Metal is one of the trickiest substrates to bond well. It's rigid, it often carries an oxide layer or residual oil, and many metal joints in New Zealand end up outdoors, exposed to UV, salt air, or constant vibration from machinery or vehicles. Pick the wrong adhesive, and you'll get a joint that looks fine on day one and fails within months, sometimes without any obvious warning sign until the load finally finds the weak point.
The good news is that choosing the right metal bonding adhesive isn't complicated once you understand what the adhesive has to cope with. That comes down to the specific metals involved, the load the joint will carry, the environment it'll live in, and how it will be applied. This guide walks through that decision step by step, from the chemistry itself through to surface prep and application technique.
Why Metal Is a Difficult Substrate to Bond
Before getting into which adhesive to choose, it helps to understand why metal causes more bonding problems than materials like timber or plastic.
Metal surfaces are typically low in porosity, which means there's nothing for an adhesive to mechanically key into the way it can with timber grain or an open-cell foam. Bond strength on metal relies almost entirely on the adhesive forming a chemical or molecular connection with the surface, which is why surface condition matters so much more here than it does with most other substrates.
Metal also expands and contracts with temperature more than many other materials, and it conducts heat and cold quickly. A joint that sits in direct sun on an Auckland summer afternoon and then cools overnight goes through more thermal cycling than most people realise, and that movement puts ongoing stress on a bond line. Add oxidation (rust on steel, an oxide layer on aluminium), oils or machining residue left over from fabrication, and sometimes protective coatings like galvanising or powder coat, and you've got a surface that needs to be properly understood before it's glued.
Start With the Metals You're Bonding
Not all metals behave the same way under adhesive, so the first decision is about the materials rather than the product. Work out exactly what you're sticking together before you choose anything.
Similar vs dissimilar metals. Bonding aluminium to aluminium is a different challenge to bonding aluminium to stainless steel. Where two dissimilar metals are in contact, galvanic corrosion can develop over time if moisture gets into the joint, gradually weakening the bond from the inside. An adhesive that fully seals the joint against moisture ingress reduces this risk considerably. That's one reason a flexible, weather-resistant chemistry such as an MS polymer is often preferred for outdoor metal-to-metal joints, even when raw bond strength isn't the primary concern.
Surface finish. Mill-finish aluminium, painted steel, and polished stainless all accept adhesive differently. Smooth, low-porosity metals like stainless steel benefit from light surface abrasion and a compatible primer before bonding. Without that step, even a good adhesive has very little to grip onto.
Coatings and galvanising. Galvanised steel has a zinc coating that can interfere with cure on some adhesive chemistries. Painted or powder-coated metal bonds to the coating rather than the base metal underneath, so the coating's own adhesion becomes the limiting factor. 3M Scotch-Weld DP 8810NS is a toughened two-part acrylic listed for metalworking and for bonding plastics, composites and powder coats to metal. It has a 10-minute work life and reaches around 7 MPa of overlap shear strength in about 21 minutes. It's worth checking the technical data sheet for the specific product rather than assuming any metal adhesive will work the same way across every finish.
If you're working across a mix of aluminium, brass, copper or mild steel, it's worth browsing adhesives by metal type rather than reaching for whatever's on the shelf, since different alloys have different bonding requirements.
Match the Adhesive Chemistry to the Job
There's no single best glue for metal-to-metal. The right choice depends on what the joint needs to do, how it will be loaded, and where it will sit.
Epoxy adhesives, for structural, load-bearing joints
Two-part epoxies are the go-to when a joint needs high mechanical strength, such as brackets, structural repairs, or metal components that will carry load or take an impact. They cure hard and resist creep under sustained stress far better than most other adhesive families. Many formulations also gap-fill well, which is useful when mating surfaces aren't perfectly flush, as is common in real-world fabrication and repair work.
GLUE GURU RAPID CURE Epoxy is a good general starting point for metal repair and fabrication work. It's an easy 1:1 mix that gels in 3 to 5 minutes, reaches handling strength in 10 to 20 minutes and is 100% waterproof, and it bonds metals as well as timber, fibreglass, ceramics and glass. For more demanding structural bonding, 3M Scotch-Weld DP420 is a toughened, high-performance two-part epoxy with high shear and peel strength, a 20-minute work life and temperature resistance of 120°C to 150°C. Epoxies also tend to offer good chemical and temperature resistance once cured, which makes them a reliable structural choice for engineering and metalworking applications.
