Test salvaged wood by pushing an awl into it, because sound wood resists and rotted wood is soft; look for insect holes and tunnels, sight along each board for twist, cup and bow, and cut off checked ends, allowing 5-10 cm of waste at each end. Use only sound, straight, solid wood where it carries load, and put doubtful pieces into non-structural work, because rot and tunnelling inside a board cannot always be seen from outside.
Part of Building Material Recovery
Wood fails from water, insects and drying stress, and a board that looks fine can be hollow or soft. Assessment sorts wood into load-bearing, non-structural and firewood.
Rot And Tunnelling Decide Whether A Board May Carry Load
Rot test. Push an awl, nail or knife tip into the wood. Sound wood resists penetration; rotted wood is soft and the tool sinks in easily. Check the end grain especially, because rot starts where water enters (parent article).
Insect damage. The parent article gives the signs: small round holes of 1-2 mm are powder post beetles; larger oval holes of 10-12 mm are carpenter bees; galleries or tunnels visible in cross-section are termites or carpenter ants. Surface damage is cosmetic; extensive internal galleries compromise structural integrity.
Warping. Sight down the length of the board. Twisting, cupping (curling across the width) and bowing (curving along the length) are common in boards that dried unevenly. Mild bowing can be corrected by fastening to straight framing. Significant twisting makes a board unusable for flat applications but fine for rough framing or firewood.
Checking (end cracks). Cracks along the grain at the board ends. Cut past the checks to sound wood, and allow 5-10 cm waste per end when estimating usable length (parent article).
What You Need
- An awl, a nail or a knife.
- A straightedge or string, for sighting.
- A tape and saw.
- Good light. Daylight shows rot and holes best.
Method: Probe, Look, Sight, Trim
Step 1: Probe the ends and any wet-looking section with the awl. Soft spots, crumbling or a musty smell mean rot.
Step 2: Look for holes and tunnels, including at cut ends.
Step 3: Sight each board from one end, then the other. Mark twisted or cupped boards.
Step 4: Trim the checks. Cut past the cracks to sound wood.
Step 5: Classify. Sound and straight: structural. Slightly warped or lightly damaged: non-structural framing, shelving or sheathing. Rotted or tunnelled: firewood or kindling, after checking for treatment and paint cautions.
Step 6: Proof-test before relying on it. For a beam or joist that will carry load, support it at the ends and load it gradually with weights while watching it, with people clear of the underside. A board that cracks, creaks or sags badly is not for load-bearing use. Choose the test load by the job, with a generous margin.
Worked Example
A 2.4 m board has checks at both ends. Allowing 5-10 cm of waste per end, the loss is 2 × 5 = 10 cm to 2 × 10 = 20 cm. The usable length is 240 − 10 = 230 cm down to 240 − 20 = 220 cm, so plan for 2.2 to 2.3 m, not 2.4 m.
Common Mistakes
- Judging by the surface. Hollow rot may sit under a sound-looking skin.
- Using a warped board as a straight beam. It bends further under load.
- Cutting to the full length including the checks. The cracks run into the cut piece.
- Reusing wood with active insects in a new building. They can infest other timber; burn or discard it where that is safe.
Safety
A bad board in a load path fails without warning
Rotted or tunnelled wood can break suddenly under load, and a collapse of a floor, roof or scaffold built from it can injure or kill. Use only sound wood in load-bearing roles, proof-test beams with people clear, and wear a respirator and gloves when working mouldy wood. Do not burn treated or painted wood; see Asbestos, Lead Paint & Other Hazards.
What’s Next
- Learn next: Dimensional Lumber vs. Engineered Wood — which products can be reused
- Combine with: Denailing & Board Cleaning — the step before you assess