Coating Application Techniques Flashcards

Before coating application, the steel surface temperature must be at least how far above the dew point, per common industry practice?

Answer: 5°F (3°C)

Industry practice and most specifications require the surface to be at least 5°F (3°C) above the dew point to avoid condensation.

An inorganic zinc-rich primer is applied too thick. Which defect is most likely?

Answer: Mud cracking

Inorganic zinc silicates are prone to mud cracking when applied above the maximum recommended DFT.

Why must zinc-rich primers be agitated continuously during application?

Answer: To keep heavy zinc dust in suspension so that the zinc loading stays uniform

Zinc dust is dense and settles quickly, so continuous agitation keeps the zinc content in the applied film consistent.

A freshly applied amine-cured epoxy shows a greasy, waxy surface film after curing in cool, humid conditions. What is this defect, and what is the typical remedy before recoating?

Answer: Amine blush; wash with clean water and detergent, then rinse

Amine blush is a water-soluble carbamate that must be removed by washing before recoating to avoid intercoat adhesion failure.

What is a key reason for applying a coat after the minimum recoat time but before the maximum recoat window ends?

Answer: To ensure good intercoat adhesion without having to abrade the surface

Recoating inside the window allows chemical or mechanical bonding between coats, while going past it often requires abrading or a tie coat.

Which application practice best reduces dry spray on a hot, windy day?

Answer: Holding the gun at the correct distance and using a slower-evaporating thinner within the manufacturer's limits

Dry spray happens when droplets lose solvent before they reach the surface, so a closer, correct distance and a slower thinner help.

Why is rolling usually avoided for the first coat of a zinc-rich primer over a blasted surface?

Answer: Rolling may not wet the anchor profile fully and gives uneven zinc distribution

Spray drives the primer into the surface profile and gives even zinc loading, which rolling does not reliably achieve.