Architectural Flashing Supply
Start a Quote
Handling, storage and introductory quality control · Lesson 2 of 4

Handling, storage and introductory quality control: materials, standards and design constraints

How water with no air stains zinc, painted steel and aluminum, why cold metal sweats, the time limits publishers give, and which rules and whose advice apply.

You will be able to: Name what zinc-coated, painted and aluminum sheet each fear in storage, explain condensation and dew point, recognize the time limits publishers give, and say whose rule applies in the shop, on a jobsite and from a supplier.

14 min · 12 slides · 12 questions

All lessons in this module
Slide 1 of 12

Water with no air: zinc

GalvInfo says storage stain on galvanized sheet is a corrosion product, typically white, that forms when sheets in close contact get wet without free air circulation.

The American Galvanizers Association calls wet storage stain a bulky white or gray deposit caused by accelerated corrosion of the zinc coating.

GalvInfo adds that if galvanized steel is kept dry, white rust will never be an issue.

How water gets trapped between sheets, and how spacers let air inTwo end views. Left: six red sheets lying in contact, blue arrows for rain or condensation entering, steel blue beads (label B) of water trapped between the sheets with no air path, so the water stays. Right: three red bundles separated by spacer strips, with teal arrows showing air moving through each gap and carrying moisture away.Tight stackSpaced stackABwater staysno air to dry itair carriesmoisture offCDSchematic, not to scale

Two end views. Left: six red sheets lying in contact, rain or condensation arrows entering, steel blue beads of water trapped between the sheets with no air path, so the water stays. Right: three red bundles separated by spacer strips, with teal arrows showing air moving through each gap and carrying moisture away.

A
Sheets lying in close contact
B
Water trapped between the sheets (steel blue beads). Blue arrows are rain, snow or condensation reaching the stack; the red arrow with an X means no air can move
C
Spacer strips that hold bundles apart
D
Air moving through the gap and carrying moisture away (the green check marks the open air path)
The mechanism GalvInfo, AGA and the Aluminum Association describe: moisture between close surfaces with no air makes stain; air movement dries it. Schematic, not to scale.

Sources

Videos for this lesson

What this video shows: A steel maker explains what white rust is, how it occurs and how to prevent it. The slides give the sourced facts.

Video: What is white rust? by SSAB, on YouTube. Chosen from the video's published description.

Glossary

Wet storage stain
A white, gray or black corrosion deposit on zinc-coated steel that forms when closely packed surfaces get wet and stay wet without air movement. Often called white rust.
Water stain
The stain that forms on aluminum when water is trapped between wraps, sheets or other mating surfaces with no air flow to remove it.
Condensation
Water that comes out of the air onto a surface colder than the air's dew point.
Dew point
The temperature at which water vapor in the air begins to condense. It rises with air temperature and humidity.
FIFO
First in, first out: use the oldest stock first, so no material sits in storage longer than it has to.
Strippable film
A temporary protective plastic film on a finished face that is removed by a deadline set by the maker.