Wall Tie Survey When Selling: Do You Need One?

Wall ties are one of those structural elements that most homeowners never think about — until they fail. These small metal connectors, buried within the cavity of your external walls, play a critical role in holding the building together. When they corrode and fail, the consequences can be serious: cracking, bulging walls, and potential structural instability that will concern buyers, surveyors, and mortgage lenders.

This guide explains everything sellers need to know about wall ties, from identifying whether your property is at risk to understanding what a specialist survey involves and how wall tie issues affect the sales process. For a broader overview, see our seller's guide to property surveys.

What are wall ties?

Wall ties are metal connectors that bridge the cavity between the inner and outer leaves of a cavity wall, holding them together as a single structural unit. Without wall ties, the two leaves of the wall would act independently, and the outer leaf (which is not load-bearing in most domestic construction) would be at risk of collapse.

Cavity wall construction became standard in the UK from the 1920s onwards, replacing the older solid wall construction. Almost all UK homes built since the 1930s have cavity walls with wall ties. The ties are typically spaced at 900mm horizontally and 450mm vertically (every sixth course of standard brickwork), with additional ties around openings such as windows and doors.

Why wall ties fail

The primary cause of wall tie failure is corrosion. Wall ties installed from the 1920s to the early 1980s were typically made from mild steel with little or no protective coating. Over decades, exposure to moisture within the cavity causes the steel to rust and weaken.

The corrosion process

As steel corrodes, it forms iron oxide (rust), which occupies a greater volume than the original steel — approximately six to ten times greater. This expansion exerts pressure on the surrounding mortar, causing the mortar joints to crack. The characteristic pattern of horizontal cracking at regular intervals is caused by the expanding corroded ties pushing the mortar apart at each tie location.

Factors that accelerate corrosion

• Exposure to moisture — properties in coastal areas, high-rainfall regions, or exposed hilltop locations experience faster corrosion because more moisture enters the cavity.
• Black ash mortar — some properties built in the 1920s to 1950s used mortar containing black ash (from coal combustion), which is highly corrosive to mild steel.
• Cavity wall insulation — retrofitted cavity insulation can bridge the cavity and transfer moisture directly to the ties, accelerating corrosion. It also makes ties more difficult to inspect.
• Chemical composition of ties — some wartime and post-war ties were made from lower-quality steel that corrodes faster.

Properties most at risk

Not all properties with cavity walls are equally at risk. The following factors increase the likelihood of wall tie problems.

Properties built after the mid-1980s typically have stainless steel or heavily galvanised ties that are far more resistant to corrosion and are unlikely to need attention for many decades. For broader guidance on issues common to properties of this era, see our guides on selling a 1960s house and selling a 1970s house.

Signs of wall tie failure

If you are selling a property built during the at-risk period, look for the following signs.

• Horizontal cracking — the most characteristic sign. Look for horizontal cracks in the mortar joints of the outer wall, occurring at regular intervals (typically every sixth course of bricks, approximately 450mm apart). The cracking pattern will be consistent across the wall.
• Bulging or bowing — the outer leaf may visibly bow outward, particularly at upper levels where the restraint from the inner leaf is reduced. This can be checked with a plumb line or by sighting along the wall face.
• Cracks around openings — cracking or distortion around windows and doors, where additional ties are (or should be) installed.
• Rust staining — brown staining on the wall face at tie positions, caused by corrosion products being washed out by rain.

It is important to note that horizontal cracking can have other causes (such as thermal movement, structural settlement, or sulphate attack on mortar), so a specialist survey is needed to confirm wall tie failure.

What a wall tie survey involves

A wall tie survey is a specialist inspection that assesses the condition of the ties within the cavity. The process has several stages.

Visual inspection

The surveyor examines all external walls for cracking patterns, bulging, rust staining, and other visible signs of tie failure. They also inspect internal walls where accessible, checking for cracking that may correspond to external findings.

Metal detection

Using a metal detector calibrated for wall ties, the surveyor scans the walls to locate the ties and determine their spacing pattern. This confirms how many ties are present and identifies any areas where ties may be missing or have been previously replaced.

Borescope (endoscope) inspection

The surveyor drills a small hole (typically 10mm diameter) through a mortar joint in the outer leaf and inserts a borescope — a thin, flexible camera — into the cavity. This allows them to see the condition of individual ties at close range, checking for corrosion, expansion, remaining cross-section, and whether the tie is still properly embedded in both leaves.

The surveyor will typically inspect ties at several locations around the property, focusing on areas showing the most severe cracking or those most exposed to moisture. The small inspection holes are filled and pointed after the survey.

Crack and movement measurement

If cracking or bulging is present, the surveyor measures crack widths and the degree of any outward movement using gauges and plumb lines or laser levels. This data helps assess the severity of the problem and the urgency of remedial action.

Wall tie replacement: how it works

If the survey confirms wall tie failure, replacement is the standard remedial approach. The process involves three key steps.

1. Installing new ties — new stainless steel ties are inserted through holes drilled in the outer leaf, through the cavity, and into the inner leaf. They are fixed in place either mechanically (expanding anchors) or with resin. The new ties are installed at the standard spacing pattern.
2. Isolating old ties — the corroded old ties are either physically removed (rare, as it is more disruptive) or isolated by cutting them back within the cavity so that any continuing expansion does not affect the mortar joints.
3. Making good — drill holes are filled and pointed, and any cracked mortar joints may be repointed. If significant bulging has occurred, the outer wall may need additional restraint or, in severe cases, partial rebuilding.

Costs

These costs include scaffolding, new ties, isolation of old ties, and making good. The work comes with a guarantee — typically 25 to 30 years — that transfers automatically to future owners. This guarantee is a valuable document for your sale. For guidance on whether to complete the work or adjust the price, see our guide on when to fix versus reduce the price after survey.

Impact on the buyer's mortgage

Wall tie failure is classified as a structural defect, and mortgage lenders treat it accordingly. If the buyer's surveyor or valuer identifies wall tie concerns, the lender may take one or more of the following actions.

• Require a specialist report — the lender may require a wall tie survey before proceeding with the mortgage offer.
• Require remedial work — if failure is confirmed, the lender may require replacement to be completed before releasing the mortgage advance.
• Impose a retention — the lender may release most of the mortgage but hold back a sum until the work is completed post-completion.
• Reduce the valuation — the lender may value the property lower to reflect the cost of remediation, affecting the buyer's loan-to-value ratio. See our guide on average price reductions after survey for typical benchmarks.

Having wall tie replacement completed before marketing — with a transferable guarantee — is the most effective way to avoid mortgage complications. If you prefer not to carry out the work, providing a specialist survey and repair quotes allows the buyer to present these to their lender. For information on how structural issues generally affect surveys, see our guide to common survey issues.

Should you get a wall tie survey before selling?

A wall tie survey is not necessary for every property. Consider getting one if:

• Your property was built between the 1920s and early 1980s with cavity wall construction.
• You can see horizontal cracking at regular intervals on external walls.
• The property is in an exposed or coastal location.
• A buyer's surveyor has raised concerns about wall ties in a previous or current transaction.
• Neighbouring properties have had wall tie replacement carried out.

If your property was built after the mid-1980s, has solid walls (no cavity), or shows no signs of horizontal cracking, a wall tie survey is unlikely to be needed. A pre-sale survey can help identify whether wall ties are a concern worth investigating further. If in doubt, discuss the matter with your estate agent or solicitor before commissioning a survey.

Frequently asked questions