A protective coating fails at the steel underneath it, not in the tin.

A specification should name a standard for every stage of the work: the cleanliness grade, the profile range, the number of coats, the nominal and minimum dry film thickness, and the points at which the job stops for inspection. A specification that names only the product leaves every later argument unresolved, because there is nothing to measure the work against.

Hold points matter more than the final inspection. Once the top coat is on, nothing underneath it can be verified without destroying the film. Agree in advance which stages stop for inspection, who signs them off, and what happens when a stage fails. This is the single cheapest thing a client can insist on, and the one most often left out.

Conditions at the moment of application govern whether work can proceed at all. Relative humidity, dew point and steel temperature are recorded at each coat for a reason: those records are what settle a warranty claim two years later, when the coating has blistered and nobody can remember what the weather was doing.