Architectural Flashing Supply
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Hems, returns, locks and seams · Lesson 4 of 4

Hems, returns, locks and seams: defects, verification and case study

What to check on every hem and seam, the defects that recur and their causes, and a copper seam case worked from finding to decision.

You will be able to: Inspect hems and seams against the order and the sources, diagnose the common defects, and document the evidence and the fix for review.

8 min · 10 slides · 6 questions

All lessons in this module
Slide 1 of 10

Check every hem

Before a hemmed piece is packed:

  • Material and thickness as ordered
  • Return length as ordered, never under 0.375 in
  • Hem type and gap as ordered
  • Hem on the ordered face, painted face where it should be
  • No cracking in the coating on painted folds
Eight checks on hems and seamsEight numbered tiles for inspecting hemmed pieces and seams before they are packed or accepted.12345678Material andthicknessReturn length0.375 in minHem typeand gapHem face andpainted sideNo coatingcracks on foldsLock fullyengagedSeam uniformalong its lengthFinish clean,no roller marks

Eight numbered tiles: material and thickness, return length, hem type and gap, hem face and paint, coating on folds, lock engagement, seam uniformity, and a clean finish.

1
Material and thickness as ordered (the order; AFS material register)
2
Return as ordered, at least 0.375 in (AFS limits)
3
Hem type and gap as ordered (FlashDraft)
4
Hem face and painted side as ordered (FlashDraft, the order)
5
No cracking in the coating on folds (coil maker's bend rating)
6
Lock fully engaged to the detail's fold depth (CDA copper flat lock: 3/4 in)
7
Seam uniform along its length (MCA)
8
Finish free of roller and debris marks (MCA)
Each check names its source in the legend: the order, AFS limits and FlashDraft, the coil maker, the CDA (copper) and MCA (roof seaming).

Glossary

Lock engagement
How far the folds of a lock overlap one another, checked against the fold depth in the detail.
Uniform appearance
MCA's first visual check of a finished seam along its length.
Coating crack
A split in the paint on the outside of a fold bent tighter than the coating allows.