Quick answer: The performance of a zinc-rich coating is controlled more by surface preparation and application quality than by marketing claims. The steel must be free from oil, salts, rust, mill scale, dust and moisture; environmental conditions must prevent condensation; the material must be fully mixed; and the specified dry film thickness must be measured after curing.

This guide is the execution and quality-control pillar for Marjan Polymer Industries. It is not a substitute for the manufacturer TDS or a contractual coating specification.

Use it to build a documented process from pre-inspection through final DFT and defect repair.

Pre-Job Review

Confirm the substrate, existing coating, exposure environment, repair boundaries, required standard, product, batch, target DFT, application method and acceptance criteria before work begins.

Identify inaccessible surfaces, sharp edges, welds, bolts, pits and complex geometry. These areas often receive less film than large flat surfaces and may require stripe coating.

Contamination Assessment

Oil and grease prevent adhesion. Soluble salts attract moisture and can cause blistering or underfilm corrosion. Dust interferes with bonding and can create a weak layer. Moisture or condensation can trap water beneath the coating.

Use an approved degreasing procedure, clean water for salt removal where required, and suitable inspection methods. Do not rely on visual appearance alone when the service is severe.

Mechanical Preparation

Abrasive blasting is preferred where a high-performance, long-term system requires a defined cleanliness and profile. Power-tool cleaning may be suitable for local repair or specified galvanized surfaces.

The selected preparation grade must be written into the job specification. The final surface should be compared with the relevant standard and checked across edges, welds and recesses.

Environmental Conditions

Record ambient temperature, surface temperature, relative humidity and dew point. The substrate must remain free from condensation during preparation and application.

Manufacturer limits are mandatory, but the project may require a larger dew-point margin. Stop work during rain, mist, dust events or conditions that contaminate the prepared surface.

Mixing and Material Control

Verify product identity, batch, shelf condition and container integrity. Zinc-rich materials settle heavily and require power mixing until compact sediment is fully reincorporated.

Record thinner type and addition. Excessive or unapproved thinner changes deposited solids, sag resistance, drying and final DFT.

Application Control

Use a written sequence for stripe coating, first coat, recoat interval and second coat. Monitor wet film where appropriate and use test areas to establish the relationship between application technique and cured DFT.

Maintain agitation during spray application. Control gun distance, angle, overlap and speed. Avoid dry spray, pinholes, runs and shadowing behind stiffeners or bolts.

Dry Film Thickness

Measure DFT only with a suitable calibrated instrument and according to the agreed inspection plan. A single reading is not representative of a large structure.

Record individual readings, spot averages, locations and acceptance limits. Investigate both low and excessive thickness because under-build reduces protection while excessive zinc-rich film may crack or mud-crack.

Defect Repair

Mark missed areas, thin film, contamination, loss of adhesion, cracking, runs and mechanical damage. Define the boundary, prepare the defect and surrounding sound coating, then reapply the specified material.

Do not simply paint over a defect without removing the cause. Retest DFT and appearance after repair.

Inspection Record

• Project and component identification.
• Product, batch and expiry.
• Preparation method and standard.
• Environmental readings and time.
• Mixing and thinner record.
• Application method and coat times.
• DFT readings and gauge calibration.
• Defects, repairs and final acceptance.

Frequent Failure Causes

Common failures include coating over salt-contaminated steel, insufficient blast cleaning, incomplete mixing, zinc settlement, applying too thinly on edges, condensation, premature recoating, incompatible topcoat and unmeasured DFT.

A disciplined inspection record is more valuable than adding extra marketing language to the product page.

Frequently Asked Questions

Is visible clean steel enough?

Not always. Soluble salts, oil and fine dust may remain even when the surface looks clean.

Why is zinc-rich paint difficult to spray uniformly?

Dense pigment settles and complex geometry creates shadowing. Agitation, equipment selection and technique are critical.

Can DFT be estimated from the amount of paint used?

Consumption is useful for planning, but acceptance should be based on calibrated DFT measurements.

What should be inspected first?

Surface condition and environmental controls. A perfect topcoat cannot correct a contaminated substrate.

Should edges receive extra attention?

Yes. Edges and welds often receive lower film build and may require stripe coating.

Technical References

1. ROVAL Technical Data Downloads
2. ASTM A780/A780M-20
3. American Galvanizers Association – Zinc-rich paint

Technical notice: This guide does not replace the current manufacturer TDS, SDS, contractual coating specification or site-specific engineering assessment. Confirm the latest documentation before use.