How long should epoxy primer typically cure before sanding or topcoat?

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Epoxy primer needs to reach a stage where the solvents have flashed and the film is ready for sanding or receiving the next coat. Because each product formulation, plus temperature, humidity, and film thickness, can change how long that takes, the correct cure/sand time is whatever the product label specifies. In many automotive primers at typical room temperature, that window is about 30–60 minutes, but some products may require longer. Following the label ensures the primer is sufficiently dry to sand or topcoat without smearing or trapping solvents, and it provides the right surface texture for proper adhesion. If you wait too long beyond the specified window, adhesion and intercoat bonding can suffer; if you go too soon, you risk damage by sanding through or smearing uncured material.