As the title of this guide suggests, this article addresses how to select the right type, length, spacing and quantity of replacement wall ties for a given project. For a complete insight to replacing wall ties in an existing building, please read our Professional Guide to Wall Tie Replacement.
Follow this link to see an animated illustration as to how to fix helical wall ties into an existing cavity wall.
There are two reasons why your building might need replacement wall ties.
In both cases, installation of a wall tie replacement system anchors the brick facade wall securely to the structural inner wall of the building, allowing the transfer and sharing of loads.
Provided that your walls are of a typical masonry cavity wall make-up, with each leaf being at least 90mm in thickness, you will need to install the remedial tying system at the rate of 2.5 wall ties per m2. Wall tie spacing should be at 900mm centres vertically by 450mm centres horizontally, in a staggered 'domino 5' pattern (PD 6697: 2010).
The areas of a wall most susceptible the effects of wind loads are the brick panels next to unbonded edges, such as those at gable apexes, vertical movement joints, and the sides of window openings. The installation of extra ties, at a rate of one fixing per 300mm height of brickwork, adds the necessary strength to these vulnerable areas.
In the unlikely event that either wall is less than 90mm thick, wall tie spacings should increase from 2.5 ties per square metre to 5 per m2 (450 x 450mm).
For wall tie replacement in brick-clad timber frame construction, the required spacing for retrofit wall tie installation is 4.4 wall ties per m2, the density increasing to 7 per square metre, where the basic wind speed exceeds 25m/s (BS 6399-2: 1997 Code of Practice for Wind Loads).
Why not use our Wall Tie Replacement Calculator to establish how many ties you will need.
Establishing the correct type of brick tie for your building will require a little DIY investigation. You should first check to see whether you have cavity wall insulation. If you have, you should avoid using chemically reactive resins and choose a stainless-steel wall tie system that uses the smallest installation bore to minimise any effect on thermal efficiencies. You will need to drill at least one investigation hole to each elevation and determine whether the bricks or blocks are solid (drilling rate will be constant) or whether they have perforations (drilling rate will be inconsistent).
Ascertain the cavity width (the gap between internal and external walls) by measuring the length of penetration of the drill bit when touching the surface of the inner (far) leaf and subtracting the thickness of the outer (near) wall. Refer to our Product Pages for your chosen wall tie replacement system to find out the length of the tie that you need for a given cavity span.
There are only minor differences between the installed costs of brick tying systems. The arrangement with the lowest material costs is usually the one where the installation process is the most time consuming and complicated. The wall tie system that appears to cost the most is typically the easiest and quickest to install, with the minimal prospect for operator error.
All our wall tie installation systems are relatively simple for a competent DIY enthusiast, a builder or a specialist contractor to install. However, we recommend that you select for use remedial wall ties that carry independent approvals for use in the building materials that make up your building structure.
See the video below to see the speed and simplicity of replacement wall tie installation using a Twistfix helical wall tie.
Where problems caused by wall tie corrosion involve more than installing a replacement cavity tie system, it is wise to seek professional advice.
Typically, you can leave in place any original wire-type or 'butterfly' wall ties, embedded in standard-sized mortar joints. Generally, the metal is of insufficient mass for any corrosion to cause structural damage to the walls. Merely installing a replacement wall tie system will restore stability.
Existing ties manufactured from steel plate, for example, vertical twist fishtail ties, have the prospect to significantly expand as they corrode, forcing the brickwork apart and creating a series of horizontal cracks in the mortar course housing the cavity-ties. If a wall shows horizontal cracks, spaced at 4-8 course intervals, the chances are that the existing tie-irons are, or have been, corroding. The build-up of iron oxide layers (rust) increases the mass of the tie and the force created splits the brickwork along the bed-joint from one tie position to the next. In such instances, it is wise to seek the advice of a Qualified Engineer to establish whether the corroding wall ties are fully expanded or are likely to enlarge further and cause additional distress to the wall. The Engineer will then consider the need for other actions; for example, the need to remove or structurally isolate the corroding wall ties from the brickwork.