Wall ties explained, and why they fail

In a cavity or veneer wall, the two parts are held together by small metal ties buried in the mortar. You never see them, but they are doing quiet structural work, and when they corrode it becomes a problem.

What wall ties do

A wall tie is a strip or wire of metal built into the mortar bed, bridging the gap between the outer brick skin and the inner skin or frame. They stop the outer skin bowing, leaning or pulling away in the wind.

A good tie also keeps water from tracking across the cavity. It is shaped with a kink or drip in the middle so any moisture that lands on it drips down into the cavity instead of running inside.

Why ties fail

Most tie problems come down to corrosion and bad installation:

• Old galvanised or black steel ties rust over decades, especially in damp walls. As steel rusts it swells, which can actually push mortar joints apart.
• Mortar or debris dropped on a tie during building lets it bridge water across the cavity.
• Too few ties, or ties laid sloping the wrong way, so water runs inward.

Signs of trouble

Tie failure shows up slowly. Watch for:

• Horizontal cracks in the mortar at regular spacing up the wall, often around every fifth or sixth course where the ties sit.
• An outer skin that bulges or leans away from the house.
• Rust stains weeping out of the joints.

In older Melbourne homes, particularly anything with original steel ties, this is worth taking seriously. A leaning brick skin does not fix itself.

What can be done

The good news is you usually do not have to rebuild the wall. Replacement ties can be drilled and fixed in through the existing brick to re-anchor the skin, and corroded sections sorted before they get worse. The trick is catching it while it is still cracks and not a bulge.

If you have noticed stepped or horizontal cracking or a wall that looks like it is leaning, send a photo and your suburb and we will tell you whether it is the ties or something else.