Expanding bolts should not be used close to wall edges because the outward force they apply can crack bricks, mortar joints, or concrete, significantly weakening the fixing and reducing security.

How expanding bolts work

Expanding bolts secure a ground anchor by forcing the bolt outward against the surrounding material as it is tightened. This creates grip through friction inside the drilled hole. In solid, well-supported substrate with sufficient surrounding mass, this method is very effective.

However, the expansion force is transferred directly into the structure around the fixing point.

Why wall edges can be a problem

Near the edge of a wall or slab, there is less material available to resist the expansion force created by the bolt. If an expanding bolt is fitted too close to an edge:

• Bricks or blocks can crack
• Mortar joints can split
• Sections of wall can break away
• The fixing may loosen over time, even if it initially feels tight .

This risk is particularly high with:

• Brick walls
• Blockwork
• Thin or mediocre-quality concrete
• Walls with voids or air gaps

Minimum safe distances matter

As a general guideline, ground anchors using expanding bolts should not be installed within 2.0 metres (6 feet) of the top edge of a wall.

This means they should not be fitted to low garden walls or short retaining walls. The weight of masonry above the fixing point helps resist the expansion forces created when the bolts are tightened. Within 0.3 metres (1 foot) of the end of a wall or external corner.

Corners and wall ends are structurally weaker and more prone to cracking under expansion pressure. Ignoring these distances significantly increases the risk of structural failure.