The trade-off with epoxies is working time. Most need mixing in the correct ratio and have a set working window before they begin to cure, so they suit jobs where you can prepare the joint properly and work methodically rather than needing an instant fix.
Cyanoacrylates (super glue), for fast, small-area fixes
For small metal parts, quick tacking, or repairs where clamping isn't practical, a cyanoacrylate gives you a bond in seconds rather than hours. It's less suited to large surface areas, gap-filling, or joints under constant flex or vibration, since the cured film is quite rigid and brittle compared with epoxy or a hybrid polymer.
LOCTITE 401 Fast Cure Cyanoacrylate is a solid choice for small fittings and assembly work on metal, or for holding a component in position while a slower, stronger adhesive cures elsewhere on the same job. Where a small joint will take knocks, LOCTITE 435 is a clear, toughened grade. If you're bonding a metal part to polyethylene, polypropylene or another hard-to-bond plastic, LOCTITE 770 Primer prepares the plastic surface and also speeds up the cure, though it isn't recommended for joints that need high peel strength.
MS polymer / hybrid polymer adhesives, for flexible, weatherproof bonds
Where the joint needs to move slightly with thermal expansion, vibration, or ongoing outdoor exposure, an MS polymer adhesive is usually a better fit than a rigid epoxy. These stay flexible after curing, bond well to metal without always needing a primer, and hold up well to New Zealand's weather conditions, which makes them a common choice for construction, roofing flashings, cladding, and general fabrication work where a rigid bond would eventually crack under repeated movement.
QUILOSA MS35 is an MS polymer adhesive sealant for bonding and sealing dissimilar materials, including metal and aluminium, where movement and vibration are a factor. It adheres without primer to most materials, is neutral and non-corrosive to metals, has excellent UV resistance, and stays flexible from -40°C to +90°C. For jobs that need an immediate grab, QUILOSA FMS offers an instant-bond MS polymer formulation that's also low-VOC. Unlike many epoxies, MS polymers typically remain workable for longer, which is handy on larger installation jobs where you need time to align and adjust panels or flashings before the adhesive sets.
Contact and specialty adhesives, for laminating or bonding metal to other substrates
If you're bonding sheet metal to a backing material such as timber, laminate, or a composite panel, a contact adhesive designed for metal-to-substrate bonding often suits better than a pure metal-to-metal adhesive. Contact adhesives are applied to both surfaces, allowed to go tacky, then bonded under pressure, which gives an immediate grab that's useful for panel lamination work where clamping the whole assembly isn't practical.
CANTAC HIGH-TAC Aerosol Contact Adhesive and CANTAC ULTRA-TAC both suit sheet metal lamination work, and both come in canisters for larger panel jobs. For bonding rubber to metal, BOSTIK 2405 is a two-part, cold-curing adhesive that gives a tough, resilient bond to natural and synthetic rubbers, wood and metal.
Don't Skip Surface Preparation
More metal bonds fail from poor surface prep than from choosing the wrong adhesive in the first place. A handful of basics make a disproportionate difference to how long a joint lasts.
Clean thoroughly. Use an appropriate solvent cleaner such as GLUE GURU Acetone Solvent to strip oils, grease, and machining residue before applying any adhesive. Even a light fingerprint of oil can be enough to weaken a bond on metal.
Abrade smooth or oxidised surfaces. A light scuff with abrasive paper gives the adhesive something to key into and removes surface oxidation that would otherwise sit between the adhesive and the base metal.
Prime where recommended. A primer or activator is common with cyanoacrylates, and some epoxies and MS polymers also perform better on certain metals with a primer step. Skipping a specified primer is one of the most common reasons a "good" adhesive still underperforms on metal.
Let solvent cleaners flash off fully. Bonding over a surface that's still slightly wet with solvent can interfere with cure, particularly with moisture-cure chemistries like polyurethane and some MS polymers.
