How to Apply Fireproof Paint over Anti-Corrosion Primer (Compatibility Guide)

3) Primer selection rules (what engineers should specify)

Your goal is to specify a primer that is:

• Anti-corrosive enough for the service environment.

• Compatible with the intumescent product (approved system).

• Applied at an acceptable DFT and within defined recoat intervals.​

Common primer families used under intumescent (general industry practice)

Many intumescent systems allow epoxy or alkyd primers, but some systems caution against certain zinc-rich primers or primer types unless explicitly approved. Always verify approvals and compatibility lists from the intumescent system supplier.​

Primer DFT matters

Industry guidance notes that primers are often approved up to a maximum DFT, because excessive primer thickness can increase the risk of adhesion loss under fire exposure. This is why primers are tested and specified within limits as part of the full system approval.

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7) Common compatibility failures (and how to avoid them)

Problem 1: Intumescent delaminates from primer

Common drivers:

• Primer not approved/compatible.

• Primer DFT too high.

• Primer contaminated or over-aged before recoating.​

Preventive actions:

• Use an approved primer list for the chosen intumescent system.

• Control primer DFT and recoat window.

• Sweep blast/clean aged primer before applying intumescent.​

Problem 2: Cracking, mud-cracking, or sagging

Common drivers:

• Over-thickness in a single coat.

• Poor curing conditions.

Preventive actions:

• Apply in multiple passes to reach target DFT.

• Follow temperature/humidity limits from the product data.​

Problem 3: Exterior intumescent degrades early

Common drivers:

• Missing or incompatible topcoat.

• Inadequate sealing thickness.

Preventive actions:

• Specify a compatible sealer/topcoat for humid/outdoor exposure.