Grade stamp (timber)

A grade stamp is the inked or branded mark applied to each piece of structural timber by the manufacturer or grading mill. It is the visible evidence that the timber meets a stress grade, has been treated to the specified hazard class, and has been seasoned correctly. Without a legible grade stamp, a piece of timber cannot be relied on for AS 1684 span-table compliance, and the certifier can reject the framing at inspection.

What a typical stamp shows:

Stress grade: MGP10, MGP12, MGP15 for machine-graded pine; F5, F7, F8 for visually-graded pine and hardwood; F17, F22, F27 for high-strength hardwood and engineered timber.
Species or species group: P (pine), RP (Radiata Pine), HW (hardwood), Slash, Hoop, mixed-eucalypt species code.
Treatment hazard class: untreated (no mark), H1, H2, H2F, H3, H4, H5, H6.
Treatment chemical: ACQ, CCA, LOSP, Tanalith, Permapine, etc.
Seasoning: KD (kiln-dried), SD (seasoned, air-dried).
Mill or producer identifier: a code linking back to the mill of origin for traceability.

Some manufacturers add a date code, batch number, or moisture-content indicator. The exact stamp layout varies by mill; all stamps must carry the structural information either as text or as an interpretable code.

Why the stamp matters at framing inspection. The certifier looks for at least one legible stamp on every load-bearing member. For multi-piece members (built-up beams, top plates run from multiple lengths), each piece must show a stamp. Common defects:

Stamp on the bad face, fixed inwards or covered by another member, so the stamp is not visible.
Stamp worn off by long site storage in weather (UV-degraded ink, wet weathering).
Stamp on the off-cut end, with the visible end un-stamped.
Wrong grade: an MGP10 piece used where MGP12 was specified, with the stamp showing the actual grade.

Treated timber stamps are typically a different colour (often green-ink) for visibility and may include the hazard class as a separate stamp. Treatment to the wrong hazard class is a structural and durability defect (e.g. H2 in a deck application that needs H3).

For builders.

Reject unstamped or illegible-stamped timber at delivery. Once it’s in the frame the cost of removal is significantly higher than the cost of an alternative load.
Set the stamps facing out during framing so the inspector can read them without dismantling.
Keep delivery dockets. Where the stamp is unclear, the docket and mill’s certificate of grading is the back-up evidence.

Also known as: timber stamp, grade brand, stress stamp.

Category: Materials / timber / grading.

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