Moisture content (MC)
Moisture content is the weight of water in timber as a percentage of oven-dry weight. AS 1080.1 test method. EMC, KD seasoning, and on-site MC checks for builders.
Ask Chalkline about this →Moisture content (MC) is the weight of water held in a piece of timber expressed as a percentage of the timber’s oven-dry weight. The standard test method is AS/NZS 1080.1, which measures MC by oven-drying a sample piece, weighing before and after, and computing the loss as a percentage. On a build site, builders use a portable moisture meter (pin-contact or pinless capacitance) to get an approximate reading without destroying the piece.
Why MC matters:
- Timber shrinks as it dries below ~25% MC and swells as it rewets. The shrinkage between delivery and equilibrium with the building’s interior is what causes frame distortion, screw pops, joint cracking, and finished-trim gaps.
- AS 1684 publishes separate span tables for seasoned (MC ≤15%) and unseasoned (typically 25%+) timber because the strength values differ.
- Adhesive bonds (glue, joint compound) fail or weaken on timber above ~18% MC.
- Paint and stain films crack or blister on substrates above ~18% MC at application.
The three reference MC values:
| Term | Typical value | Meaning |
|---|---|---|
| Green | 25% to >50% | Just-sawn, unseasoned timber. |
| Seasoned / KD | ≤15% | Kiln- or air-dried below the seasoned threshold; standard for residential pine framing. |
| Equilibrium MC (EMC) | 8% to 15% | The MC the timber settles to once it reaches equilibrium with the surrounding air’s relative humidity and temperature. Varies by location: Sydney coastal interior ≈ 11-13%, Darwin wet season ≈ 16-18%, Alice Springs dry interior ≈ 8-10%. |
A seasoned-pine frame installed at 12% MC in Sydney and dried to its EMC of 11% will shrink negligibly. The same frame in Cairns will rewet to ~16% EMC and swell.
On-site MC checks. Builders should spot-check moisture content with a meter at three points:
- At delivery: confirm the spec. A delivery dock-stamped “MGP10 KD H2” but reading 25% MC on the meter is a reject. Drying timber on site is not a remediation; bounce it back.
- Before fixing internal linings: framing above 18% MC will keep shrinking after plasterboard goes on, causing pops and joint cracks. Wait or ventilate the structure.
- Before painting or staining: confirm substrate MC is at finish-tolerance (typically ≤16% for paint, ≤14% for oil-based stains).
Meter accuracy. Pin meters read at depth of pin insertion (typically 8 to 15 mm). Pinless meters read a surface zone (10 to 25 mm depth) and are less accurate at deep cores. Both are species-corrected; check the meter’s calibration for the species being measured.
Limitations.
- Surface moisture from recent rain reads high even if the core is dry. Wait or test below surface depth.
- Frozen moisture in cold conditions reads inaccurately on pinless meters.
- Treated timber carries chemical actives that can affect both meter types; consult the manufacturer for correction factors.
Also known as: MC, wood moisture, EMC (when at equilibrium).
Category: Materials / timber / moisture.
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Last updated: 2026-05-14. Verified: 2026-05-14.