How do you recognise quality wood when buying?
The Wood Guide · Calculating with wood
Buying guideRecognising quality wood
Buying good wood starts with looking carefully. Five checks you do yourself, at the stack, before you pay.
- Moisture · grain · knots · colour · straightness
- 8–10% for indoor furniture
- Sight along the board
Good timber for what?
A board full of knots is worthless for a window frame and exactly right for a farmhouse table. The question is never "is this good timber", but "is this good timber for what I am going to do with it".
Click a chapter or use the arrows · schematic drawings.
Quality depends on the use
There is no absolute standard for "good wood". What is perfect for a rustic table is unsuitable for fine cabinetmaking.
A board full of knots is worthless for a window frame and just right for a farmhouse table. A moisture content of eighteen per cent is fine for a garden structure and far too high for indoor furniture. So the question is never "is this good wood" but "is this good wood for what I am going to do with it".
With that question in mind, there are five things you can check on the spot, with no tools except perhaps a moisture meter.
Sight along the board: hold it at eye level and look along its length, as a carpenter does. In two seconds you see bow, twist and cupping — more than with any other check. Do this with every board you take from the stack.
- Moisture content indoors
- 8 to 10% for furniture wood
- Moisture content outdoors
- 15 to 18% is normal
- Grain
- regular and tight = stronger
- Knots
- sound and small for construction, loose = falls out
- Discolouration
- blue stain is cosmetic, soft wood is not
- Straightness
- sight along the board, always
To be fair: the best board from a bad batch is still a bad board. If the whole stack has been stored too wet, has lain outside under a leaking tarpaulin or is obviously freshly sawn, picking through it will not help. Walk on — there is always another supplier.
Five things you can see yourself
- 1 · Moisture contentThe moisture content determines whether the wood will still shrink, crack or warp after you have worked it. For indoor furniture wood you want 8 to 10 per cent, for garden timber 15 to 18. Measure with a moisture meter, or feel: cool and clammy at the end grain means too wet.
- 2 · Grain and structureThe grain determines both strength and appearance. Straight, tight grain makes maple ideal for chopping boards; wide, irregular growth rings point to fast growth and therefore lower weight and less strength. Look at the regularity on the end grain.
- 3 · KnotsAround a knot the grain direction changes, and the wood is weaker there. For mouldings and window frames you look for knot-free; for a farmhouse table they are part of it. Check whether a knot is sound — a loose one will fall out sooner or later.
- 4 · DiscolourationGrey-blue streaks are usually blue stain: cosmetic, no loss of strength. But dark, soft spots that give under your thumb are rot, and that board belongs in the stove.
- 5 · StraightnessSight along the length of the board. You see straight away whether it is bowed (curved along its length), twisted (turned around its axis) or cupped (hollow or domed across its width). Twist is the hardest to get straight — leave those boards.
Which quality for which job
| Project | Moisture content | Knots | Main requirement |
|---|---|---|---|
| Indoor furniture | 8 to 10% | To taste | Dimensional stability and straightness |
| Window frame or door | 10 to 12% | Knot-free | Dimensional stability above all |
| Structural timber | about 18% | Sound and limited | Strength class (C24) on the stamp |
| Garden timber | 15 to 18% | Sound | Durability class and treatment |
| Decking boards | Kiln-dried | Sound | Straight and not twisted |
| Chopping board | 8 to 10% | None | Tight, straight grain |
Graded structural timber carries a stamp with the strength class (C18, C24, C30), the moisture class and often the producer. If it is missing, it is ungraded timber that you must not rely on in a load-bearing structure. See structural timber.
What you do at home
Let it acclimatise
Leave the wood for one to two weeks in the room where it will stand, before you work it. That way it reaches its equilibrium moisture content before assembly instead of after.
Store flat and supported
On sticks every fifty centimetres, so air can get all around it. A stack lying flat on the ground draws moisture from below and warps from above.
Not in the sun or next to the heating
Fast, one-sided drying is exactly what causes cracks.
Seal the end grain
For thick wood that still has to dry: a coat of paint or wax on the end grain slows down the drying there, and that prevents cracks.
Frequently asked questions about assessing wood when buying
What moisture content should wood have?
For indoor furniture wood 8 to 10 per cent, for window frames 10 to 12, for structural and garden timber about 15 to 18. Wood that is too wet shrinks and cracks after it has been worked.
Are knots bad?
Not necessarily. The wood is weaker around a knot, though, so for construction and window frames you want few of them. For a farmhouse table they are part of the look. Always check that they are sound.
What do blue streaks in wood mean?
Usually blue stain, caused by storage that was too damp. It is cosmetic and does not affect strength. Dark, soft spots that give under your thumb, on the other hand, are rot.
How can I tell whether a board is straight?
Sight along it: hold it at eye level and look along its length. In two seconds you see bow, twist and cupping. A twisted board never becomes completely straight again.
Buying in perspective
Five checks, two minutes, and you know more than most buyers.
Have a question about your project? Just ask — we're happy to help.
Photos via Wikimedia Commons: Insjön, Sweden — Edaen, CC BY 3.0 · Piece of softwood with two knots, the grain bending around them — 01x07x2022000, CC0 · Picea abies — Moinats, CC BY-SA 4.0