Fireproofing over primed or painted steel: confirm the approved substrate route
Grey-primed steel arrives at a food-processing plant shortly before the spray crew mobilizes. The delivery paperwork does not identify the primer, and it differs from the approved information. The foreman proposes a small trial patch so the programme will not slip.
Do not decide to spray from the primer's colour or a trial patch alone. Identify the coating and compare it with the actual fireproofing design and manufacturer's requirements, then obtain the project's documented substrate decision. A test or bonding agent may form part of an accepted route, but does not automatically authorize an incompatible or unlisted construction.
Resolve the coating before application
- Identify what is on the steel. Request the fabricator's coating record, product identification, affected member list and any later touch-up information. Compare those records with the approved submittal. Mark unknown or inconsistent members on a location plan so a decision for one coating is not casually extended to every delivery.
- Open the relevant compatibility guidance. Check the complete design information and the fireproofing manufacturer's published substrate instructions. Certification guidance requires preparation and coating compatibility appropriate to the certified construction. Record the actual reference and uncertainty instead of writing 'all grey primer accepted' on the inspection sheet.
- Ask for the permitted technical route. Send the coating identity, member locations and proposed fireproofing arrangement to the manufacturer and responsible consultant through the project process. Ask whether further evidence, preparation or a different arrangement is required. Do not nominate a convenient bonding product as the answer before that review.
- Agree any test plan before testing. If the accepted route calls for testing, confirm the agency, method, representative locations, timing and criteria from the actual requirements. Record what the test can establish and which decisions remain outstanding. A visually sound sample or isolated bond result cannot establish all the fire-resistance design conditions.
- Separate preparation from acceptance. Have the responsible trade complete the directed surface work and document the affected locations. The opened Canadian product instructions provide an example of checking steel cleanliness and asking the architect about primed steel's tested arrangement. Their product-specific procedure is not a rule for every material.
- Release only the resolved scope. Obtain the required written decision and keep its conditions with the work pack. Tell the applicator which member types and coatings it covers. Leave unresolved members out of that release and record any coating change during later deliveries as a new question.
Common mistakes
- Using primer colour as product identification.
- Calling a bonding agent an approval without the governing decision.
- Extending a test result to different coatings or member conditions.
Checklist
Keep a substrate decision record
- Coating identity and affected members.
- Compatibility references and open questions.
- Directed preparation or test arrangement.
- Evidence with its location and limits.
- Written release conditions and later changes.
Check your understanding
The trial patch remains attached. Does that let the crew spray every primed beam?
Show the answer
Confirm the applicable design and recorded substrate decision first. The patch does not identify every coating, represent every member condition or prove the complete system's fire-resistance suitability.
