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Metals, alloys and protective coatings · Lesson 4 of 4

Metals, alloys and protective coatings: defects, verification and case study

A seven-tile inspection guide that pairs each symptom with its likely cause, an illustrative coastal case worked through to its requests for information, and the job packet that records it.

You will be able to: Diagnose the common coating and corrosion defects from what you see, name the usual cause and correction, and document evidence and open questions in a job packet.

8 min · 11 slides · 6 questions

All lessons in this module
Slide 1 of 11

Seven things to look for

Each tile in the drawing pairs a symptom you can see with its usual cause. For every one:

Record a photo, the location, the material and finish from the order, what the part touches and what drains onto it.

Seven things to look for on coated and bare metalSeven rows pairing a symptom with its usual cause and what to record: white deposit on bundles, corrosion along pencil layout lines, streaks below copper or a drain, corrosion at treated wood, a corroded small fastener, chalky paint, and film left on or the wrong color.Seven things to look forSymptom, usual cause, what to record1White or gray bulky deposit onbundled partsCause: Wet storage stainRecord: Photo, were bundles wet, lightor heavy2Corrosion along pencil layout linesCause: Graphite pencil marksRecord: Photo, how lines were marked3Streaks or corrosion below copper ora drainCause: Copper runoff or condensateRecord: Where the water comes from4Corrosion where metal meets treatedwoodCause: No barrier at treated lumberRecord: Treatment type, barrier used5Corroded small fastener in a largesheetCause: Area ratio or wrong fastenerRecord: Fastener metal, sheet metal,sizes6Chalky or faded paintCause: Finish wear; check its data sheetRecord: Finish, chart, color name,exposure7Film left on, or color not asorderedCause: Film not removed, chart not namedRecord: Order line with chart andprinted nameAlways add: a photo, the location, and thematerial and finish from the order.

Seven numbered rows pairing a symptom with its usual cause and what to record: white deposit on bundles, corrosion along pencil layout lines, streaks below copper or a drain, corrosion at treated wood, a corroded small fastener, chalky paint, and film left on or the wrong color.

1
White or gray bulky deposit on bundled parts
2
Corrosion along pencil layout lines
3
Streaks or corrosion below copper or a drain
4
Corrosion where metal meets treated wood
5
Corroded small fastener in a large sheet
6
Chalky or faded paint
7
Film left on, or color not as ordered
An inspection guide built from the AGA, MCA and coating-maker sources in this module. Record a photo, the location, and the material and finish from the order.

Sources

Videos for this lesson

What this video shows: A steel maker explains what the white powdery coating called white rust is, how it occurs and how to prevent it. Checked against the video's description.

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

What this video shows: A panel-industry discussion of what chalking and fading are and what causes them. Checked against the video's description only.

Video: How Does Metal Roof Paint Wear Out? Chalking And Fading by The Metal Roofing Channel, on YouTube. Chosen from the video's published description.

Glossary

Wet storage stain
A bulky white or gray deposit on new galvanized parts that were stored damp with poor ventilation; a light stain may not shorten the product's life.
Chalking
The powdery breakdown of a paint film as it weathers; the AAMA tiers measure chalk resistance along with color retention.
Job packet
The set of records kept with an order: spec line, material, finish chart and color, contacts, screening results, storage notes and requests for information.