Consider the Environment the Joint Will Live In
New Zealand's climate is hard on outdoor bonds. UV exposure, coastal salt air, and the temperature swing between a hot summer day and a cold winter night all put ongoing stress on an adhesive joint over time. If the joint is outdoors, near the coast, or regularly exposed to moisture, prioritise adhesives specifically rated for UV and weather resistance rather than an indoor-only formulation.
This is especially relevant for marine fittings, external cladding, roofing flashings, signage, and anything bonded near the coastline, where salt-laden air accelerates corrosion at any point where moisture can get behind a bond line. A flexible, fully sealing adhesive like an MS polymer often outperforms a rigid epoxy in these conditions, because it moves with the joint instead of cracking and letting moisture in.
Getting the Application Right
Even the right adhesive underperforms with poor application technique. For structural or larger-area metal bonds, a proper cartridge or dispensing applicator gives a far more even bead and better control than squeezing straight from a tube. This is particularly important with two-part epoxies, where mix ratio and consistent, even application affect the final cured strength. The LOCTITE EPX Applicator Gun is built for two-part cartridges. For MS polymer cartridges, the SINTEX R26:1 MS Cartridge Gun gives consistent control on larger jobs, and the SINTEX R26:1S MS Sausage Gun does the same for 600ml sausages.
A few practical points worth keeping in mind on site:
Clamp or fixture where possible, even with fast-curing adhesives. Movement during the early cure stage is one of the most common causes of a weak or uneven bond.
Work within the adhesive's open time. Every chemistry has a window during which it bonds properly. Epoxies in particular will start to lose effectiveness once past their working time, even if they still look wet.
Mind the temperature. Cure speed and final strength for most adhesives are temperature-dependent, and a cold workshop or an outdoor job on a chilly morning can significantly extend cure times, especially for moisture-cure and two-part systems.
Don't rush load-bearing joints. A bond can feel solid to the touch well before it's reached full cured strength. For structural work, follow the manufacturer's full cure time before putting the joint under real load. DP420, for example, takes 3 days at 23°C to reach full cure.
A Quick Way to Decide
If you're still weighing it up, here's a simple way to narrow the choice down.
Need maximum strength for a structural or load-bearing joint? Epoxy adhesive, such as GLUE GURU RAPID CURE Epoxy or 3M DP420.
Need a fast fix on a small metal part? Cyanoacrylate, such as LOCTITE 401, or LOCTITE 435 where the joint takes knocks.
Need flexibility and weather resistance outdoors? MS polymer adhesive, such as QUILOSA MS35 or QUILOSA FMS.
Bonding metal to another material like timber or laminate? Contact adhesive, such as CANTAC HIGH-TAC, or BOSTIK 2405 for rubber to metal.
Joint involves dissimilar metals in a damp or outdoor location? A flexible, fully sealing adhesive to reduce galvanic corrosion risk.
Common Mistakes Worth Avoiding
A few recurring issues come up again and again with metal bonding, regardless of which adhesive is used.
Skipping degreasing because the metal "looks clean". Oils and light residue are often invisible until the bond fails.
Using an indoor-rated adhesive outdoors because it was already on hand, rather than checking the weather and UV rating.
Ignoring mix ratio on two-part epoxies, which directly affects both cure time and final strength.
Loading a joint too early, before the adhesive has reached its stated full cure strength.
Assuming all metal adhesives are interchangeable across aluminium, steel, and stainless steel. Alloy composition and surface finish change how well a given chemistry performs.
Final Thoughts
Choosing a metal bonding adhesive comes down to three core questions. What metals are involved, what load or movement does the joint need to handle, and what environment will it sit in? Get those three right, prepare the surface properly, and apply the adhesive within its recommended conditions, and the choice becomes far more straightforward than it first appears.
At Glue Guru, we stock adhesives across all of these categories, from structural epoxies and fast-curing cyanoacrylates to flexible MS polymer adhesives, and our team regularly helps engineering and metalworking trades match the right product to the job. If you're not sure which adhesive suits your specific metals, load requirements, or environment, get in touch with the team, and we'll help you find the right fit before you start.