Experts, how should we interpret the requirement in the standards that ‘coatings shall not be exposed to the air for long periods of time’? ?
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Big names, as the title suggests. In GB50726, what does clause 13.2.9, which states that \"coatings shall not be exposed to the air for long periods of time\", mean? Why can’t it be exposed to air? Thank you!
Dear experts, I’d like to ask for your advice! ! !
This refers to the primer coating; that is, once the primer has been sprayed and has dried into a film, the transition layer or topcoat should be applied as soon as possible, in order to prevent the primer from deteriorating or peeling due to prolonged exposure to air, and to avoid a decrease in the adhesion between the primer and the topcoat, which could ultimately affect the corrosion protection effect.
It’s probably a wording error in the standard formulation; coatings are meant for corrosion protection – so why not expose them to air?
Then why can’t the underlying layer be exposed for a long time? Is it because the components and principles of the underlying coating are different?
If the underlying coating has the same oxidation resistance, light resistance, resistance to rain wash, and other properties as the topcoat, then what is the need for a topcoat?
Okay, I’ve learned it*. It’s just different on the inside and outside!
That’s the requirement for zinc-rich primers, right? Generally, a topcoat is needed to provide shielding
It mainly depends on the components of the paint used; if it’s epoxy-based, it certainly cannot be exposed to air directly, while acrylic or polyurethane-based paints can be.
These are the specifications for epoxy zinc-rich and inorganic zinc-rich primers. Epoxy zinc-rich primers and inorganic zinc-rich primers are both primers; they have poor weather resistance and cannot be used as topcoats exposed to the outdoors for long periods of time. Apart from moisture-cured inorganic zinc-rich coatings, the curing agents for epoxy two-component coatings are mostly amines, which readily react with water in the air, resulting in white spots ； Zinc has a low potential, and prolonged exposure to air causes it to oxidize (forming white deposits), ultimately rendering some of the zinc powder ineffective and failing to achieve the desired anti-corrosion effect ； Inorganic zinc-rich coatings are porous after formation; these pores are not merely present on the surface’s surface layer – they may extend deeper. When exposed to air, capillary action can cause certain components that are not conducive to corrosion prevention to be drawn in, such as air with high chloride ion levels or moisture, especially in coastal areas. Therefore, it makes sense for the specifications to state that the surface should not be exposed to air; it is essential to apply intermediate and top coats to the dried zinc-rich primer surface as soon as possible, just as the first coat must be applied within 4 hours after sandblasting.