Repairs: walls

Wall tie failure is a common problem on many older properties – visibly apparent from the horizontal mortar joint cracks at wall tie bedding intervals.

Cast iron or steel bars were commonly employed to brace the leaves of cavity construction, though not exclusively so, and there are many other types of wall tie that have been in use over the last century or more. For example, cranked, ceramic glazed ties are prone to lack of mortar adhesion, particularly where lime mortars have been used and where the glazed surface of the tie might cause very poor bonding.

Iron ties, if they were ever galvanised, have a finite lifespan. (Some were dipped in bitumen, some galvanised, others not at all.) As they deteriorate, the iron ties are prone to delaminate, causing a significant expansion within the bedding joint of the wall and a tell-tale pattern of horizontal cracks at about 450mm (18 inch) centres appears.

This usually manifests itself first around door and window openings where the pressure and loading around the tie is less.

However, a pattern is not always visible. Occasionally you may come across a substandard house with perhaps only one tie on one wall! Although this defies the laws of physics to some extent, it is surprising how many buildings have stood the test of time with only minimal bracing of this kind.

Although building age is a reasonable indicator of when cavity wall ties might have been employed, in some parts of the country they were used much earlier than in others. For example, in parts of the south coast, wall ties were commonly used in buildings dating from about 1870, whereas they only became common in parts of London or north Surrey from the 1920s.

The case of the waving wall Using a metal detector to locate the old wall ties is useful, but does not guarantee results. About 20 years ago, the author inspected an old hotel on the south coast, where ceramic wall ties had been used and so of course a metal detector was of limited value. The wall was a substantial one, and the external face of the wall had pulled away from the wall ties under wind suction. The ceramic wall ties had then dropped down within the cavity, and when the wind suction dropped, the wall could no longer return to its original position because it was blocked by the wall ties. The wall was actually rippling under the wind load. A rebuilding operation ensued, requiring substantial scaffolding (and cleaning and reuse of the bricks on what was a listed building). The expense was considerable. A preventative maintenance programme might have picked up this detail, so that remedial wall ties could have been fitted before the defect progressed to this costly state of affairs.

Solution

Wall ties are probably one of the easier repairs to implement. There are various proprietary systems on the market including an expanding rawl-bolt pattern, and a stainless steel helical bar that is driven into the centre of the brick, cutting a thread and self-tapping into the masonry as it is inserted.

Crudely repaired using mastic – an expansion 'joint' has 'developed' on a long factory wall, where none was allowed for in the construction!

Most of these systems use an injected polyester resin to provide additional adhesion into the internal skin brick, and particularly on the external brick skin where the act of inserting the tie is likely to have reamed-out the insertion hole, providing a less tight fit unless some form of glue is applied.

Before proceeding check:

• Is it a cavity wall? – Sometimes a solid wall with a stretcher bond can be mistaken for a cavity wall (an old 13-inch wall, for example). If there is no door or window reveal to check wall thickness, carefully probe the wall.
• The condition of the mortar jointing to the wall – Occasionally the mortar bond will have desiccated so far that, even if the wall ties are repaired, the condition of the bonding and adhesion in the mortar is so poor that it may be easier to reconstruct the external skin of the wall (commonly seen in ancient lime mortars).
• Which leaf of the cavity wall is load-bearing? – Although good building practice and long-established tradition suggests that the inner leaf should always be load-bearing, on some older properties the roof and wall plate may bear down on the external leaf. A quick check beforehand will establish if any additional means of support are required before laying into the external leaf of the wall and potentially removing the support.

Another option: On a 13 inch solid wall, often the facing brick bulges away from the 215mm (9 inch) wall beneath. If not too severe, the face brickwork can be pinned back using the helical remedial tie system mentioned above. There is a grout offered as part of this proprietary system to assist with bonding back together.

Note:

• Usual practice is to install the new remedial wall ties first before then isolating the old wall ties to reduce attrition to what may be a very tired wall bond.
• Isolation can sometimes be done by using a needle gun to expose the end of the tie before coating it in polyurethane foam to insulate it from moisture and prevent any excessive further rusting. But it would be preferable to completely isolate the end of the tie from the outside wall and prevent further expansion and pressure on the brickwork (which, if allowed to continue unchecked, can cause a pattern of rippling and bulging to the wall and eventually might lead to collapse, although few properties ever reach that stage of deterioration).
• When the masonry panel has been re-secured using the new ties, it is then safer and easier to remove bricks adjacent to each rusting and defective wall tie, and bend the defective tie end down within the cavity. It is then no longer bedded into the masonry, where it might continue to rust, expand and distort the wall.

Cost sequence - wall ties

• Specification based on a single elevation wall: 10m in length and 2 storeys high, with gable, and with 3 window openings and 1 door opening.
• Assumes owner/occupier supplies power.
• Assumes all areas are accessible with no special access required, e.g. to bridge-over conservatories, outbuildings or other projections which could make working dangerous or add significantly to access costs.
• Use of helical tie is assumed in this instance.
• Contractor to supply access, e.g. scaffold tower, to enable safe working access to upper limits of wall.

1. Install new helical wall ties by drilling to centre of brick at 450mm vertical centres and 900mm horizontal centres with double density ties to reveals around door and window openings, and all works in accordance with British Standards, including wall tie densities.
2. Ensure ties are soundly bonded by self-tapping, and use of resin fixing to both inner and outer skins of walls.
3. When all new ties are stabilised and fixed, allow for careful break out of individual bricks to enable old, defective and rusting ties to be removed/isolated by bending down from the outer leaf within the cavity of the wall. Wall ties to remain fixed to inner leaf.
4. Re-insert and point-in brick where defective wall ties have been removed. Allow for 100% breakages and matching in of new brick to existing - assumes a common brick stock such as a London red brick or similar.
5. Allow for removal of bricks above damp-proof course level at 1.5m centres and raking out using bent pipe or similar to remove any slovens or debris which may have dropped to the bottom of the cavity, to clear the cavity and ensure damp-proof course operates effectively.
6. Reinstate where brick is removed. Assumes 100% breakages to all brick openings. Allow for matching basic specification brick as detailed above.
7. On completion of all works, clear away all scaffold abd debris and arisings.
8. Allow for repointing only in areas where new bricks have been inserted with no repointing to the main wall area.
9. Allow for coloured mortar mix to repoint the face of the brick where new wall ties have been drilled through.

Wall ties - COST £3,500

Small works pricing

Since the original price estimating in 2008 the economic turmoil of the last few years has caused some disparities in pricing - if you are reviewing these figures in the London area they may look laughable - if you are located in Hull they might still look a bit expensive. Please treat them with caution and of course always consider obtaining more than one quote against which to test prices. Reference to the BCIS or a small works pricing book such as Spons or Laxton's will help assess costs and the hourly labour rates upon which they are based.