"Is the glue flame-retardant?" is usually the wrong first question — and buyers who ask it are often sent the wrong product. What a fire authority, a shipyard or a door certifier actually checks is how the bonded assembly behaves in fire, and which test standard the evidence comes from. This article explains the fire-performance evidence behind our own PU adhesives — what was tested, to which standard, and which grade fits which job — so you can match it against your specification instead of a marketing word.
Three Different "Fire" Claims, Three Different Tests
- Reaction to fire of the material (GB 8624). China's classification standard for building materials — the one door plants and panel makers are usually asked for. Alongside the burning behaviour class, assemblies are assessed for smoke toxicity, reported as a ZA rating.
- Surface flame spread (IMO Res. A.653(16)). The marine test: how flame propagates across a surface. Required evidence for materials going onto ships and offshore structures.
- Bond strength retention. No burn test replaces it: a fire door only works if the skin stays on the core. Strength values to GB 6329 are part of the same evidence pack.
A supplier should be able to tell you which of these their product has actually been through. Here is ours.
The 1K Grade: MPU-20
MPU-20 is a single-component, solvent-free moisture-curing PU developed for fireproof door assembly — bonding steel, wood and mineral faces to perlite, rock-wool, magnesium and calcium-silicate cores. It is tested under GB 8624 with a ZA1 smoke-toxicity rating, and is formulated without formaldehyde or toluene.
| Property | Value |
|---|---|
| Type | 1K solvent-free moisture-cure PU |
| Viscosity | 5–20 Pa·s |
| Non-volatile matter | ≥94% |
| Coating weight | 180–200 g/m² |
| Open time / cure | >45 min / 4–5 h |
| Bond strength | ≥15 MPa metal-to-metal (GB 6329); substrate failure on fireproof and insulation boards |
In practice this is the grade we quote when a fabricator asks for "one-component, not flammable, for panels": it is solvent-free (nothing volatile to flash off), cures with ambient moisture, and its fire evidence comes from the door industry it was built for. It is also our standard grade for paper honeycomb panel bonding, where the same non-combustibility questions come up.
The 2K Grade for Marine Work: PU-50
Where the specification is marine — engine-room insulation, ship interior panels, liquefied-gas tanker tank insulation — the evidence needed is different, and so is the grade. PU-50 is a two-component solvent-free PU whose low flame spread is tested to IMO Res. A.653(16). Two figures worth noting from its TDS:
- Tensile strength metal-to-metal ≥10 MPa at 23°C, and metal-to-polystyrene joints fail in the polystyrene, not the glue line;
- Tested tensile strength of ≥12 MPa at −137°C — cryogenic service on gas-carrier insulation, which is about as hard a cold-performance requirement as adhesives face.
Pot life is under 60 minutes at room temperature at a coating weight of about 180 g/m².
How to Ask a Supplier (Including Us)
- Name the standard your certifier will ask for — GB 8624 class for building assemblies, IMO A.653 for marine surfaces. "Flame-retardant" without a standard is not evidence.
- Ask for the smoke rating, not just the burn class. Smoke toxicity (ZA rating) is assessed separately and matters for occupied buildings.
- Ask how strength was measured. GB 6329 metal-to-metal values and substrate-failure results on your actual face/core pair are what your door or panel test will stand on.
- Test your own build-up. Certificates travel with the assembly, not the drum: we supply TDS, samples and the fire-test documentation for your own qualification run.
FAQ
Does a flame-retardant adhesive make the panel fireproof?
No. Fire classification belongs to the assembly. The adhesive's job is to contribute no readily-ignitable mass (solvent-free helps), keep smoke toxicity low, and hold the skins on — the panel's rating comes from the whole build-up under test.
Is a 1K or 2K grade better for fire-rated work?
Neither is "better" — they carry different evidence. MPU-20 (1K) carries GB 8624 / ZA1 door-industry evidence; PU-50 (2K) carries IMO A.653 marine evidence with cryogenic strength data. Start from the standard your certifier names.
Can MPU-20 bond aluminium honeycomb?
For aluminium honeycomb we normally quote a dedicated 2K grade — see the aluminium honeycomb adhesive page. MPU-20 is the paper-honeycomb and fire-door grade.
What documentation do you provide?
TDS, MSDS, fire-test documentation and free samples ahead of any bulk order.
Full assembly details are on the fire-door adhesive application page; for marine and cryogenic jobs, contact us with the specification and we will confirm the grade in writing.