How do I tell tie failure from subsidence?

The pattern. Wall tie failure gives horizontal cracks along the bed joints at regular vertical intervals, following the tie grid, often with a visible bow. Subsidence gives diagonal cracks that taper, are wider at one end, and step through the brickwork. They are different faults with different repairs.

Can new ties be fitted without rebuilding the wall?

Usually yes. Remedial ties are drilled and fixed through both leaves from outside, so the wall stays up and the inside is undisturbed. Rebuilding is needed only where the outer leaf has bowed too far to be restrained safely.

Why do the cracks appear every few courses?

Because that is where the ties are. With ties bedded at roughly 450mm vertical centres, a corroding tie expands the joint it sits in, and the cracking repeats on the same grid — about every sixth or seventh course of brickwork.

Will repointing the cracks fix it?

No. The steel behind the joint keeps corroding and keeps expanding, so pointed cracks reopen. Worse, it removes the evidence a surveyor needs to identify the fault, and the leaf carries on losing restraint out of sight.

High risk

Updated 30 August 2026

Bulging Brickwork And Wall Tie Failure

The outer leaf of a cavity wall has bowed outwards, often with regular horizontal cracks along the mortar beds.

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What's happening?

A cavity wall is two thin leaves working as one, and what makes them act together is the wall ties bridging the gap. Approved Document A expects those ties at 900mm horizontally and 450mm vertically, or at least 2.5 ties per square metre, with extra ties no more than 300mm apart vertically within 225mm of every opening, movement joint and roof verge. Older galvanised steel ties corrode, and rust occupies more volume than the steel it came from, so a corroding tie jacks the bed joint it sits in apart. Because the ties are laid on a grid, the cracking follows that grid — horizontal cracks at regular vertical intervals, roughly every sixth or seventh course. That regular spacing is the giveaway, and it is what separates tie failure from settlement or subsidence.

What usually causes it?

Corroding galvanised steel wall ties expanding in the bed joints and lifting the outer leaf
Ties omitted, too few, or missed entirely around openings and at verges when the wall was built
Ties bridged by mortar droppings or badly installed insulation, keeping them permanently wet so they corrode faster
Loss of restraint where the outer leaf is no longer tied back to a floor or roof, so it bows under wind load
Cavity fill or debris packing the cavity and pushing the leaves apart
Sulphate attack in permanently damp brickwork expanding the mortar and the wall with it
An earlier repair that pointed over the cracks without replacing the ties, so the movement carried on hidden

Is it dangerous?

Yes, and this is not a wait-and-see fault. An untied outer leaf is a thin, tall panel of masonry with nothing holding it back, and its failure mode is falling outwards in a strong wind rather than crumbling slowly. Treat it as urgent where the bulge is pronounced, where the wall is a gable or above a door or a pavement, where cracks are opening, or where the leaf sounds hollow when tapped. Lenders and surveyors flag wall tie failure for the same reason. Do not stand or work beneath a bulging leaf, and do not let anyone lean a ladder against it — the load path it was built for no longer exists.

Can I fix it myself?

No. This is a structural repair on a wall that may already be unstable, and the diagnosis alone needs a borescope through drilled holes or a metal detector to find where the ties actually are and what state they are in. What you can do is document it: photograph the elevation from a distance to show the bow against a straight line, mark the crack ends with a dated pencil line, and measure them again in a month. Never fill or point the cracks first — filler hides the pattern that identifies the fault, and the corrosion behind it carries on regardless.

When should you call a bricklayer?

Call a bricklayer or a structural engineer now if you can see a bulge, or horizontal cracking at regular intervals up a wall. Call urgently if the bulge is on a gable, above an entrance or over a pavement, if it has grown, or after high winds. If a survey has flagged wall tie failure ahead of a sale, get the ties inspected properly rather than repointing the cracks, because a cosmetic repair does not stop the corrosion.

What will the bricklayer actually do?

Survey the cavity with a borescope and metal detector to map tie positions, tie type and the extent of corrosion
Confirm the fault is tie failure rather than settlement, lintel deflection or loss of restraint
Install replacement stainless or helical remedial ties on a designed grid, including extra ties around openings and verges
Isolate or remove the failed ties so the corrosion cannot keep expanding the joints
Rebuild sections of the outer leaf where the bow is too great to be pulled back or tied through
Repoint and make good only once the wall is restrained, and clear cavity debris that kept the ties wet

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Leaning Garden WallHigh risk Rain Coming Through A Solid Brick WallCaution Cracks In WallsCaution Signs Of SubsidenceHigh risk

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