Buying timber: what to look for and what to reject

Learn to check timber for straightness, moisture, knots and size before you buy it.

BT-01Know what you're buyingSoftwood (pine, spruce) is cheaper and easier to cut; hardwood (oak, ash) is stronger and pricier. 'Sawn' timber has a rough surface and full size (a 100mm sawn batten is genuinely about 100mm). 'PSE' (planed square edge) is smooth but a bit smaller than its name suggests, because planing shaves off a few mm. Treated timber (usually greenish or brown-tinted) resists rot outdoors; untreated is for indoor use only.

BT-02Sight down the lengthHold one end of the plank at eye level and look down its length like you're aiming a rifle. You're checking for bow (a curve along the flat face), cup (a curve across the width, like a shallow trough) and twist (each end sits at a different angle, so the plank looks like a propeller). A little bow is normal and can be worked with; a twisted piece will never sit flat and should go back on the rack.

BT-03Check it isn't wetWet timber is heavier than it looks, feels cold and damp to the touch, and sometimes smells musty. It shrinks and can twist badly as it dries out after you've built with it. If two identical-looking planks feel very different in weight, pick the lighter one - the heavy one is holding water.

BT-04Inspect knots and edgesKnots are the darker circular marks where a branch grew from the trunk. A tight, dark knot is fine and just cosmetic. A knot that's ringed with a dark gap, or that you can push and it moves, is a 'dead knot' - it can fall out and leave a hole. Also check the edges for wane (where the rounded outer bark edge of the tree is still there, cutting into the corner) and for splits running along the grain at the ends - both weaken the piece.

BT-05Check the actual sizeTimber is sold by a 'nominal' size, like 47x100mm, but the real size is often a few mm smaller once it's been planed. This matters if you're matching it to something else, like a stud wall or a shelf bracket. Measure a few pieces with a tape measure before you commit, especially if the exact fit matters.

BT-06Know what to rejectPut back anything with a visible twist, a large dead knot near the middle of a span, deep splits at the ends, obvious wet patches, or heavy wane along an edge you need to be straight. The beginner mistake is grabbing the first plank on the pile - always dig a few pieces back, since the top of the stack is often the ones everyone else already rejected.

BT-07Confirm you chose wellBack home, lay the timber on a flat surface like a table or the floor. It should sit without rocking or gapping badly at the corners - a small gap is fine, a big one means it's still bowed or twisted. Give it a squeeze at the ends: no give, no soft or spongy feel, and no lingering damp smell. If it passes all that, you've picked well.

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