Collection: Bi-Component Epoxy Glue

A two-part epoxy adhesive combines a resin and a hardener mixed at the point of use. Unlike an adhesive that sets by evaporation, it cures through a chemical reaction: it therefore hardens in thickness, in confined spaces, and without shrinkage. That is what makes it the reference adhesive for structural metal bonding, wherever the joint has to carry a load.

What is in this range

• 3M Scotch-Weld DP100, two-part structural epoxy.
• 3M Scotch-Weld DP125, flexible-cure epoxy.
• 3M Scotch-Weld DP460, high-strength structural epoxy.

See also our industrial adhesives and our adhesive sealants.

Choosing between two epoxies

Four criteria settle it nearly every time, and all four are on the data sheet.

1. Work life. The window during which the mix stays fluid enough to spread and the parts can still be repositioned. A five-minute epoxy means the assembly must be ready before you mix; a forty-five minute epoxy leaves time to align several parts.
2. Mix ratio. It is not a guideline. Excess hardener does not cure faster, it leaves unreacted molecules in the joint and lowers final strength. Two-part cartridges with a static mixing nozzle remove the risk.
3. Flexibility. A rigid epoxy gives the highest shear strength but copes badly with impact and vibration. A flexible epoxy such as DP125 gives up a little pure strength and gains a great deal in peel and fatigue resistance.
4. Gap fill. A filled epoxy holds a thick bond line without slumping; a fluid grade is made for closely fitted parts.

Surface preparation decides the outcome

When a bonded assembly fails, the break almost always happens at the interface between adhesive and metal, not within the adhesive. In other words the preparation failed, not the product.

Three steps, in order. Degrease first, with clean solvent and a single-use wipe. Abrade next, to increase the real contact area and break the surface oxide layer. Degrease again, because abrading brings back particles and traces of grease.

One point deserves attention on aluminium: the oxide layer reforms within minutes in open air. The sooner bonding follows preparation, the better the strength.

Epoxy, polyurethane or structural acrylic

Epoxy gives the best mechanical strength and the best temperature resistance, at the cost of a long cure and demanding preparation.

Structural acrylic builds strength in minutes and tolerates less well prepared surfaces, sometimes even slightly oily ones, but its odour is strong.

Polyurethane stays flexible and absorbs movement, which suits large assemblies subject to thermal expansion rather than concentrated load bearing.