Adhesive failure often initiates at corners and sharp edges because these points act as stress concentrators. Any mechanical load, thermal movement, or shrinkage force applied to the repair focuses intensely at these narrow boundaries, causing the bond to quickly fatigue and peel off (delaminate) from the metal substrate.

Here are genuine solutions focused on geometry and technique to mitigate edge stress and prevent peeling.

1. Geometric Stress Management (Filleting)

The most effective solution is to eliminate the sharp edge that concentrates the stress, distributing the load over a larger area.

• Create a Radius (Fillet): The most crucial step is to never leave a sharp, 90∘ angle where the putty meets the metal. Instead, shape the putty with a smooth, concave curve called a radius or fillet . This smooth transition distributes the mechanical load and internal stress over a significantly larger area, preventing the stress from peaking at one vulnerable point.
• Feathering the Perimeter: Beyond the fillet, the perimeter of the repair should be gradually tapered or feathereddown to a very thin edge that blends into the surrounding metal. A thin, feathered edge is much more resilient to peeling forces and fatigue than an abrupt, thick edge.
• Avoid Over-Tightening near Edges: When reassembling components, be acutely aware of over-tightening boltsnear the repair area. Excessive torque can introduce high, localized tensile stress that immediately concentrates at the sharpest corners of the putty, leading to micro-fractures that initiate peeling.

2. Preparation for Edge Anchor

The bond at the edge needs to be strong enough to withstand the peeling forces it will encounter.

• Extend Abrasion Beyond the Edge: Ensure the abrasion (surface roughening) extends significantly beyond the area that the putty will cover. When you apply the putty, it should bond to the rough surface well past the sharp corner where the forces are greatest.
• Subtle Undercutting: For defects that run to a corner, prepare the corner so that the inner metal is slightly undercut or chamfered inward. As the putty cures and potentially shrinks, the geometry forces the material to pull into the corner rather than away from it, creating a robust mechanical lock that actively resists the peeling motion.
• Deep Mechanical Keying: When preparing a defect (like a crack or pit), ensure the V-groove or chamfer runs right up to and, ideally, slightly around the corner. This anchors the putty structurally, making it much harder for a small surface peel to propagate into a full bond failure.

3. Application Technique (Wetting Out)

A flawless bond at the edge is necessary to prevent the peel from starting in the first place.

• Vigorous Edge Scrubbing: When applying the putty, use a stiff tool (spatula or spreader) to vigorously scrub and smear a small amount of putty right into the corner and along the entire edge perimeter first. This action ensures the putty thoroughly wets out the prepared surface and penetrates every microscopic anchor point, achieving 100%surface contact where the stress will be highest.
• Consolidation: Apply sufficient force to the putty as it’s placed to consolidate the material. Air voids near the surface, especially at corners, become weak points that act as initiators for crack formation under cyclic load.