How to Store Galvanized Structures and What White Rust Is

What white rust is

White rust is a white or light grey layer of zinc oxides and hydroxides on a galvanized surface. What corrodes here is the zinc of the coating, not the steel beneath it. The deposit is loose, and on new shiny zinc it is visible at once.

It has nothing to do with the galvanizing process itself: it appears after the bath and depends on storage conditions. So it is within your power to avoid it, even when the coating was applied to every requirement.

Among other coating defects, white rust is covered in the reference Hot-dip Galvanizing Defects. Here we deal with one thing only: how to keep the deposit off in the yard, and what to do once it has formed.

Why galvanized steel turns white

White rust grows from water. A damp stack, condensation inside packaging, rain that got between the parts: each keeps a film of water on the zinc, and it has nowhere to dry. Acid vapours and salts in the water speed things up.

It is worst when parts sit tight against each other or are wrapped in film: water creeps into the gaps and air does not follow. On an open surface swept by wind the water dries fast, so there is less deposit.

Fresh zinc is the most vulnerable. The protective zinc carbonate layer has not formed on it yet, and it is on newly galvanized parts that this kind of attack is most often seen.

White rust and red rust: how to tell them apart

The colour of the deposit hints at what is corroding. White is zinc, and the steel under it is still covered. Red-brown needs a closer look, because the causes differ.

When the alloy layer corrodes, iron hydroxide comes out through the pores and gives the brown colour. The steel remains protected by the iron-zinc alloy.

How to store and stack galvanized parts

There is one rule: water must not stand on zinc. Everything else follows from it.

• choose a dry, ventilated place with no condensation;
• put spacers between the parts so air moves freely;
• build the stack at a slope so water runs off instead of pooling in pockets;
• lift the parts off the ground so moisture does not collect underneath;
• keep salt, de-icing agents and aggressive fumes away from the yard.

Parts that will sit in storage for a long time need this most. If you know that in advance, tell the plant before galvanizing: it is easier to agree on storage beforehand than to fight the consequences.

A light oil film is sometimes applied, but it does not give complete protection. It is no substitute for a dry store.

What to do if the deposit has appeared

First remove the cause, which is water: take the stack apart, lay the parts out with gaps and spacers, and let them dry. Leaving them in the same conditions makes no sense.

Then assess how serious the deposit is and check the coating thickness. Wet storage stain alone is not grounds for rejection if the thickness is not below the minimum under DSTU EN ISO 1461:2024. So the measurement decides, not the colour.

A loose deposit is taken off with a soft brush, not a steel one. Chips and scratches, if there are any, are closed with zinc-rich paint or by spraying.

If the structure will be painted after galvanizing, the deposit is removed from the surface completely: on older zinc, dirt, grease and white rust are cleaned off, and then it is prepared for paint. The sequence for a duplex system is on the powder coating page.

What not to do

• wrap fresh galvanized parts in shrink film: it traps water;
• pile parts in a tight stack with no spacers;
• put galvanized structures right against wet lime or cement without protection;
• keep them next to uncoated steel where rain or wind can carry rust onto the zinc;
• assume that oiling replaces a dry store.

How to design a structure for galvanizing and what to agree with the plant before dipping is in Designing Structures for Hot-dip Galvanizing.

Galvanizing at POLYGONAL and cost estimate

The POLYGONAL company carries out hot-dip galvanizing of steel structures in its own bath measuring 13,000 × 1,600 × 3,200 mm, mass of a part up to 7 t, with no minimum order. We accept parts for galvanizing from customers across Ukraine; delivery is charged separately.

The hot-dip galvanizing calculator gives a rough price from weight and dimensions. How long the coating lasts in different environments is explained in Hot-dip Galvanizing Service Life. If galvanizing is part of a larger order, see steel fabrication and hot-dip galvanizing.