Plastic-to-metal is two different surfaces pretending to be one joint. Metal wants an adhesive that wets oxides and fills gaps. Plastic wants an adhesive that can stand peel and thermal expansion. The glue that wins on steel can be useless on polypropylene.
Numbers below are the typical ratings in our adhesive–material matrix (modeled bond class and psi), not a certified lab report for your exact batch. Use them to eliminate the wrong chemistry before you spend money.
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What the matrix says (plastic vs metal)
| Adhesive type | Steel | Aluminum | ABS | PVC | PP | HDPE |
|---|---|---|---|---|---|---|
| Two-part epoxy | Good (3000 psi) | Excellent (6000) | Good (5000) | Fair (600) | Fair (1000) | Fair (400) |
| Cyanoacrylate | Good (700) | Excellent (7000) | Good (7000) | Good (1500) | Fair (500) | Good (750) |
| Plastic-repair epoxy | Poor (150) | Fair (1500) | Good (5000) | Good (700) | Poor (730) | Fair (400) |
| Metal epoxy | Good (750) | Excellent (4500) | Fair (3000) | Fair (3000) | Poor (370) | Fair (250) |
| Structural acrylic | Poor (200) | Fair (1000) | Poor (300) | Poor (300) | Poor (150) | Fair (400) |
| PVA wood glue | Poor | Poor | Poor | None | None | Poor |
Read the table as a filter. PVA is out. Generic metal-filled epoxy is built for steel, not for a flexible bumper. Two-part epoxy is the default for a load-bearing ABS or nylon bracket on aluminum. Cyanoacrylate is the default for a small, close-fitting, indoor part.
Identify the plastic before you open a tube
The recycling mark is not decorative:
- ABS, PVC, PC, nylon, PETG: epoxy or CA can work after sanding.
- PP (5), PE/HDPE (2/4): low surface energy. Plan on primer, flame treatment, or a mechanical joint. Expect peel failures if you skip that.
- PTFE: almost nothing sticks. Redesign the joint.
If you cannot identify it, work through the material quiz rather than guessing “plastic.”
Best default: two-part epoxy
A filled a two-part epoxy wets both metal oxide and a sanded polymer, fills a gap, and does not rely on a hairline fit. Clamp or tape until the working time ends. For a steel bracket, J-B Weld is the metal-oriented cousin — strong on aluminum in our matrix, only fair on PP, which matches how people actually break bumper tabs.
Surface prep is the whole job: solvent degrease the metal (IPA, not oily brake cleaner residue), sand both sides, degrease again, mix equal parts until uniform, apply to both faces, clamp.
Best for small parts: gel cyanoacrylate
Loctite Super Glue Gel Control earns its keep on a tight joint: a screw boss, a magnet in a housing, a broken ABS tab with no gap. The matrix’s high numbers on ABS assume that fit. A gap thicker than a business card is an epoxy job. CA is brittle in peel — a car interior tab that gets yanked is the wrong use.
Thermal expansion and why a “strong” joint still peels
Aluminum expands more than steel; both expand more than most filled epoxies; unfilled CA barely moves at all. A long, thin bond line on a sun-loaded part sees peel at the ends even if the coupon psi looked excellent. Keep overlaps short and wide, or switch to a slightly flexible two-part (a methyl-methacrylate / structural acrylic) when the assembly will cycle hot-cold. Our acrylic row is only fair on aluminum — that is a reminder to buy a structural MMA, not a craft acrylic glue.
Nylon is worse: it absorbs water and grows. A dry-fitted nylon clip glued to steel in a heated apartment can split the glue in the first humid week. Mechanical backup (a screw, a heat-set insert) is not a cop-out; it is how those parts were designed.
Metal-to-metal is a different article
If both sides are metal, skip plastic-repair epoxies and read best glue for metal to metal. If the “plastic” is vinyl upholstery on a metal frame, you want a flexible contact adhesive, not epoxy: leatherette and vinyl.
FAQ
Strongest glue for plastic to metal?
Two-part epoxy for most rigid plastics. CA for tiny close fits. PP and PE need primer or a different joining method.
Will super glue work?
On small, well-fitted ABS or PVC parts, yes. It peels under vibration and heat, and it is only fair on polypropylene in our matrix.
Do I sand the metal?
Yes. Degrease and scuff. Smooth oily aluminum is why strong glues fail.
Polyethylene to steel?
Not with ordinary epoxy or CA if you need a structural bond. Primer, flame treat, or fasten mechanically.