Why some coatings need it
In some two-component epoxies, the base and the curing agent are not fully compatible at the moment of mixing. A short standing period lets the first reactions start, improves compatibility between the components and stabilizes the mixture. Products formulated with certain amine or polyamide curing agents are the usual examples. Many modern formulations have no induction time at all, which is why the data sheet is the only reliable reference.
What happens if it is skipped
When the mixture is applied too early, the film may show:
- amine blush, a greasy or waxy surface layer that interferes with the next coat;
- slower or incomplete cure, with lower hardness or chemical resistance;
- surface defects such as cratering or poor flow;
- weak intercoat adhesion if the next coat goes on over a contaminated surface.
Induction time, pot life and recoat window
| Term | Clock starts | Purpose |
|---|---|---|
| Induction time | At mixing | Minimum wait before application |
| Pot life | At mixing | Maximum time the mix remains usable |
| Recoat window | At application of the coat | Minimum and maximum time before the next coat |
The induction period is taken out of the pot life, not added to it. At high temperatures the reaction runs faster and induction usually becomes shorter, while the pot life also shrinks. At low temperatures the induction period is often longer, and some data sheets give separate values by temperature range.
Field practice
- Mix the full kit as instructed, then let it stand covered for the stated period.
- Keep the material within the temperature range on the data sheet before and during the wait.
- Stir again briefly before application if the manufacturer calls for it.
- Record mixing and start times when the quality plan requires traceability.
- Check the substrate against the dew point during the wait, since conditions can change.
Products with no induction time can be applied as soon as they are mixed, as their data sheet states.
Application practice for shop and field work is covered by SSPC-PA 1, which refers to the manufacturer's instructions for these timing limits. Our protective coatings service follows the data sheet timings on every mix.