appropriate spacing and distribution of wall ties
A number of problem areas in cavity wall construction associated with damp penetration across the cavity have been identified. The most common problems have been detailed below for clarity. PLEASE NOTE: Care should be taken to avoid these.
Build up of mortar in the cavity
Cavity laths or boards should to cover the cavity to keep the cavities clean as well as daily cleaning of wall ties. Provide temporary openings at the base of the wall to gather debris.
Diagram C23 - Keeping the cavity clean - board across the cavity
Diagram C24 - Keeping the cavity clean - cavity lath
Diagram C25 - Mortar filling too high in the cavity
Mortar within 150 mm of the DPC due to mortar droppings filling bottom of the cavity is not permitted. Cavity should be kept clear for between 150 mm and 225 mm below the DPC level.
Walls ties sloping across the cavity should be avoided as they can act as a bridge across the cavity.
Diagram C27 - Wall ties sloping across the cavity
Diagram C28 - Wall ties sloping inwards - bridge across cavity
Care should be taken when laying block courses of both leaves, to ensure the inner and outer leaves are not at different levels so as to avoid backfalls in ties that will create a bridge across the cavity.
The accumulation of mortar droppings on wall ties should be avoided as it can allow the penetration of dampness from the external leaf to the internal leaf. Use cavity laths or boards along with daily cleaning of wall ties to ensure cavities and wall ties remain clean at all times.
Diagram C29 - Mortar droppings on wall ties - penetration of damp
Diagram C30 - Mortar build up on trays/lintels
Diagram C31 - Mortar build up on joists
If joists, purlins, projections, or similar protrude into the cavity, mortar build-up may occur. It is important to avoid such projections.
Timber ends must be treated with a preservative, a coloured preservative should be used.
Insulation that is not fixed correctly to the inner leaf is a big problem as it can allow a build up of mortar within the cavity. Wall ties appropriate for the insulation being used should be installed as per the manufacturer’s instructions.
Diagram C32 - Insufficient restraint of insulation against inner leaf
NOTE: Vigilance and care throughout the job will result in all these recurring faults being avoided.
Where stone cladding is to be provided along the external wall it is important to ensure that moisture is not passed to the internal leaf. In order to prevent moisture penetration through the wall, stone cladding must never be fixed directly to single leaf solid or hollow blockwork construction.
Diagram C33 - Stone cladding fixed directly to hollow blockwork - not permitted
Correct cladding fixing
Appropriate wall ties must be used when fixing stone cladding to the external wall, for example, stainless steel wall ties. Cladding may only be fixed to the external leaf of a cavity wall. The following requirements must be met for ensure adequate fixing of the cladding:
2.5 ties are required, at a minimum, per square metre.
Wall ties should have a maximum horizontal spacing is 900 mm and maximum vertical spacing is 450 mm.
Around opes, vertical spacing is reduced to a maximum of 225 mm.
Expanded metal strips are not suitable for use as wall ties.
Diagram C34 - Rising wall with stone cladding built off it
Diagram C35 - Correct fixing detail for stone cladding to the external leaf of a cavity wall